US3136158A

US3136158A - Variable speed tensile tester

Info

Publication number: US3136158A
Application number: US48716A
Authority: US
Inventors: Jr Prentice C Wharff; Jr Kenneth R Oliver
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-08-10
Filing date: 1960-08-10
Publication date: 1964-06-09
Anticipated expiration: 1981-06-09

Description

June 9, 1964 P. c. WHARFF, JR.. ETAL 3,136,158

VARIABLE SPEED TENSILE TESTER 5 Sheets-Sheet 1 Filed Aug. 10, 1960 June 9, 1964 P. c. WHARFF, JR., ETAL 3,136,158

VARIABLE SPEED TENSILE TESTER Filed Aug. 10, 1960 5 Sheets-Sheet 2 N \h \N a m xXk u qqgQU I Us 5 ATTORNEY June 9, 1964 P. c. WHARFF, JR., ETAL 3,136,158

VARIABLE SPEED TENSILE TESTER 5 Sheets-Sheet 3 Filed Aug. 10. 1960 INVENTOR5 MM%W/ ATTORNEY June 9, 1964 P. c. WHARFF, JR., ETAL 3,

VARIABLE SPEED TENSILE TESTER Filed Aug. 10, 1960 5 Sheets-Sheet 4 ATTORNEY June 9, 1964 P. c. WHARFF, JR., ETAL VARIABLE SPEED TENSILE TESTER 5 Sheets-Sheet 5 Filed Aug. 10. 1960 llllllllll 8 1 INVENTOR5 MMCE C.

. ATTORNEY United States Patent 3,136,158 VARIABLE SPEED TENSILE TESTER Prentice C. Wharff, Jr., 3212 Los Palos Circle, Lafayette, Calif., and Kenneth R. Oliver, Jr., 26 Woodhaven Road, Newport News, Va.

Filed Aug. 10, 1960, Ser. No. 48,716 16 Claims. (Cl. 7389) This invention relates to tensile testers and is particularly directed to an improved apparatus for more accurately determining tensile properties of specimens, such as single fibers, filaments, and similar unitary elements, and to provide for manual and automatic control of the equip ment with a direct indication of the stress-strain characteristics of samples undergoing tests.

The measurement of stress-strain characteristics under various control environmental conditions and at various rates of extension provide important information in fiber research work. It is important for the performance of some tests that at least that portion of the apparatus which stresses the fibers be of small size and be remotely controllable, so that it may be operated in an environmental cabinet for certain types of tests. It is also desirable that manual as well as automatic control be available for repetitively stressing and relieving specimens undergoing tests. In addition, it is desirable that the apparatus be built in three cooperating and connected but physically separated portions or units, which can be spaced from each other to provide more versatility in the conduct and control of tests. These units prefer-ably comprise a filament puller or stresser, a remote control box, and a recorder incorporating certain control circuits.

The filament puller or stresser basically incorporates the force and elongation transducers and drive systems. This portion of the apparatus is the part which preferably is made relatively small, so .that it can be readily placed in an environmental cabinet, if desired. The drive mechanism for the filament puller may contribute very appreciably to its adaptability for the performance of a variety of tests and comprises gearing which can be readily replaced for different ratios of gear reduction to obtain a variety of rates of extension. In addition, a motor mounting is provided which facilitates replacement of the filament puller drive motor, so that motors for direct drive or gear motors may be easily interchangeably mounted for driving the filament puller gearing at variouspredetermined rates. It also incorporates features 'in the electri cal and mechanical drive system for stressing test samples which provide a maximum degree of flexibility with respect to test sample lengths and modes of operation. Among these is an arrangement for the rapid return of the extension yoke, which is independent of the extension drive rate and independent of the normal motor return drive. In addition, this part of the apparatus incorporates a reversible drive which provides for the performance of hysteresis tests, as well as stress-strain tests for determining the modulus of elasticity, elastic limit, yield point, and maximum or ultimate strength characteristics of test samples.

The remote control box preferably includes the various circuit making, breaking, andchanging devices for man ually and automatically controlling the operation of the filament puller, which devices are not primarily governed by characteristics of the sample undergoing tests. This facilitates the performance of the various tests under controlled ambient conditions and provides for emergency control of the operation of the filament puller. In addition, the remote control box is provided with position or condition indicating signal devices which inform an operator of the position or condition of certain parts of the filament puller mechanism. It preferably also is provided with a suitable control, such as apotentiometer, for varying the response of the recorder with the cross section of -a test sample, so as to indicate stress per unit cross sectional area. These all cooperate to adapt the apparatus to the performance of a wide variety of tensile tests.

The recorder portion of the apparatus may comprise any suitable two-coordinate recorder capable of plotting a curve along the coordinates representative of the stress strain characteristics of the test specimen. This recorder preferably is provided with certain automatic circuit controlling members, which are primarily responsive to characteristics of the test specimen as determined by the filament puller and transmitted to the recorder as suitable electrical signals. Some of these circuit controlling members may be rendered non-responsive for the performance of certain types of tests, and, in a simplified form of the present apparatus, certain of these circuit controlling members may be entirely omitted. These characteristicresponsive circuit controlling members in the recorder may take the form of a series of microswitches operable in response to the desired control conditions for closing or opening circuits which govern the operation of certain aspects of the filament puller mechanism.

Among such control members may be one arranged to assure a true indication of strain or elongation of a test sample. This member may conveniently comprise a suitable microswitch operable by the recorder after the test sample has been placed under a predetermined stress, such as 2 percent of the maximum stress which can be indicated or recorded by the recorder. This assures against a false indication of strain or elongation of a test sample while the filament puller is merely being driven to the point Where stress is about to be applied to the specimen, as might readily occur if the initial specimen were curled or kinked such that it would be necessary to straighten the test filament prior to the actual application of stress thereto.

Another control member in the recorder may comprise a microswitch which is responsive to stress reversal as indicated by the operation of the recorder, as when a filament breaks. This member preferably controls a circuit for stopping the operation of the filament puller drive mechanism and for automatically operating the extension yoke rapid return mechanism. Under certain conditions, as for the performance of hysteresis tests, this latter stress reversal responsive control must be rendered inoperative, so that the test sample may be repetitively stressed and relieved of stress, under controlled rates of operation of the filament puller in opposite directions. .For such tests, the extension yoke rapid return device must remain in inoperative condition. Furthermore, for determining hysteresis characteristics of a test sample, it might be desirable automatically to decrease the stress on a sample beyond a predetermined strain and automatically to restress the sample when the strain has been reduced to zero. It also may be desirable to vary the predetermined strain at which the decrease in stress automatically begins, so that a variety of hysteresis characteristics may be obtained. These features may be obtained by providing suitable microswitches on the recorder whichcontrol the direction of rotation of the extension yoke drive motor and provide for the response of these microswitches to predetermined strain values as indicated by the recorder.

It also is desirable to provide for-rendering the filament puller inoperative beyond a predetermined strain equivalent to the full scale deflection of the recorder. This will prevent damage to the recorder and includes an arrange ment for controlling the filament puller so as to return it to its initial or zero stress-strain position for the commencement of another test.

An object of this invention is to provide an improved tensile tester.

Another object of this invention is to provide a tensile tester specifically improved to perform tensile tests on single filament specimens, either under automatic or manual control.

A further object of this invention is to provide an improved tensile tester with features which are automatically operable in response to the occurrence of certain predetermined conditions.

Still another object of the'present invention is to provide a versatile tensile tester which will give a direct indication of the stress-strain relationship of a specimen undergoing a tensile test, with a correction of the relationship to indicate the force per unit cross sectional area of the test specimen.

A yet further object of the present invention is to provide a tensile tester which is particularly constructed for testing single filament specimens in controlled ambients.

Yet another object of this invention is to provide an improved tensile tester for performing hysteresis tests on relatively small filaments, either automatically or under manual control.

An additional object of this invention is to provide an improved filament tensile tester with safety features for rendering the test mechanism inoperative and returning it to its zero or initial starting position under certain conditions which might result in damage to the equipment.

Further objects and advantages of this invention will become apparent from the following description, referring to the accompanying drawings, and the features of novelty which characterize this invention will be pointed out with particularity in the claims appended to and forming a part of this specification.

In the drawings:

FIG. 1 is a perspective view of a tensile tester made in accordance with the present invention, partsof which are schematically illustrative of certain members of the apparatus, particularly of those within the recorder;

FIG. 2 schematically illustrates the tensile tester shown in FIG. 1, giving details of the electrical circuits of the apparatus;

FIG. 3 is a side elevational view of the tensile tester filament puller shown in FIG. 1, partially broken away and partially schematically illustrated, showing the operative relationship of parts of the driving mechanism of the filament puller taken along a broken section indicated by line 3-3 in FIG. 4;

FIG. 4 is a side elevational view taken along line 4-4 of FIG. 3, partly broken away and partly in section, illustrating further the detailed relationship of certain parts of the driving mechanism for the extension yoke of the filament puller;

' FIG. 5 is a sectional view of the lower bearing guide block for the extension yoke of the filament puller, taken along line 5-5 of FIG. 3;

FIG. 6 is a sectional side elevational view of the filament puller, taken along line 66 of FIG. 3, showing the arrangement of the external gear train for driving the elongation measuring potentiometer; and

FIG. 7 is a fragmentary plan view showing the mounting of the drive motor in the housing.

Tensile testers are useful in determining tensile characteristics of various types of materials which may be used for many purposes, varying from a rubber band or a fiber used in the production of fabric or clothing to metallic elements which may be used for many purposes from musical instruments to large structural beams and tie members. All such structural elements have certain fundamental characteristics which have become recognized in the trades as indicative of certain qualities of the elements and of the materials of which they are composed. The most important of the tensile properties are generally those which may be illustrated by a stress-strain curve and which may be determined by suit able tensile tests.

Until relatively recently the testing of single fiber or filament specimens was undertaken primarily as a matter of academic interest. This was due primarily to the fact that until recent years fibers used in the manufacture of fabrics generally were natural products obtainable from natural sources, such as wool, cotton, flax, etc., over the production of which little control could be exercised. With the advent of synthetic fibers, it has become important to the fiber manufacture to be able to determine and predict tensile properties, both for the improvement of the synthetic fibers and to enable the manufacturer to be able to specify the physical properties of fibers to assure the quality of materials which he sells or uses for the manufacture of textile products.

The properties of single fibers or filaments have, therefore, become the common ground between the fiber and textile manufacturers, and consequently reliable tests for determining the tensile properties of single fibers have become very important. Furthermore, the behavior of fibers in different ambients is of considerable importance, as tests under one set of ambient conditions may very well provide results which are very materially different from those obtainable in a .dilferent environment. It, therefore, becomes important to be able to test the physical properties of single fibers or filaments under a'variety of ambient conditions and directly to compare the results of such tests.

The illustration of test results by stress-strain curves not only facilitates a comparison of tensile properties of a particular type of fiber under different ambient conditions, but also facilitates the comparison of tests of different types of fibers under the same ambient conditions. Such stress-strain curves readily yield important information by a simple inspection of the curves. Among the important physical characteristics indicated by such curves is the well-known Youngs modulus, also known as the modulus of elasticity or elastic modulus, which is represented in a stress-strain curve by a substantially straight line portion wherein a unit stress per unit cross sectional area produces a definite deformation per unit length of the specimen. This elastic modulus also may be used to represent the stress below a certain value which will produce a definite deformation of a specimen, from which deformation the specimen will return to its original dimensions when the stress is removed without any resulting permanent deformation of the specimen.

This elastic characteristic of materials occurs at stresses below a value known as the elastic limit of the material which generally appears as a definite knee or bend in the stress-strain curve, just slightly below the yield point or yield strength. Stress beyond the elastic limit causes permanent deformation of the specimen, although it may not be sufiicient to cause breaking of it. As a rule, it is desirable to continue a tensile test until the specimen actually breaks, so that its maximum strength under stress can be determined. This maximum strength is known as the tensile or ultimate strength of the specimen being tested and is indicated by a final sharp break in the stressstrain curve. In some instances, the curve between the terminal points marked by the yield point and the ultimate strength point may be of considerable importance as the specimen may continue to elongate with substantially no additional load at a point slightly beyond the elastic limit of the specimen. This may prove to be very undesirable for certain uses as it might result in an excessive permanent elongation of material formed of the fibers which will make the material useless for its originally intended purpose.

In addition, it is desirable to be able to determine hysteresis characteristics of fibers, as for many purposes materials formed of fibers are subjected to repeated tension and it is highly desirable that the materials be restored to their original condition with substantially no permanent deformation. Certain fibers will be found to have different hysteresis characteristics under different ambient conditions, and it, therefore, is very important to be able to determine whether or not fibers will have relatively uniform and permanent hysteresis characteristics under different ambient conditions, or, if the characteristics vary, it is important to be able to predict the nature of such variations.

The design of any tensile tester must, therefore, be predicated upon a knowledge of the general range of quantities which the characteristics of materials to be tested may possess. The embodiment of the present invention which is illustrated in the drawings represents a tensile tester which is especially useful for determining tensile characteristics of fine fibers and filaments. The general structural arrangements and the control and indicating circuits can equally well be utilized for testing specimens of greater size and generally possessing characteristics wherein the stress and elongation may be many times those of small fibers and filaments. The present description and reference to the drawings generally will be limited to terminology applicable to the tensile tester shown, and such description is to be taken only as illustrative of an application of the present invention.

The illustrated embodiment of the present invention preferably is built in three cooperating and connected but physically separated portions or units, which can be spaced from one another to facilitate the control of various tests. In addition, the mechanical drive of the tensile tester is adapted to provide different predetermined rates of operation. These rates of operation should be definitely reproducible under widely varying conditions and at widely spaced intervals. This is obtained in the illustrated embodiment by providing a separate filament puller 1, wherein drive motors each having a fixed speed may be quickly and easily interchanged for providing different rates of operation of the tensile tester. In addition, the illustrated tensile tester is constructed so that readily interchangeable sets of gears can be mounted for transmitting the driving power from the motor to the fiber-stressing member at different gear ratios, so that for a given fixedspeed motor a variety of fixed rates of operation of the tensile tester also are obtainable.

The major control members and circuits of the tensile tester preferably are incorporated in a single casing or control box 2, as shown in FIGS. 1 and 2, which is separate from the filament puller and recorder. This provides for the remote control of the operation of the tensile tester and can be used with a simple two-coordinate recorder or with a recorder having one or more of the auto matic control features shown in FIGS. 1 and 2 which enable the performance of additional tensile tests responsive to various conditions which are indicated by the recorder. Both the remote control box 2 and the recorder 3 are adapted to be connected together and to the filament puller 1 by suitable plug type terminals to facilitate arrangement of the different parts of the apparatus for different tests and to provide for interchangeably using different types of recorders.

In order to test fine fibers and filaments and to provide for a ready comparison of test results, it is desirable that the dimensions, such as the cross sectional area and the length of the specimens, be substantially constant for all comparable tests, so that the mechanical and electrical systems can be designed to provide indications of elongation or strain of the fibers in terms of a unit area and a unit or a constant gage length.

For any given material having a definite density the measurement of the size of the fiber in terms of deniers provides a definite measurement of the cross sectional area of the specimen fiber, although the denier of fibers technically is a measurement of the weight of the fiber for any predetermined length. Artisans in the field of fibers, filaments, fabrics, and similar materials, generally refer to the denier of a material in order to indicate the size thereof, and, in view of this generally accepted terminology, the term denier is used interchangeably with the term cross sectional area in the present disclosure to designate the size of specimen fibers and filaments.

With modern techniques for securely holding the ends of test specimens, it has been found that accurately comparable test results are obtainable by fixing the gage length of specimens and measuring or recording elongation or strain of a specimen undergoing test after the specimen has been subjected to a predetermined stress. This makes is possible to record elongation or strain of a test sample directly by a recorder without the need of correcting for variations in gage length or reducing the strain to terms of elongation per unit length or to a percentage of gage length.

In the illustrated apparatus, a test, specimen fiber 4 is shown with the ends thereof adhesively secured to tabs 5 and 6, so that the length between the ends of the specimen secured to the tabs is readily maintained at a definite value. Details for thus securing filaments are described in copending application Serial No. 851,336, K. R. Oliver, Jr., entiled Test Specimen Filament Mounting, filed November 6, 1959, now Patent 3,063,294, November 13, 1962. This type of mounting for test specimens provides for quickly and easily mounting the specimen on the filament puller portion of the present tensile tester, but other suitable arrangements for holding the ends of test speci mens without deformation may be used.

Each of the tabs 5 and 6 preferably is formed with an aperture 7 therethrough, which can readily be slipped over an end 8 of a fastening hook 9 secured in any suitable manner, as by a pair of nuts 10, to a tension bar 11 of a suitable strain gage 12. The other end of the specimen 4 secured to the tab 6 is adapted to be engaged by a tab gripping and holding element 13 securely fastened in any suitable manner to an extension yoke base 14 against a shoulder 15 thereon. The holding element 13 preferably is formed with a pair of tab gripping claws 16 which are separated by a narrow slot 17, substantially along the longitudinal center line of the tab holding element 13. The tab 6 is merely slid under the downwardly extending claws 16 with the end of the test specimen 4 extending through the slot 17 out of engagement with the claws 16 to provide a uniform and quick means for holding the lower end of a specimen. The base 14 is mounted on a drawbar 18 and is secured thereto in any suitable manner, as by a pin or set screw 19. The entire member for holding the lower tab 6 is adapted to be operated by the filament puller by being readily removably secured to an extension yoke 20 by any suitable attaching means, such as conventional wedge block clamping jaws 21. With such an arrangement, a specimen fiber 4 can be quickly and easily mounted between the strain gage hook 9 and the extension yoke claws 16, while the extension yoke 20 is in a raised position with the distance between the end 8 of the hook 9 and the underside of the jaws 16 less than the distance between the securing portions of the tabs 5 and 6. Thus, when it is desired to stress the test specimen 4, the extension yoke 20 is operated to take up the slack in the test specimen by being moved downwardly and eventually to exert force on the lower end of the test specimen, which force is transmitted through the specimen to the tension bar 11 of the strain gage, which measures this force as the stress on the specimen.

Preferably the strain gage 12 is of the unbonded resistor type, which transmits an electrical signal of an intensity which varies in accordance with the magnitude of the tensile force transmitted to it by the tension bar 11. The internal circuitry of such a gage is essentially a Wheatstone bridge circuit connected between terminals 22, 23, 24, and 25. This strain gage may comprise any conventional gage of this type, which can be suitably mounted on the filament puller. Such strain gages operate in accordance with the well-known principle that the resistance of a conductor changes with its elongation,

so that a tension placed on certain terminals of the strain gage will unbalance the Wheatstone bridge.

In the illustrated system, energization of the strain gage bridgeis provided by a suitable electrical source, such as a battery 26, connected across the gage terminals 22 and 24 through a suitable potentiometer R The potentiometer R preferably is mounted in the remote control box 2, while the battery 26 may be mounted in any convenient location, such as in the filament puller 1 or the remote control box 2.

The circuitry of the strain gage is conventional for gages of the type mentioned and includes resistors R and R which are variably connected together, preferably as shown in FIG. v2, across three of the strain gage terminals to provide an adjustment of the electrical signals obtainable across terminals 23 and 25 of the strain gage. These gage terminals are adapted to be connected through suitable conductors 27 to a Y-axis control 2-8 in the recorder 3, FIG. 1, which provides for plotting, on suitable coordinate paper in the recorder, the stressapplied to the test specimen 4. With this type of strain gage circuitry, a potential difference is produced across the strain gage terminals 23 and 25 which is proportional to the tension on the strain gage transmitted through the tension bar 11 from the test specimen 4. This is the potential difference which provides the electrical signal transmitted by the conductors 27 to the recorder Y-axis drive control 28.

This strain gage and its associated circuit provides a means for readily transmitting the indication of stress on a specimen fiber to the recording instrument, such as the recorder 3 and acts as a very simple basic force transducer which can easily be adjusted. to compensate for variations in the cross sectional area of a test specimen. Generally, tensile test equipment indicates or records stress in terms of the actual force applied rather than in terms of force per unit cross sectional area. This is practical where the test specimen has a relatively large cross sectional area which can be held within reasonably close limits. Synthetic fibers, as conventionally produced, often have relatively wide variations in cross sectional area, even when produced by the same equipment. This variation may be as much as percent either way from the average for individual filaments. In view of the wide variation between production samples of single fibers, stress-strain curves in which the force or stress is plotted in terms of grams vs. elonga tion would have a 10 percent scatter on either side or the average due simply to variations in cross sectional area. This would make it extremely difficult to detect variations due to other factors. It is very important, therefore, that differences in cross sectional area be eliminated from the effects produced by the strain gage measurement of stress on a test specimen. This will result in normalizing of the stress-strain curves and provide an accurate expression of the stress on a test specimen in terms of force per unit cross sectional area, such as grams per denier. This is the corrective feature which is incorporated in the circuitry of the present'invention, including'the potentiometer R illustrated in FIGS. 1 and 2.

Preferably the potentiometer R is calibrated directly in deniers, which may be indicated on its control dial 29 mounted for easy visual observation on the remote control box 2, FIG. 1. In this manner, the denier of a test specimen can be determined beforehand, by a .vibro:

scope or otherwise, and, the control dial 29 of the denier potentiometer R may be set to indicate directly the denier of the test specimen, thereby providing a means for directly varying the response of the tension measure ment to stress on a test specimen in accordance with the cross section of the specimen. The shunting resistor R and the variable potentiometer connection of the resistor R to the resistor R provides a voltage divider circuit between the strain gage terminals 22, 23, and 24, by

which the electrical zero of the strain gage may be ad justed to calibrate the gage to provide a proper response thereof to stress placed thereon.

In order to provide tensile tests which will yield practical information regarding stress-strain characteristics of test specimens, it is desirable that the tensile force applied to a specimen be applicable in a uniformly repeti tive manner, both to a single; specimen for hysteresis characteristics and for corresponding tests of different specimens. This requires that specimens undergoing tests be held in a uniform manner and that the force be substantially uniformly and gradually varied. The tabs 5 and 6, to which the ends of the fiber specimen 4 are secured, together with the strain gage hook 9 and the tab holding element 13 provide a means for uniformly holdin" the two ends of a specimen for hysteresis test purposes and for tests of different specimens having predetermined gage lengths. Uniform application and variation of tension on a test specimen may conveniently be provided by a drive mechanism for the extension yoke 2i) which moves the two specimen holding members relative to each other at a predeterminable rate during the stressing of a specimen. Details of the extension yoke driving mechanism for thus stressing a specimen are illustrated in FIGS. 3 and'4.

As shownin these figures, a filament puller drive motor M is provided with a mounting flange 30, which can be easily slid into mounting slots 31 formed in a supporting frame structure 32 supported in the housing 33 of the filament puller 1. In order to assure a predeterminable fixed speed of operation of the extension yoke 20, the drive motor M preferably is a synchronous motor, and, in most instances, comprises a gear train mounted within the motor housing and driven by the motor, so that the drive shaft 34 of the motor M will operate at a predetermined relatively low speed. Power for the motor M is supplied through suitable conductors 35 connected in the control system by an easily connectable plug type terminal member 36. Thus, if it is desired to operate the filament puller at a diiferent predetermined speed, it is only necessary to unplug the motor terminal 36, remove the motor M from the filament puller housing 33 by lifting it upwardly through the uncovered portion 37, and replaceit with another drive motor M having the required speed of its output shaft 34 to provide the desired operating speed of the extension yoke 20. I

A suitable gear train is provided for connecting the motor drive shaft 34 to the extension yoke 20, and includes a pinion gear 38 drivingly mounted on the motor output shaft 34. This gear 38 is adapted to have a driving engagement with a spur gear 39 secured in any suitable manner, as by a set screw 40, to a countershaft 41.

In order to assure proper driving engagement between the motor pinion drive gear 38 and the countershaft gear 39, an adjusting screw 42 threadedly engages a boss 43, secured to the filament puller housing 33, and supports the motor flange 36 in the slot 31. As can more readily be seen by reference toFIG. 3, the adjusting screw 42 may be moved upwardly or downwardly relative to the boss 43 and thereby adjust the position of the motor mounting flange 3i) upwardly and downwardly respectively in the slot 31 with a corresponding adjustment of the pinion gear 38 relative to'the countershaft gear 39. This assures a proper alignment and proper driving engagement between the gears 38 and 39.

Power is transmitted from the countershaft 41 through a worm gear 44 which is drivin'gly secured to the countershaft 41 in any suitable manner, as by a locking key 45. The worm gear 44 has a driving engagement with the teeth of a worm wheel 46 drivingly mounted on a second countershaft 47 by any suitable means as by a set screw 48. This countershaft 47 is rotatably mounted in suitable bearings 49 in a mounting bracket hub 5'9, which is rigidly secured in any suitable manner, as by screws 51, to the filament puller housing 33. This same mounting bracket is provided with a pair of arms 52 which extend upwardly and inwardly from the hub 50 and are formed with suitable bearing openings therein for rotatably supporting the countershaft 41, as is more clearly shown in FIG. 3. A readily interchangeable part of the extension yoke driving gear train is mounted on the exterior of the filament puller housing 33 in order to provide for conveniently changing this part of the gear train for obtaining various rates of operation of the extension yoke 20 with any given fixed-speed drive motor.

Such gear trains can be very easily computed to give different extension rates with fixed centers for the shafts on which the different gears of the gear trains are mounted. These gears preferably all are in the form of spur gears and the mechanics of computing the number of gear teeth and matching diameters need not be considered, as these involve only conventional computations which readily can be made to give the desired results.

This exteriorly mounted gear train includes a spur gear53 drivingly mounted on the countershaft 47 and arranged in driving engagement with a driven gear 54. This gear 54 is rotatably mounted on a stub shaft 55 supported on the housing 33, and is of such size as to provide a predetermined speed reduction between the gear 53 and the gear 54. The gear 54 preferably is formed with a hub 56 integral therewith and with a smaller spur gear 57. Spur gear 57 drivingly engages another spur gear 58 which is drivingly mounted on driven shaft 59. This provides the final desired speed relation between the motor output shaft 34 and the input to a main clutch CL The shaft 59 preferably is rotatably supported by a suitable bearing in an end shield 68 of the clutch CL and interiorly thereof, with suitable connections for transmitting power from the driving motor M to the driven parts of the operating mechanism of the filament puller through this clutch. Preferably the clutch CL is of the electro-mechanical type, which provides for a positive drive and yet allows for substantially instantaneous de coupling under certain driving conditions similar to overrunning or free-wheeling if the normally driven member of the clutch operates at a higher speed than the member which normally is the driving member thereof.

The electrical part of the clutch allows this free-wheeling to take place while the mechanical part of the clutch provides for the positive drive in either direction when power is being transmitted through the clutch from the motor M Any suitable conventional electro-mechanical clutch, such as an electromagnetic clutch with a crown tooth mechanical drive, can be used to provide this main drive clutch connection of the driving system. The electromag netic parts of the clutch may include a suitable energizing winding, preferably mounted in the drive member 61 of the clutch, and the driven part of the electromagnetic portion of the clutch is mechanically connected to the crown tooth driving member of the mechanical portion of the clutch. The driven member 62 of the crown tooth portion of the clutch is mechanically connected to a main drive shaft 63 of the filament puller, and is rotatably mounted in bearings within the main clutch GL and in a suitable bearing 64 mounted in the filament puller housing 33.

When power is transmitted from the drive motor M to the extension yoke 20 through the main clutch CL and the main drive shaft 63, this power is transmitted through a spur gear 65 drivingly mounted on the shaft 63 and arranged in driving engagement With a gear rack 66, which may be formed integrally with the extension yoke 20 or may be a separate member which is fixedly and drivingly mounted on the extension yoke 20. The yoke is longitudinally slidably mounted in a bearing 67 supported in a collar 68 secured to a cover 69 of the filament puller housing 33, and the other end of the yoke 20 is longitudinally slidably supported in a special guide bearing 70, FIG. 3. This guide bearing 70 has a partially cylindrical opening 71 therein to receive the cylindrical portion of the extension yoke 20 and a substantially rectangular slot 72 broached or otherwise suitably formed in one side of the bearing in communication with the cylindrical opening 71. The cylindrical opening 71 of the bearing 70 supports and guides the extension yoke, and the rectangular slot 72 provides for the free passage therethrough of the gear rack 66 as it is driven by the spur gear 65.

The upper end of the extension yoke 20 is provided with a quick-return mechanism and includes a small threaded shoulder 73 of slightly less diameter than the major portion of the extension yoke on which the gear rack 66 is mounted, and a piston 74 mounted on this shoulder and secured in position in position in any suitable' manner, as by a nut 75. The piston 74 preferably is provided with a suitable sealing ring 76, such as a conventional O-ring, and this assembly is slidably mounted within an air cylinder 77. The cylinder 77 and the piston assembly on the extension yoke provide a means for quickly raising the extension yoke and returning it to its uppermost or zero position under certain operating conditions. This quick return of the extension yoke is obtained by supplying air to the cylinder on the lower side of the piston 74 adjacent to the driving portion of the extension yoke and is controlled by a suitable double-acting valve A Preferably, the quicloreturn mechanism is rigidly mounted on the filament puller housing 33 through a mounting flange '78 at the lower end of the cylinder 77 arranged in engagement with the upper surface of the collar 68. This mounting flange also locks a sealing 0r stufiing box bushing 79 between the flange 78 and the sides of a recess in the upper side of the collar 68. This assembly is secured together in any suitable manner, as by studs 80 which extend through the mounting flange 78, the collar 68, and the housing cover 69. This forms a sealed air chamber within the cylinder 77 between the piston sealing ring 76 and the sealing bushing 79.

Air pressure is adapted to be supplied into the cylinder 77 from any suitable source for retraction drive of the extension yoke by the piston 74 and to be vented from the cylinder 77 when the extension yoke is driven downwardly by the drive motor M through a suitable tube 81, which communicates with the interior of the cylinder 77 through a passageway 81 in the mounting flange 78 and is sealingly secured thereto by a clamping nut 82. The double-acting valve A for control of the supply of air pressure to the cylinder 77 and the venting of this cylinder may conveniently be a solenoid type valve. Any suitable valve of this type may be used and is schematically illustrated in FIG. 2 as comprising a valve body 83 within a valve housing 84 connected to the cylinder air pressure supply tube 81 and constructed so as to provide communication between the cylinder 77 through the air supply tube 81 alternately with an air pressure supply 85 and a vent 86 to the atmosphere.

In this manner, when it is desired to operate the extension yoke 20 for a quick-return retraction thereof, air pressure is admitted into the cylinder 77 through the solenoid valve A from the air supply source 85 by raising the solenoid valve body 83. This actuates the piston 74-to its uppermost position in the cylinder 77 and draws the extension yoke upwardly at a relatively rapid rate, thus causing an overriding of the crown tooth mechanical portion of the extension yoke clutch GL The upper end 87 of the cylinder 77 is formed with a vent passage 88 to allow the exhaust of air from the cylinder 77 above the piston 74 during the retraction or upward stroke of the piston as it is actuated by air pressure on the lower side thereof. In order to cushion the piston 74 as it reaches the end of its upward stroke in the cylinder 77, the upper end of the extension yoke 20 is formed as a small plunger 89 of a diameter smaller than the threaded shoulder 73 and slightly smaller than the vent passage 88, so that as the piston 74 approaches the upper end of its stroke, the plunger 89 enters the vent passage 88 thereby restricting the escape'of air out of the cylinder 77 above the piston 74-. This causes a slight compression of the air entrapped in the cylinder 77 above the piston 74 and has a dashpot cushioning effect on the final portion of the return travel of the piston and therefore slowly retards the quick return of the exten sion yoke as it approaches its uppermost or zero position.

In a tensile tester for the measurement of stress-strain characteristics, it is desirable to obtain an indication of both the stress placed on the test specimen and the resultant strain thereof. In order properly to evaluate these two factors, a record of the simultaneous values thereof should be made so that their correlation can be readily determined. It is important, therefore, that both the stress on the specimen and the resultant strain or elongation thereof be measured.

In the illustrated embodiment of the present invention, stress is placed on a specimen filament d by moving apart the two tabs 5 and 6 which are secured to the ends of the filament. The stress on the filament is measured by the strain gage 12, which transmits an electrical signal proportional to this stress over conductors 27 to the recorder 3. The strain of the specimen filament 4 resulting from such stress can be measured in terms of the movement of the extension yoke 2% which places the stress on the filament. This movement of the extension yoke cannot be measured directly as a displacement of the yoke from its initial or zero position, as in this ini-' tial position a test specimen 4 would not be stressed, and it is only after the extension yoke has been driven downwardly some distance that the extension yoke exerts a tension on the specimen filament 4. It is therefore necessary to determine the position of the extension yoke at which a measurement of the strain or elongation of a specimen is to begin. This is facilitated if the length of specimens to be tested is standardized; that is, if the length between the points of attachment of a filament to the holding means, such as the tabs 5 and 6, is substantially fixed, so that the results of any set of tests for a given gage length can be readily compared. In this way it is possible to measure the strain or elongation of a test specimen 4 in relation to its original unstressed gage length. This can be done by measuring the movement of the extension yoke 20 after it begins to exert a stress on the specimen filament 4 or after it has exerted a predetermined percentage of stress on the test specimen.

In order thus to measure the elongation of a test specimen, the extension yoke 20 is connected to a measuring device through a clutch which provides for corresponding movement of the driving member of the clutch, while the driven member of this clutch is adapted to transmit power to a driven shaft only after the extension yoke places stress on the test specimen. Measurement of the movement of the driven member of the clutch, therefore, will provide a direct measurement of the elongation or strain on the test specimen filament 4 after it has been stressed.

This strain measuring device drive mechanism includes a spur gear 90 drivingly mounted on the main drive shaft 63 which drives the gear rack of the extension yoke 20 through the gear 65. Motion of the spur gear 90 is transmitted to a clutch drive gear 91 through an idler gear 92 mounted on a stub shaft 93. The clutch drive gear 91 is drivingly mounted on a clutch drive shaft 94 of a suitable type ofclutch CL which preferably is of the electromagnetic type, as this provides for a simple control which can be readily correlated with the remainder of the tensile tester.

Such an electromagnetic clutch comprises a driven member 95 mechanically connected to the main drive shaft 63 through the gear train including the gears 90,

' provided for energizing the electromagnetic clutch GL for transmitting power from the driven member to an elongation measuring device through a cooperating electromagnetic clutch member 96 and a clutch driven shaft 97. The elongation measuring device may conveniently comprise a potentiometer and, in the illustrated embodiment, includes a three-turn potentiometer 98 which is energized by any suitable source of electrical power, such as a battery 99. The elongation measuring potentiometer 98 is adapted to be driven from the clutch driven shaft 97 through suitable gearing, which is pref erably mounted on the exterior of the filament puller housing 33, so as to provide for easy replacement and interchangeability. In this manner, gear trains having different gear ratios may be quickly and easily substituted for driving the potentiometer from the clutch driven shaft 97 in accordance with the expected or possible strain of specimens being tested. Thus, if relatively little elongation or strain may be expected of a test specimen, the elongation between zero stress and the ultimate strength of the specimen can be magnified for bet ter analysis by a proper choice of gearing between the driven shaft 97 of the clutch CL and the elongation measuring potentiometer 98. This gearing normally will include a spur gear 100 drivingly mounted on the driven shaft 97 of the clutch GL and an idler gear 101, rotatably mounted on a stub shaft 102 secured to the filament puller housing 33 in any suitable manner, as by a screw 103, for transmitting motion from the spur gear 160 to a potentiometer drive gear 104, which is drivingly mounted on a potentiometer shaft 1%. The potentiometer shaft 1% is rotatably supported in any suitable manner, as by bearings 106 and 197 mounted in the filament puller housing 33.

In this manner, whenever the exciting winding of the elongation potentiometer clutch GL is energized as a result of stress being placed on 'a test specimen, further movement of the extension yoke 20 will result in a proportional movement of the elongation potentiometer so as to provide an electrical signal to conductors 198 and 109 for transmittal to the recorder 3 for providing an indication of the strain on the test specimen 4. This may be conveniently obtained by mounting a potentiometercontactor 110 on the elongation potentiometer shaft 105, so that the potential across the conductors 168 and 169 is directly proportional to the position of the potentiometer contactor 110 and therefore is directly proportional to the strain on the test specimen filament 4.

In the illustrated embodiment, the conductors 108 and 109 are conveniently connected to an X-axis drive control 111, which directly controls the operation of a servo-motor 112 mechanically connected through a suitable drive mechanism to a recorder pen 113. This pen drive mechanism may conveniently comprise a motor drive shaft 114 adapted to drive a drum 115 which transmits a proportional motion to the recorder pen 113 through a suitable driving cable 116, which extends around the drum 115 and a pair of idler pulleys 117 and 118. The driving cable 116 may be secured to the recorder pen 113 in any suitable manner, as by being attached by a set screw to finger 119 on the pen.

A correlated control and energizing electrical system is provided which facilitates arranging the three major components comprising the tensile tester for performing a variety of tests and for indicating or recording the test results on different indicating or recording instruments, as may be required by the nature of the tests being performed. To this end a single source of alternating current power supply preferably is connected to the electrical system of the tensile tester through a single plug type terminal 12-9, which can readily be inserted into any suitable outlet for connection to power supply lines L and L In this manner the power supply is trans- 13 mitted through a suitable flexible conductor 121 to the remote control box 2, and a main switch S is adapted to open and close the circuit of the tensile tester to the source of supply through the conductor 121.

The control circuits from the remote control box 2 which govern the energization of the filament puller opcrating devices are readily connectable to the filament puller system through a flexible cable 122 and a plug type terminal 123 containing the proper number of conductors and connectors for completing the desired circuits. Signals from the filament puller 1 are adapted to be transmitted to the recorder 3 through a suitable flexible cable 124, which also is is provided with a plug type terminal 125 for easy connection with a corresponding socket in the recorder. Where a recorder 3 is provided with various types of automatic controls which are responsive to certain conditions indicated by the recorder, suitable electrical signals are adapted to be transmitted from the recorder 3 to the remote control box 2 through a suitable flexible cable 126, which is connected to the recorder through a plug type terminal 127. Where desired, both ends of the cables 122, 124, and 126 may be provided with plug type terminals, although in most instances it will be sufiicient if only one end of these cables is provided with a plug type terminal While the other end of the cable is permanently connected to the electrical circuits of the filament puller 1, the remote control box 2, or the recorder 3.

I When it is desired to operate the tensile tester, the main switch S is closed and the motor switch S also is closed, thereby connecting one terminal 128 of the motor M to the line L The drive motor M preferably is of the reversible synchronous type and is provided with terminals 129 and 129 which are alternately adapted to be energized in addition to the terminal 128 to provide for opposite directions of rotation of the drive motor. These terminals 129 and 129' of the motor are adapted to be connected to the other side L of the power supply through a motor direction relay Ry A condenser C is connected across the motor winding terminals 129 and 129 so as to produce the desired phase shift for riving the motor in the desired manner.

The exciting windings of both the extension yoke clutch GL and the elongation measuring potentiometer clutch GL are direct current windings and therefore are adapted to be connected to the alternating current source of supply through a suitable rectifier circuit. A terminal 131 of the clutch GL and a terminal 132 of the clutch GL are adapted to be connected to the line L of the source of electrical power through the main switch S and a second terminal 133 of the clutch GL and 134 of the clutch CL are adapted to be connected respectively through a master relay Ry and an elongation potentiometer clutch relay Ry to the rectifier circuit. The illusrated rectifier circuit includes a resistor RS and a rectifier D adapted to be connected to line L of the source of electric power supply through the main switch S Condensers C and C are connected to opposite ends of the resistor RS and are adapted to be connected to line L of the source of electrical power supply through the main switch S In this manner all of the electrical energization of the driving parts of the filament puller can be supplied from a single source of alternating current electrical power supply through the main switch S A tensile tester made in accordance with the present .inv fi'tion is particularly adaptable for testing specimens under various environmental conditions. The flexible cables 122 and 124 which provide the electrical connections between the filament puller 1 and respectively the remote control box 2 and the recorder 3 facilitate the arrangement of the filament puller within an environ- ..mental control cabinet wherein the temperature and fluid surrounding the test specimen can be accurately controlled. Furthermore, the parts of the filament puller 14 which hold the ends of a test specimen and which are adapted to be moved relative to each other for varying the tension in the specimen preferably are made of suitable non-corrosive material, such as stainless steel, so that tensile tests of specimens can be conducted with the specimen completely immersed in any desired liquid, such as water 135, in a suitable receptacle 136.

In order to facilitate the placement of a test specimen in a container, such as the water receptacle 136, the filament puller housing 33 is'adjustably mounted on a supporting post 137 preferably rigidly secured to a suitable base 138. The filament puller housing 33 is adjustably mounted on the post 137 by a pair of suitable brackets 139, which provide for ready adjustment of the vertical position of the filament puller to facilitate placing a test specimen 4 in an environmental container.

In order to perform a complete tensile test of a speci men filament, the first step is to determine the den'ier of the filament in any suitable manner. The denier potentiometer R then is set by adjusting the potentiometer dial 29 to the denier of the sample filament, and the filament is mounted on the filament puller 1 between the strain gage tension bar hook 9 and the extension yoke claws 16. The filament puller 1 or the specimen-holding parts thereof are then placed in the desired environment for conducting the test, after which the main power switch S and the motor switch S are closed. A motor pilot light LM on the remote control box is lit when the motor power switch S is closed, thus indicating that the motor is in condition for driving the extension yoke of the filament puller to start a tensile test of the specimen.

The test may be begun by depressing the button of a starting switch S This switch comprises a contactor 140 which is adapted to close an energizing circuit from the power line L through a set of contacts 141 so as to energize an exciting winding 142 of the double-acting solenoid air valve A which controls the air supply to the extension yoke quick-return cylinder 77. The other side of the solenoid valve exciting winding 142 is connected directly to the other line L through the main switch S This causes the solenoid valve A to move to its upper position as shown in FIG. 2, thereby closing the vent 86 of the air cylinder 77 and connecting this cylinder to the air pressure supply 85. This assures that the extension yoke 20 is fully returned to its initial or zero starting position and places a reverse torque on the driven member of the crown tooth portion of the extension yoke clutch GL through the gear 65 and the main drive shaft 63. This is desirable as it assures a positive mechanical engagement of the mechanical drive through the crown tooth portion of the extension yoke clutch and avoids the possibility of slippage therethrough. I

The starting switch S also comprises a second contactor 143 which closes a circuit through contacts which connect the power line L to an exciting winding 144 of the master relay Ry so as to energize this winding and actuate this relay. Energization of the master relay closes a series of circuits through three contactors 145, 146,

and 147. The contactor 146 closes the circuit between the terminal 133 of the extension yoke clutch CL and the rectifier, thereby energizing the exciting winding of this clutch which tends to drive the extension yoke 20 downwardly through the main drive shaft 63, the gear 65, and the gear rack 66. This driving force on the extension yoke 20 is resisted by the air pressure in the cylinder 77 on the piston 74 at the upper end of the extension yoke 20 and further assures a positive mechanical driving connection through the crown tooth portion of the clutch GL This action usually will be only momentary in nature as pressure on the button of the starting switch S normally is of short duration, just sufiicient to obtain energization of the master relay exciting winding 144 and of the double-acting solenoid air valve coil 142.

Release of the starting switch button opens the circuits through the starting switch contactors 140 and 143. This deenergizes the double-acting solenoid air valve coil 142 through the contactor 14) and releases the magnetic actuation of the solenoid air valve which is then mechanically returned by any suitable means, as by a spring, to the position shown in FIG. 2, wherein the quick-return air cylinder 77 is vented through the solenoid air valve and the vent 86. 7

As soon as the master relay Ry exciting Winding 144 is energized after the starting switch S has been closed, the master relay contactor 147 closes a holding circuit which is adapted to maintain energization of its exciting winding 144- after'the starting switch S has been released. This holdingcircuit includes a series of circuit opening and closing switches which are responsive to various conditions for controlling the operation of the master relay and are normally in closed position at the time that the master relay winding 14-4 is initially energized by the starting switch. In this manner the exciting winding of the extension yoke clutch GL is energized through the rectifier D and the master relay contactor 146, so that the extension yoke is driven by the drive motor M in a direction which will tend to exert tension on a specimen filament 4 mounted between the strain gage 12 and the extension yoke base holding member 14.

As soon as the extension yoke 20 has begun its downward travel, an upper limit microswitch S7 is actuated to its closed circuit position so as to energize a circuit extending through this upper limit switch to master relay contacts 148 which are closed through the master contactor 145. This circuit extends to the recorder and is connected to a microswitch S which normally is opencircuited at the initial stages of operation of the extension yoke 20.

Further downward movement of the extension yoke 20 under actuation of the drive motor M causes the specimen-holding base member 14 to take up any slack in the test specimen 4 and eventually to place stress thereon. When the specimen 4 is stressed, the tension therein is transmitted as a force through the tension bar 11 to the strain gage 12, so that an electrical signal is transmitted from the strain gage over conductors 27 to the Y -axis drive control 28 of the recorder. This operates the conventional servo-motor recorder controls to provide energization of a servo-motor 149 through suitable conductors 150 connected to the remote control box 2 and through this box to the source of electrical power supply L -L This causes the servo-motor 149 to drive a recorder roll 151 through suitable mechanical connections thereto to provde for movement of two-coordinate paper relative to the Y-axis of the paper. The servo-motor 149 could be used to drive any suitable two-coordinate paper holder in the Y-axis of the paper and, in some instances, such a holder might comprise a hat table. For illustrative purposes, the present invention is shown in connection with a roll type paper holder of a conventional X-Y recorder 3, similar to that illustrated and described in Patents 2,464,708 and 2,835,858-Moseley. Such recording instruments also are illustrated and described in a publication by the L. F. Moseley Company in a manual entitled Autograf XY Recorder.

All such recorders are provided with certain basic features, such as the pen 113 of any suitable type for drawing a curve on coordinate draft paper mounted on the paper holder of the recorder. The pen 113 is adapted to move relative to the coordinate paper in two different directions, generally indicated as the X and Y coordinate axes of the paper. In certain types of recorders, the paper may be held stationary and the pen moved relative thereto in both directions. In other types of XY recorders, such as that illustrated, the coordinate paper is driven in one direction by a se1vo-motor, such as the servo-motor 149, and the pen 113 is driven along the other axis by another servo-motor, such as the servo-motor 112. In this .the remote control box and manner, a curve drawn on coordinate paper by the pen 113 in response to the relative movement between the paper holder and the pen gives a definite relationship to the X and Y axes of the paper which bears a direct relationship to the signals received from external sources by the X and Y axis drive controls. The Y axis relationship in the illustrated system is provided by the electrical signal received by the recorder from the strain gage 12 over the conductors 27, and the X-axis relationship is provided by electrical signals supplied to the recorder from the elongation measuring potentiometer 93 over conductors 198 and M29.

Since the movement of the yoke 2t? from its initial or zero position to the position of the base 14 when it initially places stress on a specimen filament 14 may vary slightly with different specimens, and since different specimens may have slightly erratic initial strain characteristics at relatively low stress resulting from various causes, such as crimp or other slight non-uniform physical configurations of specimens, it is desirable that the stress-strain curves recorded on the coordinate paper should, where possible, eliminate such initial erratic portions and thereby provide stress-strain curves which can be more readily compared. This can conveniently be done by using circuitry which will prevent recordation of stress-strain results until the stress on a test specimen reaches a predetermined minimum value. It has been found that for most single fibers the erratic portions of stress-strain curve occur below 2 percent stress on the specimens. Thus, by eliminating the recordation of strain of test specimens below 2 percent stress, the desired stress-strain curves can be recorded by the recorder pen 113, and the curves then may be extrapolated to indicate the normal stress-strain relationships which would occur below this 2 percent stress.

A very simple manner of obtaining a cut-ofi of the strain during the initial 2 percent stress on a test specimen is to mount a microswitch S in the circuit which is responsive to the stress on the test specimen, and arranging this'microswitch S so that it will remain open below percent stress on the test specimen and will close a circuit above this predetermined minimum stress, so as to 1nit1ate recordation of the strain. In a system such as that illustrated in the drawings, wherein the stress is plotted on the stress-strain coordinate paper along the Y- axis, the microswitch S can conveniently be placed on the recorder in a position so that it can be actuated by the operation of the recorder to a 2 percent stress position. In the conventional recorder provided with a roll 15l on which the coordinate paper is mounted and in which the angular position of the roll 151 indicates the Y coordinate or stress, it has been found very convenient simply to mount the microswitch S adjacent to an end of the roll 151 and operable by it. This can readily be done by arranging an operating finger 152 of the microswitch in a position engageable by an element of the roll 151 such that when the roll 15]; has moved from its zero position through an angle corresponding to 2 percent stress, the microswitch S will close an electrical circuitwhich will initiate the indication and recordation of stra n ot the test specimen, This strain indicating initiatlngcircuit is easily traced by reference to FIG. 2 as extending from the source of electrical power L through the switch S to the upper rack limit microswitch S through this switch to the master relay contacts 148 and its contactor 145, through the recorder 2 percent strain microswitch S to an excitlng winding 153 of an elongation potentiometer clutch relay Ry to power line L This energizes relay Ry and closes a circuit through its contactor 154 which energizes the exciting winding of the elongation potentiometer clutch GL through the rectifier D thereby providing for mechanically driving the elongation potentiometer contactor 110. This energization is indicated to the test operator by energization of a pilot light LM on the remote control box 2, which is connected in parallel with the relay winding 153. In this manner, the potentiometer contactor 110 will be moved proportional to the rotation of the main drive shaft 63 and therefore proportional to the actuation of the extension yoke gear rack 66 when the clutch GL is energized, thus providing a direct relationship between the voltage across the potentiometer 98 and the strain on the test specimen 4 for strain of the test specimen over 2 percent stress thereon. Thus, the recorder pen 113 of the illustrated recorder 3 will be moved along a supporting guide bar 155 by the servomotor 112 in direct proportion to the strain on a test specimen above 2 percent stress, and strain will be indicated by the curve recorded by the pen on the coordinate paper mounted on the recorder roll 151.

In order to protect the tensile tester against accidental damage due to various factors which might cause certain parts of the tensile tester to be operated beyond predetermined maximum safe limits of operation, a series of operational limit switches are included in the control circuitry. These limit switches may be generally arranged in a series circuit which is adapted to deenergize the holding circuit of the master relay R372 when any of the limiting conditions is reached. This operational limiting holding circuit preferably comprises switches which are operable for deenergization of the master relay Ry to provide for initiation of the quick-return operation of the extension yoke 20 in response to full extension of the extension yoke, to full 100 percent operation of the elongatin measuring potentiometer 98, to a decrease in tension of the test specimen 4 as indicated by the tension indicating operation of the recorder roll 151, such as when a stress reversal occurs due to the breaking of a test specimen, to full scale operation of the stress indicating recording pen 113 by its movement to the end of the pen guide bar 155, and to a normally closed manually operable control.

Specifically, this safety operational limit circuit may conveniently include a normally closed microswitch S which is arranged to be operable by the extension yoke to open this circuit when the extension yoke has moved to its maximum lower 100 percent rack limit position. This lower rack limit microswitch S may be of any suitable type and may include an operating finger 156 which is engageable by a part of the extension yoke to open this normally closed microswitch at the lower limit of the extension yoke rack movement. The operational limit circuit can extend from the lower rack limit microswitch S to a normally closed microswitch S which is adapted to be opened in response to full 100 percent operation of the elongation measuring potentiometer 110. This 100 percent potentiometer position limiting switch normally is held in closed circuit position and may conveniently be operated to open-circuit position by a cam 157 drivingly mounted on the potentiometer shaft 105 and arranged in engagement with a switch operating finger 157'. The operational limit circuit may then extend from the microswitch S in the filament puller to a microswitch S on the recorder, which is adapted to be maintained in closed circuit position during forward drive of the recorder roll 115. This position of the microswitch S may conveniently be made responsive to the direction of drive of the roll 115 by arranging an operating finger 158 of the microswitch S in engagement with a friction operating surface 159 on the roll 151, so that forward drive of the roll 151 biases the switch S to closed circuit position. This switch S readily serves to stop the normal operation of the tensile test when a stress reversal is indicated on the recorder 3 by a reverse rotation of the roll 151. Since a stress reversal will be indicated when a conventional tensile test is completed on the rupture of a test specimen 4, the recorder roll will tend to be rotated in a reverse direction and the friction surface 159 will bias the microswitch finger 158 so as to open the microswitch S The operational limit circuit also can be used to protect the recorder against an attempt to continue a tensile test beyond the recording limits of the instrument by arranging a normally closed microswitch S connected in series with the stress reversal microswitch S This microswitch S is readily operable to open-circuit position by arranging an operating finger 160 thereof for engagement by a portion of the recording pen 113 when the operating pen reaches its full scale deflection at the end of its guide bar 155.

In order to assure against possible damage to the tensile tester due to unforeseen circumstances, the operation- 211 limit holding circuit for the master relay Ry preferably also includes a normally closed manually operable switch S connected in series with the various operational limiting microswitches. This manually operable safety switch S preferably is arranged in the remote control box 2 in a position nearest to the operator of the tensile tester, and in series with the master relay holding circuit contacts which are adapted to be closed by the contactor 147.

In this manner, whenever one of the four specified limiting conditions occurs or the manually operable switch S is opened, the holding circuit of the master relay Ry will be opened so as to deenergize the master relay exciting winding 144. Deenergization of the exciting winding 144 causes the master relay contactor-s 147 and 146 respectively to open the holding circuit of the relay exciting winding 144 and the energizing circuit of the extension yoke clutch CL and to open the circuit between the master relay contacts 148 through the contactor 145. Opening of these circuits respectively provides for mechanically disconnecting the drive between the drive mo tor M and the extension yoke 20 through the extension yoke clutch GL which stops further extension of the filament puller; opening of the holding circuit through the master relay contactor 147, which prevents reenergization of the extension yoke clutch 0L except under direct manual control by a manually operable switch, such as the manually operable starting switch S or some other manually operable switch for controlling the perfomance of hysteresis tests.

Opening of the circuit through the master relay contacts 148 by its contactor 145 removes the control of energization of the elongation potentiometer relay exciting winding 153 from the master relay, so that this relay Ry would be opened if its exciting winding 153 were not provided with a holding circuit. Such a holding circuit for the elongation potentiometer clutch relay is desirable, as the elongation potentiometer contactor should be returned to its Zero position after a tensile test has been completed, so that it will be ready for the indication of the strain on a test specimen when another test is begun. Such a holding circuit for the exciting winding 153 of the relay Ry is provided through a normally closed manually operable switch S a contactor 161 of the relay Ry and an elongation potentiometer zero position limit microswitch S This holding circuit is closed when the relay exciting winding 153 is energized and the elongation measuring potentiometer contactor 110 moves away from its zero position.

In order to obtain the safety control feature of this holding circuit, the potentiometer zero position microswitch S may conveniently be provided with an operating finger 162 arranged in engagement with an operating cam 163 drivingly mounted on the potentiometer shaft 105, which is constructed and arranged to open the microswitch S when the elongation potentiometer is in its zero position and to close it for all other positions of the potentiometer.

Whenever the master relay exciting winding 144 is deenergized in response to any of the operational limiting conditions or by the manually operable switch S the master relay contactor closes the circuit through contacts 164. This normally will occur at a time when the extension yoke 20 is moved downwardly from its zero extension position, so that the microswitch S is in its closed circuit position, thereby providing an energizing circuit through the switch S the contactor 145, and contacts 164 for the two-way solenoid air valve energizing winding 142. This actuates the air valve 83 to its upper position as viewed in FIG. 2, so as to close communication between the vent 66 and the quick-return cylinder 77 and provide air pressure into the cylinder 77 through the valve 83 from the air supply 85. This serves 'to provide for a quick retraction of the extension yoke 2t? by the quick-return piston 74, as has been previously explained. Retraction of the extension yoke in this manner causes the reverse rotation of the drive gear 65 by the upward movement of the extension yoke gear rack 66, and thus causes the main drive shaft 63 to rotate in the reverse direction from its normal forward operation. This reverse rotation of the main drive shaft 63 is transmitted through the elongation potentiometer clutch GL to the potentiometer shaft 1%, so as to return the potentiometer contactor 11% to its zero or initial starting position.

In most instances it will be found that the elongation potentiometer contactor 110 will be returned to its initial or zero position, shown in FIG. 2, before the extension yoke 20 reaches its initial or zero position, also shown in this figure, for the reason that the potentiometer contactor 110 will not have been driven from its zero position until after the extension yoke 20 has traveled downwardly so as to apply a predetermined stress, such as 2 percent stress, on a test specimen. It, therefore, will be returned to its zero position correspondingly sooner than will the extension yoke 20. In order to prevent damage to the elongation measuring potentiometer, it therefore becomes necessary to stop the drive of the potentiometer contactor 114) prior to the complete return of the extension yoke 20 to its zero position. This can readily be accomplished through the zero position limit microswitch S which, as has been explained, is actuated to its closed position by the cam 163 mounted on the potentiometer shaft 105 for all positions of the elongation potentiometer contactor 110 except when this contactor 110 is in its zero position. In this zero position of the contactor 110, the cam 163 actuates the microswitch S through its finger 162 to open-circuit position, which deenergizes the holding circuit for the elongation potentiometer clutch relay exciting winding 153, causing this relay Ry to open. This opens the energizing circuit of the exciting winding for the elongation potentiometer clutch CL and declutches the drive between the elongation potentiometer contactor 110 and the main drive shaft 63. This immediately stops the rotation of the elongation potentiometer contactor 110 in its zero position and allows the free travel of the extension yoke to continue to its initial or zero position under the operation of the quick-return piston 74. When the extension yoke 20 reaches its zero position, a suitable element on the extension yoke, which may comprise an operating finger 165, engages a finger 166 of the upper rack limit microswitch S and biases it to open-circuit position, thereby opening the energizing circuit of the double-acting solenoid air valve exciting winding 142 to end the retracting of the extension yoke.

The actuation of the elongation measuring potentiometer may be brought under manual control at any time while the extension yoke is actuated away from its zero or upper rack limiting position through the normally closed elongation potentiometer clutch manual stop switch S simply by depressing this switch, which opens the holding circuit of the elongation potentiometer clutch relay exciting winding 153 and causes this relay Ry to open so as to open the energizing circuit of the elongation potentiometer clutch CL Drive of the elongation potentiometer contactor 110 may similarly be manually started by closing a circuit for energizing the elongation potentiometer clutch relay winding 153 by depressing an operating button of a normally open elongation potentiometer clutch manual starting switch $16, so

2% as to close a circuit which energizes the exciting winding 153 of the elongation potentiometer clutch relay Ry This energization of the exciting winding 153 of the relay Ry closes the relay contactor 154 across relay contacts which energize the exciting winding of the elongation potentiometer clutch CL so as to provide a driving connection of the elongation potentiometer contact with the main drive shaft 63. In this manner, operation of the elongation measuring potentiometer may be brought under manual control by the manual start and stop switches S and S respectively. 7

Under certain circumstances, it may be desirable to stop a tensile test at a predetermined point and to return the extension yoke to its zero position. This can be readily done by manually disconnecting the holding circuit of the master relay exciting Winding 144 by depressing the push button of the manually operable switch S When this siwtch S is open-circuited, it opens the holding circuit of the master relay Ry as has been explained, to energize the double-acting solenoid air valve coil 142 and provide for the quick-return retraction of the extension yoke 20 in the normal manner.

In addition to the usual tensile test for determining the modulus of elasticity, yield point, and ultimate strength of test specimens, it is desirable at times to obtain tensile hysteresis characteristics of test specimens. The present invention is particularly adaptable to provide for obtaining such tests either automatically or manuall and for varying the maximum stress applied to a specimen in performing such tests. This is readily obtained by controlling the energization and deenergization of the motor direction relay Ry either automatically by the recorder R or by suitable manual push button switches.

The motor direction relay is adapted to connect the drive motor terminals 129 and 129' alternately to the power line L through the motor direction relay contactor 130 to provide for opposite directions of rotation. This relay contactor 130 is adapted to close a circuit through relay contacts 167 for energization of the drive motor M through its terminal 129 when the motor direction relay exciting winding 168 is deenergized, as shown in FIG. 2, to provide for motor operation in a forward direction; that is, in a direction which will advance or lower the extension yoke 20 under normal driving engagement of the various gears and clutches. This is the normal position for the motor direction relay for the performance of tensile tests and can be used for manually placing stress on a test specimen 4 in the performance of a tensile hysteresis test.

In order to perform a tensile hysteresis test, the stress reversal microswitch S is shunted out of circuit by a switch S This renders inoperative the quick return of the extension yoke 20 due to stress reversal as indicated by reverse drive of the recorder roll 151. Manual hysteresis tests are readily performed by initially placing stress on a test specimen simply by depressing the starting switch S as for the commencement of a normal tensile test, and, when the desired maximum stress has been placed on the test specimen, as indicated by the pen 113 on the recorder 3, a normally open manually operable switch S in the remote control box is operated to its closed position by depressing its operating button. This completes a circuit through contactor 159 and contacts 170 of the switch S so as to energize the motor director relay exciting Winding 168. This actuates the motor direction relay Ry so as to close a reverse drive motor circuit through the motor direction relay contactor 130 and contacts 171, while opening the motor circuit through contacts 167. This position of the motor direction relay Ry energizes the drive motor M through its terminal 129' for operation of the drive motor in reverse; that is, in a direction which will retract the extension yoke 20 upwardly through the drive gear 65 and the main drive shaft 63. Such retraction of the extension yoke 20 by the drive motor M in no way provides for quick return of the extension yoke 20 through its air piston 74. It simply relieves the stress on a test specimen 4 at the same slow rate as the stress was initially applied to the test specimen, thereby preventing any suddent changes in the stress on the specimen. When the stress on the test specimen 4 has been reduced to zero, the hysteresis test may be continued by again stressing the test specimen simply by releasing pressure on the normally open manual switch S so as to open the circuit through its contacts 170, thereby deenergizing the motor direction relay exciting winding 168 and returning this relay to the position shown in FIG. 2. In this position, the relay contactor 130 again closes the drive motor energizing circuit through the relay contacts 167 and the motor terminal 129 for forward drive of the drive motor and downward actuation of the extension yoke 20. In this manner, a test specimen 4 may be repetitively stressed and relieved of stress or relieved of such portion of the stress as may be desired and restressed to a higher or lower value during repeated stressing thereof to obtain the characteristics of the specimen by such hysteresis tests.

Hysteresis tests also may be useful for the determination of effects which can be produced in certain types of materials by stressing beyond the elastic limits of the material from repeated stressing above the elastic limit. All materials which are stressed to a value exceeding the elastic limit receive a deformation, some of which remains as a permanent set or elongation of the material after the stress has been removed. In the case of nonductile materials, overstressing of this type usually causes permanent injury, and a few repetitions of such loading often is sufficient to cause rupture of the stressed element.

In some instances, if the material is stressed beyond the yield point, and the stress then relieved substantially, a restressing will show that the yield point has been raised and the deformation above the yield point is decreased. In most instances, stress-strain tests of this type are computed in terms of the original cross sectional area of a test specimen. In the illustrated apparatus, the recorder 3 will indicate the stress-strain relationship in terms of unit cross sectional area, but this will not be strictly accurate above the yield point, as the signal received by the recorder is proportional to the unit cross sectional area on the basis only of the original cross section of a test specimen as set by the denier potentiometer R Actually the new yield point of a material, which has been given a permanent deformation by having been stressed beyond a yield point and then having the stress reduced substantially and then restressed, would be higher than the value which will be indicated by the recorder, as it is not practical to determine the cross sectional area of a test specimen during a hysteresis test or during a test with repeated stressing beyond the yield point of the material. If accurate indication of the new yield point is to be given, the denier potentiometer dial 29 on the remote control box 2 should be reset after each stressing of the specimen beyond its yield point, as the permanent deformation acquired by the specimen not only includes a permanent elongation or strain, but also includes a permanent reduction in the cross sectional area, so that the stress per unit area actually is higher than that indicated in terms of the original area of the test specimen.

Hysteresis tests of the type which have already been described can also be obtained automatically by the use of certain limit switches in the recorder for automatically reversing the drive motor M at a predetermined stress. Below the elastic limit the stress is proportional to the strain, so that the reversal of the drive motor at a predetermined strain, as indicated by the strain of a test specimen below the elastic limit, and the automatic restressing of the specimen when the strain thereof has been reduced to zero will provide the desired automatic hysteresis test. This may conveniently be done by atranging a normally open microswitch S adjustably mounted with reference to the recorder pen 113 and provided with an operating finger I72 engageable by a part of the pen 113, as by an operating button 173 on the pen finger 119. The microswitch S may be slidably mounted on a supporting bar 174, parallel to the pen guide bar 155, so that the switch S can be set for operation to its closed position by engagement thereof by the recorder pen button 173 at any predetermined strain of a test specimen as indicated by the position of the recorder pen 113. The microswitch S is connected in a circuit extending from the power supply line L to a terminal of the exciting winding 168 of the motor direction relay Ry so as to energize this exciting winding when the switch S is closed. Energization of the winding 168 actuates the motor direction relay Ry so as to open the circuit of the drive motor M from its terminal 129 through the relay contactor 134) and contacts 167 and closes an energizing circuit for the drive motor M through its terminal 129, the contactor 130, and contacts 171, thereby reversing the direction of rotation of the drive motor M This results in a gradual reversal of the stress on the test specimen, as the operation of the quick return of the extension yoke 20 by the air piston 74 is rendered inoperative by the shunting of the stress reversal microswitch S through the switch S for all hysteresis tests.

In this position of the motor direction relay Ry a holding circuit for maintaining energization of the relay exciting winding 168 is provided through a relay contactor 1'75, which closes the circuit through relay contacts 176, a normally closed push button switch S and a normally closed zero strain microswitch S If it is desired to stop the stress reducing part of the test before the strain has been reduced to zero and automatically to restress the specimen, this can easily be done by simply depressing the push button of the manually operable switch S on the remote control box 2, so as to deenergize the relay exciting winding 168 through its holding circuit. This holding circuit normally will be broken by the zero strain microswitch S in the recorder by engagement of an operating finger 177 of the microswitch S by the pen 113 when it is returned to its zero strain position.

In this manner the hysteresis characteristics of a specimen may be easily determined automatically by presetting the adjustable microswitch S to the desired maximum strain on a specimen, with the stress reversal microswitch S shunted by closure of the switch S then automatically starting the test by closing the starting switch S Closure of starting switch S causes the drive motor M to be operated in a forward direction in the usual manner, so as to provide for downward actuation of the extension yoke 20 for the application of stress on a test specimen 4 mounted on the filament puller 1. The recorder 3 will record the stress-strain relationship of the test in the usual manner until the recorder pen 113 actuates normally open microswitch S to closed position, so as to energize the exciting winding 168 of the motor direction relay Ry to provide for reverse drive of the drive motor M as has been explained. The automatic repetition of the stressing and reduction of stress of the test specimen will continue between the zero strain position and the predetermined maximum strain position as set by the limit switch S until the test specimen 4 is fractured or until the test is stopped by opening of switch S or S on the remote control box.

In this manner, automatic hysteresis tests, as well as manual hysteresis tests, may be readily obtained by the illustrated embodiment of the present invention, in addition to direct stress-strain characteristic tensile tests, and all such tests can be conducted with an apparatus which is adapted to perform these tests on specimens in ambients arseaes 23 which may be controlled as to both temperature and humidity or other fluid environments.

While a particular embodiment of this invention has been illustrated and described, modifications thereof will occur to those skilled in the art. It is to be understood, therefore, that this invention is not to be limited to the particular details disclosed, and it is intended in the appended claims to cover all modifications Within the spirit and scope of this invention.

What is claimed is:

1. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for tensioning a specimen held by said holding means including a reversible drive; means for indicating tension on a specimen; means for indicating elongation of a specimen; a quick-return retraction drive means for said tensioning means independent of said reversible drive; a normally-closed manual control means of said quickreturn retraction drive means; and means for initiating operation of said quick-return means in response to full extension of said tensioning means, to decrease in tension on a specimen, to full scale operation of said tension indicating means, and to opening of said nornially-closed manual control means.

2. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means including an extension yoke with a reversible motor drive for tensioning a specimen held by said holding means; means for indicating tension on a specimen; means for indicating elongation of a specimen; a quick-return retraction drive means for said extension yoke independent of said drive motor; a normally-closed manual control means for said quick-return retraction drive means; and means for initiating operation of said extension yoke quick-return means in response to full extension of said extension yoke, to decrease in tension as indicated by said tension indicating means, to full scale operationof said tension indicating means, and to opening of said normally-closed manual control means.

3. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for tensioning a specimen held by said holding means, said tensioning means including an extension yoke with a reversible drive motor, means for indicating tension on a specimen; means for indicating elongation of a specimen; and means for obtaining tension hysteresis characteristics of a specimen including automatic and manual controls, said automatic controls comprising means responsive to a variable predetermined maximum tension indication by said tension indicating means for energizing said motor for reverse drive and means responsive to zero tension indication for energizing said motor for tensioning for- Ward drive, said manual controls comprising manually operable means for energizing said motor in opposite drive directions.

4. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means including an extension yoke With a reversible motor drive for tensioning a specimen held by said holding means; means for indicating tension on a specimen; means for indicating elongation of a specimen; a quick-return re-.

traction drive means for said extension yoke independent of said drive motor comprising an air cylinder having a piston therein connected to said extension yoke, means for supplying air pressure to said cylinder on one side of said piston for retraction drive thereof, a vent in said cylinder on the side of said piston away from the air pressure side thereof, means for controlling the supply of air pressure to said cylinder and for venting said cylinder on the air-pressure side of said piston; a normally-closed manual;

control means for said quick-return retraction drive means;

and means for initiating operation of said extension yoke quick-return means in response to full extension of said extension yoke, to decrease in tension as indicated by said tension indicating means, to full scale operation of said tension indicating means, and to opening of said normallyclosed manual control means.

5. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for tensioning a specimen held by said holding means, said tensioning means including an extension yoke with a reversible drive motor, means for indicating tension on a specimen; means for indicating elongation of a specimen; means for obtaining tension hysteresis characteristics of a specimen including automatic and manual controls, said automatic controls comprising means responsive to a variable predetermined maximum tension indication by said tension indicating means for energizing said motor for reverse drive and means responsive to zero tension indication for energizing said motor for tensioning forward drive; said manual controls comprising manually operable means for energizing said motor in opposite drive directions; a quick-return retraction drive means for said extension yoke independent of said drive motor; a normally-closed manual control means for said quick-return retraction drive means; means for initiating operation of said extension yoke quick-return means in response to full extension of said extension yoke, to decrease in tension as indicated by said tension indicating means, to full scale operation of said tension indicating means, and to opening of said normally-closed manual control means; and means for rendering inoperative said quick-return means response to said indication of decrease in tension when said apparatus is under control of said tension hysteresis characteristics means controls.

6. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for moving said specimen holding means relative to each other for varying the tension in the specimen including an extension yoke with a reversible drive means, a reversible drive motor, means for providing a driving connection between said drive motor and said extension yoke; means for controlling said driving connection including a master relay and a normallyopen manually-operable starting switch for initially energizing said master relay on closure of contacts of said starting switch, means for measuring tension on a specimen; means (TIM) responsive to measurments of said tension measuring means for indicating said tension measurements; means for measuring elongation of a specimen; means (EIM) resopnsive to measurements of said elongation-measuring means for indicating said elongation measurements; a quick-return retraction drive means for said extension yoke independent of said drive motor; means providing a holding circuit including contacts of said master relay adapted to be closed on energization of said master relay for normally maintaining energization of said master relay after initial energization thereof by said starting switch; a normally-closed manual control means in said holding circuit; said master relay holding circuit means comprising means operable for deenergization of said master relay to provide for operation of said extension yoke quick-return means in response to full extension of said extension yoke, to full operation of said elongation-measuring means, to decrease in tension as indicated by said TIM, to full scale operation of said TIM, and to opening of said normally-closed manual control means; said master relay having contacts adapted to close a circuit for energizing said quick-return drive means on deenergization of said master relay.

7. 'Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for moving said specimen holding means relative to each other for varying in the specimen including an extension yoke with a reversible drive means, a reversible drive motor, means for providing a driving connection between said drive motor and said extension yoke; means for controlling said driving connection including a master relay and a normally-open manually-operable starting switch for initially energizing said master relay on closure of contacts of said starting switch, means for indicating tension on a specimen; means for indicating elongation of a specimen; a quick-return retraction drive means for said extension yoke independent of said drive motor, said quick-return drive means comprising an air cylinder having a piston therein connected to said extension yoke, means including a two-way solenoid valve for controlling the supply of air pressure to said cylinder and for venting said cylinder on the air-pressure side of said piston; means providing a holding circuit including contacts of said master relay adapted to be closed on energization of said master relay for normally maintaining energization of said master relay after initial energization thereof by said starting switch; a normally-closed manual control means in said holding circuit; said master relay holding circuit means comprising means operable for deenergization of said master relay to provide for operation of said extension yoke quick-return means in response to full extension of said extension yoke, to decrease in tension as indicated by said tension indicating means, to full scale operation of said tension indicating means, and to opening of said normally-closed manual control means; and said master relay having contacts adapted to close a circuit for energizing said quick-return drive means on deenergization of said master relay.

8. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for moving said specimen holding means relative to each other for varying the tension in the specimen including an extension yoke with a reversible drive means comprising a reversible drive motor and means for providing a driving connection between said drive motor and said extension yoke; means for controlling said driving connection including a master relay and a normally-open manually-operable starting switch for initially energizing said master relay on closure of contacts of said starting switch, means for measuring tension on a specimen; means (TIM) responsive to measurements of said tension measuring means for indicating said tension measurements; means for measuring elongation of a specimen; means responsive to measurements of said elongation measuring means for indicating said elongation measurements; a quick-return retraction drive means for said extension yoke independent of said drive motor, said quick-return drive means comprising an air cylinder having a piston therein connected to said extension yoke, means including a two-way solenoid valve for controlling the supply of air pressure to said cylinder and for venting said cylinder on the air-pressure side of said piston; means providing a holding circuit including contacts of said master relay adapted to be closed on energization of said master relay for normally maintaining energization of said master relay after initial energization thereof by said starting switch; a normally-closed manual control means in said holding circuit; said master relay holding circuit means comprising means operable for deenergization of said master relay to provide for operation of said extension yoke quick-return means in response to full extension of said extension yoke, to full operation of said elongation measuring means, to decrease in tension as indicated by said TIM, to full scale operation of said TIM, and to opening of said normally-closed manual control means; said master relay having contacts adapted to close a circuit for energizing said quick-return drive means on deenergization of said master relay; and means for varying the response of said tension measuring means in accordance with the cross section of the specimen be- 26 ing tested for obtaining an indication of tension on a specimen in terms of stress.

9. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for tensioning a specimen held by said holding means including means for moving said holding means relative to each other; said moving means including an extension yoke with a reversible gear drive, a reversible drive motor, means including a main drive electromagnetic clutch (MDC) having positive clutching means for providing a driving connection between said drive motor and said gear drive; means for energizing said MDC including a master relay and a normally-open manually-operable starting switch for initially energizing said master relay, said master relay having contacts for closing an energizing circuit for said MDC on energization of said master relay and breaking said MDC energizing circuit on deenergization of said master relay; means for measuring tension on a specimen; means (TIM) responsive to measurements of said tension measuring means for indicating said tension measurements; means for measuring elongation of a specimen; means (EIM) responsive to measurements of said elongation measuring means for indicating said elongation measurements; a quick-return retraction drive means for said extension yoke independent of said drive motor comprising an air cylinder having a piston therein connected to said extension yoke, means for supplying air pressure to said cylinder on one side of said piston for retraction drive thereof, a vent in said cylinder on the side of said piston away from the air-pressure side thereof, means including a solenoid valve for controlling the supply of air pressure to said cylinder and for venting said cylinder on the airpressure side of said piston; and said starting switch having contacts for initially energizing said solenoid valve to air-pressure admitting position on closure of said switch prior to tensioning movement of said extension yoke for exerting a force resisting an extension drive through said MDC to assure positive initial engagement thereof; means providing a holding circuit including contacts of said master relay adapted to be closed on energization of said master relay for normally maintaining energization of said master relay after initial energization thereof by said starting switch; a normally-closed manual control means in said holding circuit; said master relay holding circuit means comprising means operable for deenergization of said master relay to initiate operation of said extension yoke quick-return means in response to full extension of said extension yoke, to full operation of. said elongation measuring means, to decrease in tension as indicated by said TIM, to full scale operation of said TIM, and to opening of said normally-closed manual control means; and said master relay having contacts for energizing said quick-return drive means on deenergization of said master relay.

10. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the speci men; means for moving said specimen holding means relative to each other for varying the tension in the specimen; said moving means including an extension yoke with a reversible gear drive, a reversible drive. motor, means including a main drive electromagnetic clutch (MDC) for providing a driving connection between said drive motor and said gear drive; means for energizing said MDC including a matser relay and a normally-open manually-operable starting switch for initially energizing said master relay on closure of contacts of said starting switch, said master relay having contacts for closing an energizing circuit for said MDC on energization of said master relay and breaking said MDC energizing circuit on deenergization of said master relay; means (TIM) responsive to the tensile force on a specimen for indicating said force per unit cross-sectional area; means responsive to elongation of a specimen for indicating said elongation; and means for automatically obtaining tension hysteresis characteristics of a specimen including means responsive to a variable predetermined maximum tension as indicated by said TIM for energizing said motor for reverse drive and means responsive to zero tension indication by said TIM for energizing said motor for forward tensioning drive whereby said motor is automatically alternately operated in opposite directions as determined by said maximum tension and zero tension indications of said TIM.

11. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for moving said specimen holding means relative to each other for varying the tension in the specimen; said moving means including an extension yoke with a reversible gear drive, a reversible drive motor, means including a main drive electromagnetic clutch (MDC) for providing a driving connection between said drive motor and said gear drive; means for energizing said MDC including a master relay and a normally-open manually-operable starting switch for initially energizing said master relay on closure of contacts of said starting switch, said master relay having contacts for closing an energizing circuit for said MDC on energization of said master relay and breaking said MDC energizing circuit on deenergization of said master relay; means for measuring tension on a specimen; means (TIM) responsive to measurements of said tension measuring means for indicating said tension measurements; means for measuring elongation of a specimen; means responsive to measurements of said elongation measuring means for indicating said elongation measurements; a quick-return retraction drive means for said extension yoke independent of said drive motor; means providing a holding circuit including contacts of said master relay adapted to be closed on energization of said master relay for normally maintaining energization of said master relay after initial energization thereof by said starting switch; a normallyclosed manual control means in said holding circuit; said master relay holding circuit means comprising means operable for deenergization of said master relay to provide for operation of said extension yoke quick-return means in response to full extension of said extension yoke, to full operation of said elongation measuring means, to decrease in tension as indicated by said TIM, to full scale operation of said TIM, and to opening of said normally-closed manual control means; and said master relay having contacts for energizing said quick-return drive means on deenergization of said master relay.

12. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for moving said specimen holding means relative to each other for varying the tension in the specimen; said moving means including an extension yoke with a reversible gear drive, a reversible drive motor, means including a main drive electromagnetic clutch (MDC) for providing a driving connection between said drive motor and said gear drive; means for energizing said MDC including a master relay and a normallyopen manually-operable starting switch for initially energizing said master relay on closure of contacts of said starting switch, said master relay having contacts for closing an energizing circuit for said MDC on energization of said master relay and breaking said MDC energizing circuit on deenergization of said master relay; means for measuring tension .on a specimen; means (TIM) responsive to measurements of said tension measuring means for indicating said tension measurements; means (EMP) for measuring elongation of a specimen; means responsive to measurements of said elongation measuring means for indicating said elongation measurements, means including an electromagnetic clutch for providing a driving connection between said extension yoke drive gear and said elongation-measuring means; means including a relay having contacts for energizing said elongation-measuring means clutch (EMC) when said EMC relay (EMCR) is energized; an EMCR initial energizing circuit including means responsive to a predetermined minimum tension on a specimen as indicated by said TIM serially connected with a normally-closed switch adapted to be opened in the fully retracted position of said extension yoke and contacts of said master relay adapted to beclosed and opened when said master relay is respectively energized and deenergized, means providing a holding circuit for maintaining energization of said EMCR including EMCR contacts adapted to be closed on energiaztion of said EMCR and a normallyclosed switch adapted to be opened in the zero position of said elongation-measuring means for deenergizing said EMCR; means for automatically obtaining tension hysteresis characteristics of a specimen including motor reversing switch means responsive to a variable predetermined maximum tension as indicated by said TIM for energizing said motor for reverse drive and means responsive to zero tension indication by said TIM for energizing said motor for tensioning forward drive whereby said motor is automatically alternately operated in opposite directions determined by said maximum tension and zero tension indications of said'TIM; a quick-return retraction drive means for said extension yoke independent of said drive motor connected to said extension yoke, means providing a holding circuit including contacts of said master relay adapted to be closed on energization of said master relay for normally maintaining energization of said master relay after initial energization thereof by said starting switch; a normally-closed manual control means in said holding circuit; said master relay holding circuit means comprising means operable for deenergization of said master relay to provide for operation of said extension yoke quick-return means in response to full extension of said extension yoke, to full operation of said EMP, to decrease in tension as indicated by said TIM, to full scale operation of said TIM, and to opening of said normally-closed manual control means; means for rendering inoperative said quick-return means response to said indication of decrease in tension when said appa' ratus is under control of said tension hysteresis characteristics means controls; and said master relay having contacts for energizing said quick-return drive means on deenergization of said master relay.

13. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for moving said specimen holding means relative to each other for varying the tension in the specimen; said moving means including an extension yoke with a reversible gear drive, a reversible drive motor, means including a main drive electromagnetic clutch (MDC) for providing a driving connection between said drive motor and said gear drive; means for energizing said MDC including a master relay and a normally-open manually operable starting switch for initially energizing said master relay on closure of contacts of said starting switch, said master relay having contacts for closing an energizing circuit for said MDC on energization of said master relay and breaking said MDC energizing circuit on deenergization of said master relay; means for measuring tension on a specimen; means (TIM) responsive to measurements of said tension measuring means for indicating said tension measurements; means for measuring elongation of a specimen; means responsive to measurements of said elongation-measuring means for indicating said elongation measurements; means including an electromagnetic clutch for providing a driving connection between said extension yoke drive gear and said elongation-measuring means; means including a relay having contacts for energizing said elongationmeasuring means clutch (EMC) when said EMC relay (EMCR) is energized; an EMCR initial energizing circuit including means responsive to a predetermined minimum tension on a specimen as indicated by said TIM serially connected with a normally-closed switch adapted to be opened in the fully retracted position of said extension yoke and contacts of said master relay adapted to be closed and opened when said master relay is respectively energized and deenergized, means providing a holding circuit for maintaining energization of said EMCR including EMCR contacts adapted to be closed on energization of said EMCR and a normally-closed switch adapted to be opened in the zero position of said elongation measuring means for deenergizing said EMCR; means for automatically obtaining tension hysteresis characteristics of a specimen including motor reversing switch means responsive to a variable predeterminable maximum tension as indicated by said TIM for initiating energization of said MDR with an MDR energization holding circuit comprising MDR contacts closed on energization of said MDR and a normally-closed manually-operable forward-drive switch means and a second motor forwarddrive switch means responsive to zero tension indication by said TIM for deenergizing said MDR whereby said drive motor is adapted to be automatically alternately operated in opposite directions as determined by said maximum tension and zero tension indicated by said TIM; a quick-return retraction drive means for said extension yoke independent of said drive motor comprising an air cylinder having a piston therein connected to sa d extension yoke, means for supplying air pressure to said cylinder on one side of said piston for retractlon drive thereof, a vent in said cylinder on the side of said piston away from the air pressure side thereof, means for controlling the supply of air pressure to said cylinder and for venting said cylinder on the air-pressure side of said piston; means providing a holding circuit including contacts of said master relay adapted to be closed on energization of said master relay for normally maintaining energization of said master relay after initial energization thereof by said starting switch; a normally-closed manual control means in said holding circuit; said master relay holding circuit means comprising means operable for deenergization of said master relay to initiate operation of said extension yoke quick-return means in response to full extension of said extension yoke, to full operation of said elongation-measuring means, to decrease in tension as indicated by said TIM, to full scale operation of said TIM, and to opening of said normallyclosed manual control means; means for rendering inoperative said quick-return means response to said indication of decrease in tension when said apparatus is under control of said tension hysteresis characteristics means controls; said master relay having contacts for energizing said quick-return drive means on deenergiaztion of said master relay; and means for varying the response of said tension measuring means in accordance with the cross section of the specimen being tested for obtaining an indication of tension on a specimen in terms of stress.

14. Apparatus for testing the tensile properties of specimens comprising means for holding one end of a specimen; other means for holding the other end of the specimen; means for moving said specimen holding means relative to each other for varying the tension in the specimen; said moving means including an extension yoke with a reversible gear drive, a reversible drive motor, means for energizing said drive motor including a manually operable switch and a motor direction relay control means (MDR), said MDR having contact means for connecting said motor for forward drive when said MDR is deenergized and contact means for connecting said motor for reverse drive when said MDR is energized, means including a main drive electromagnetic clutch (MDC) for providing a driving connection between said drive motor and said gear drive; means for energizing said MDC including a master relay and a normally-open manually-operable starting switch for initially energizing said master relay by closure of contacts of said starting switch, said master relay having contacts for closing an energizing circuit for said MDC on energization of said master relay and breaking said MDC energizing circuit on deenergization of said master relay; means for measuring tension on a specimen; means for varying measurement response of said tension measuring means in accordance with the cross section of a specimen being tested for obtaining a measurement of tension in terms of stress; means (TIM) responsive to measurements of said tension measuring means for indicating said tension measurements; means including a potentiometer for measuring elongation of a specimen; means responsive to measurements of said elongation-measuring means for indicating said elongation measurements; means including an electromagnetic clutch for providing a driving connection between said extension yoke drive gear and said elongation-measuring potentiometer (EMP); means including a relay having contacts for energizing said elongation-measuring potentiometer clutch (EMPC) when said EMPC relay (EMPCR) is energized; an EMPCR initial energizing circuit including means responsive to a predetermined minimum tension on a specimen as indicated by said TIM serially connected with a normally-closed switch adapted to be opened in the fully retracted position of said ex tension yoke and contacts of said master relay adapted to be closed and opened when said master relay is respectively energized and deenergized; means providing a holding circuit for maintaining energization of said EMPCR including EMPCR contacts adapted to be closed on energization of said EMPCR and a normally-closed cam-operated EMP zero-position switch adapted to be opened in the zero position of said EMP for deenergizing said EMPCR; a normally-closed manually-operable switch for opening said EMPCR holding circuit; means including a normally-open manually-operable switch for independently energizing said EMPCR; means for automatically obtaining tension hysteresis characteristics of a specimen including motor reversing switch means responsive to a variable predeterminable maximum tension as indicated by said TIM for initiating energization of said MDR with an MDR energization holding circuit comprising MDR contacts closed on energization of said MDR and a normally-closed manually-operable forward-drive switch means and a second motor forward-drive switch means responsive to zero tension indication by said TIM for deenergizing said MDR whereby said drive motor is adapted to be automatically alternately operated in opposite directions as determined by said maximum tension and zero tension indicated by said TIM; a normally-open manually-operable switch means for energizing said MDR for obtaining reverse motor drive; a quick-return retraction drive means for said extension yoke independent of said drive motor, said quick-return drive means comprising an air cylinder having a piston therein connected to said extension yoke, means for supplying air pressure to said cylinder on one side of said piston for retraction drive thereof, a vent in said cylinder on the side of said piston away from the air-pressure side thereof, means on said piston for reducing the venting action of said vent as said piston approaches the end of its air-pressure actuated retraction stroke for trapping a small amount of air as a cushion between said piston and the end of said cylinder, means including a two-way solenoid valve for controlling the supply of air pressure to said cylinder and for venting said cylinder on the air-pressure side of said piston; said starting switch having contacts for closing a circuit for initially energizing said solenoid valve to air-pressure admitting position on closure of said starting switch; means providing a holding circuit including contacts of said master relay adapted to be closed on energization of said master relay for normally maintaining energization of said master relay after initial energization thereof by said starting switch; a normally-closed

Claims

1. APPARATUS FOR TESTING THE TENSILE PROPERTIES OF SPECIMENS COMPRISING MEANS FOR HOLDING ONE END OF A SPECIMEN; OTHER MEANS FOR HOLDING THE OTHER END OF THE SPECIMEN; MEANS FOR TENSIONING A SPECIMEN HELD BY SAID HOLDING MEANS INCLUDING A REVERSIBLE DRIVE; MEANS FOR INDICATING TENSION ON A SPECIMEN; MEANS FOR INDICATING ELONGATION OF A SPECIMEN; A QUICK-RETURN RETRACTION DRIVE MEANS FOR SAID TENSIONING MEANS INDEPENDENT OF SAID REVERSIBLE DRIVE; A NORMALLY-CLOSED MANUAL CONTROL MEANS OF SAID QUICKRETURN RETRACTION DRIVE MEANS; AND MEANS FOR INITIATING OPERATION OF SAID QUICK-RETURN MEANS IN RESPONSE TO FULL EXTENSION OF SAID TENSIONING MEANS, TO DECREASE IN TENSION ON A SPECIMEN, TO FULL SCALE OPERATION OF SAID TENSION INDICATING MEANS, AND TO OPENING OF SAID NORMALLY-CLOSED MANUAL CONTROL MEANS.