GB2081457A

GB2081457A - A machine for testing materials

Info

Publication number: GB2081457A
Application number: GB8123224A
Authority: GB
Original assignee: Instron Holdings Ltd
Current assignee: Instron Holdings Ltd
Priority date: 1980-08-05
Filing date: 1981-07-28
Publication date: 1982-02-17
Also published as: GB2081457B

Abstract

A materials testing machine is modified to enable it to apply both low frequency major cycle loads and high frequency minor cycle loads to specimen 12 e.g. a gas turbine blade by including between the low frequency actuator 16 of the machine and a lower grip 11 for the specimen an electrodynamic high frequency vibrator 17, a spring unit 19 being interposed between the actuator and the vibrator. The spring unit 19 may be a rubber bag filled with gas under pressure or a system of coil springs. Compressive, tensile or a combination of tensile and compressive loads may be applied to the specimen by a suitably designed machine. A load cell 13 between the upper specimen grip 10 and the frame 14 measures the applied load. <IMAGE>

Description

SPECIFICATION A machine for testing materials Atypical machine for testing materials is shown in Figure 1 of the accompanying drawings. It includes upper and lower grips 10,11 for holding the specimen 12 to be tested, the upper grip being connected through a load cell 13 to the top member 14 of the machine frame and the lower grip being connected to a hydraulic or electric actuator 16 fixed to the machine frame.

In use of the machine the actuator 16 is caused by an electrical control system including a function generator to apply cyclic loading to the specimen, which may typically take the form A shown in Figure 2 which is a plot of load against time. A hydraulic actuator can only apply such cyclic loading A to the specimen at a relatively low frequency in the range, at most, of 100-200 Hz. It is sometimes required, however, to apply to the specimen not only such low frequency major cycle loads, but also minor cycle loads of much higher frequency unattainable hydraulically or electrically, such as are shown at B in Figure 2. A typical instance is the fatigue testing of gas turbine blades in which the amplitude of the major cycle loads may, for example, be of the order 5 tons and that of the minor cycle loads of the order of +1/2ton.

The invention provides for this by providing between the actuator and the lower grip an electrodynamic vibrator with a spring unit interposed between the actuator and the vibrator.

An electrodynamic vibrator is a well known piece of equipment and comprises a field coil surrounding a core of ferromagnetic material, a source of D.C. for energizing the field coil, a moving coil disposed in a gap between the field coil and the core, a table which extends upwardly from the moving coil and is guided to exclude torsional and transverse movement of the moving coil and permit vertical movement only of the moving coil and an amplifier for applying A.C. signals to the moving coil.

In normal use a test object to be subjected to vibration is clamped to the table of the vibrator but when the vibrator is included in a materials testing machine in accordance with the invention the table is attached to the lower grip.

The invention will now be further described with reference to the embodiments shown in Figures 3 to 6 of the accompanying drawings, in which: Figure 3 is a view similar to Figure 1 showing the known testing machine modified in accordance with the invention, and capable of applying compression loads to the specimen; Figure 4 is an enlarged view of a portion of the machine shown in Figure 3; Figure 5 is a view similar to Figure 4 showing a modification capable of applying tension loads to a specimen, and Figure 6 is a view again similar to Figure 4 and showing a further modification capable of applying both compression and tension loads to the specimen.

Like reference numerals denote like parts throughout the Figures.

In the embodiment of the invention shown in Figures 3 and 4 an electrodynamic vibrator 17 is interposed between the actuator 16 and the lower grip 11, the table 18 of the vibrator being connected to the lower end of the lower grip 11. As shown a pneumatic spring 19 is interposed between the actuator 16 and 17. This pneumatic spring consists of a rubber bag 20 filled with gas, preferably air, under pressure which is sandwiched between upper and lower metal plates 21,22 held within a generally C-shaped bracket 23 attached to the vibrator 17. The lower plate 22 is attached to the actuator 16.When the actuator 16 is not in operation the vibrator is relieved of load from the compressed gas in the bag 20 by the lower lips 24 of the bracket 23 but when the actuator 16 is in operation the plate 22 is lifted from these lips and the actuator 16 and the vibrator 17 can operate jointly on the specimen to subject it to major and minor load cycles of the kind shown in Figure 2.

The apparatus shown in Figures 3 and 4 is suitable when the actuator 16 is intended to apply compression loads to the specimen. When it is desired to apply tension loads the apparatus is modified as shown in Figure 5, the rubber bag 20 and the plates 21,22 being disposed between a framework 25 connected to the actuator 16 and bearing through the plate 21 on the top of the bag and another framework 26 bearing through the plate 22 on the bottom of the bag and connected to the vibrator 17, the sides of the framework 25 extending through apertures in the base of the framework 26. Compression of the pneumatic spring 19 therefore applies a tension force to the specimen instead of a compression force as in Figure 3.

Figure 6 shows a further modification capable of applying both compression and tension loads to the specimen and therefore operating through zero load.

It includes a framework 27 connected to the actuator 16, a plate 28 disposed within the framework 27 and connected to the vibrator 17 and mechanical or pneumatic springs 29, 30 disposed between opposite sides of the plate 28 and the upper and lower members of the framework 27.

1. A machine for testing materials, comprising a frame, upper and lower grips for holding a specimen to be tested, a load cell interposed between the upper grip and the frame, an actuator for applying cyclical loading to the lower grip, an electromagnetic vibrator connected to the lower grip and a spring unit interposed between the actuator and the vibrator.

2. A machine according to claim 1, wherein the actuator is capable of applying compression loads to the specimen and the spring unit is constituted by a gas filled bag interposed between a lower member attached to the actuator and an upper member attached to the vibrator and also capable of bearing against the undersurface of the lower member.

3. A machine according to claim 1, wherein the actuator is capable of applying tension loads to the specimen and the spring unit is constituted by a gas

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A machine for testing materials Atypical machine for testing materials is shown in Figure 1 of the accompanying drawings. It includes upper and lower grips 10,11 for holding the specimen 12 to be tested, the upper grip being connected through a load cell 13 to the top member 14 of the machine frame and the lower grip being connected to a hydraulic or electric actuator 16 fixed to the machine frame. In use of the machine the actuator 16 is caused by an electrical control system including a function generator to apply cyclic loading to the specimen, which may typically take the form A shown in Figure 2 which is a plot of load against time. A hydraulic actuator can only apply such cyclic loading A to the specimen at a relatively low frequency in the range, at most, of 100-200 Hz. It is sometimes required, however, to apply to the specimen not only such low frequency major cycle loads, but also minor cycle loads of much higher frequency unattainable hydraulically or electrically, such as are shown at B in Figure 2. A typical instance is the fatigue testing of gas turbine blades in which the amplitude of the major cycle loads may, for example, be of the order 5 tons and that of the minor cycle loads of the order of +1/2ton. The invention provides for this by providing between the actuator and the lower grip an electrodynamic vibrator with a spring unit interposed between the actuator and the vibrator. An electrodynamic vibrator is a well known piece of equipment and comprises a field coil surrounding a core of ferromagnetic material, a source of D.C. for energizing the field coil, a moving coil disposed in a gap between the field coil and the core, a table which extends upwardly from the moving coil and is guided to exclude torsional and transverse movement of the moving coil and permit vertical movement only of the moving coil and an amplifier for applying A.C. signals to the moving coil. In normal use a test object to be subjected to vibration is clamped to the table of the vibrator but when the vibrator is included in a materials testing machine in accordance with the invention the table is attached to the lower grip. The invention will now be further described with reference to the embodiments shown in Figures 3 to 6 of the accompanying drawings, in which: Figure 3 is a view similar to Figure 1 showing the known testing machine modified in accordance with the invention, and capable of applying compression loads to the specimen; Figure 4 is an enlarged view of a portion of the machine shown in Figure 3; Figure 5 is a view similar to Figure 4 showing a modification capable of applying tension loads to a specimen, and Figure 6 is a view again similar to Figure 4 and showing a further modification capable of applying both compression and tension loads to the specimen. Like reference numerals denote like parts throughout the Figures. In the embodiment of the invention shown in Figures 3 and 4 an electrodynamic vibrator 17 is interposed between the actuator 16 and the lower grip 11, the table 18 of the vibrator being connected to the lower end of the lower grip 11. As shown a pneumatic spring 19 is interposed between the actuator 16 and 17. This pneumatic spring consists of a rubber bag 20 filled with gas, preferably air, under pressure which is sandwiched between upper and lower metal plates 21,22 held within a generally C-shaped bracket 23 attached to the vibrator 17. The lower plate 22 is attached to the actuator 16.When the actuator 16 is not in operation the vibrator is relieved of load from the compressed gas in the bag 20 by the lower lips 24 of the bracket 23 but when the actuator 16 is in operation the plate 22 is lifted from these lips and the actuator 16 and the vibrator 17 can operate jointly on the specimen to subject it to major and minor load cycles of the kind shown in Figure 2. The apparatus shown in Figures 3 and 4 is suitable when the actuator 16 is intended to apply compression loads to the specimen. When it is desired to apply tension loads the apparatus is modified as shown in Figure 5, the rubber bag 20 and the plates 21,22 being disposed between a framework 25 connected to the actuator 16 and bearing through the plate 21 on the top of the bag and another framework 26 bearing through the plate 22 on the bottom of the bag and connected to the vibrator 17, the sides of the framework 25 extending through apertures in the base of the framework 26. Compression of the pneumatic spring 19 therefore applies a tension force to the specimen instead of a compression force as in Figure 3. Figure 6 shows a further modification capable of applying both compression and tension loads to the specimen and therefore operating through zero load. It includes a framework 27 connected to the actuator 16, a plate 28 disposed within the framework 27 and connected to the vibrator 17 and mechanical or pneumatic springs 29, 30 disposed between opposite sides of the plate 28 and the upper and lower members of the framework 27. CLAIMS

3. A machine according to claim 1, wherein the actuator is capable of applying tension loads to the specimen and the spring unit is constituted by a gas filled bag interposed between a framework attached to the actuator and bearing against the top of the bag and another framework attached to the vibrator and bearing against the bottom of the bag.

4. A machine according to claim 1, wherein the actuator is capable of applying both compression and tension loads to the specimen and the spring unit is constituted by a framework connected to the actuator, a plate disposed within the framework and connected to the vibrator and springs disposed between opposite sides of the plate and upper and lower members of the framework.