GB2379276A

GB2379276A - Impact testing apparatus

Info

Publication number: GB2379276A
Application number: GB0125616A
Authority: GB
Inventors: Nicholas Clive Osborne
Original assignee: PROCOM TECHNICAL SERVICES Ltd
Current assignee: PROCOM TECHNICAL SERVICES Ltd
Priority date: 2001-08-25
Filing date: 2001-10-24
Publication date: 2003-03-05
Anticipated expiration: 2021-10-24
Also published as: GB0120700D0; GB0125616D0; GB2379276B

Abstract

The impact material testing apparatus 10 includes an impact carriage 14 which is engaged with guide rails. The guide rails are parallel and spaced apart laterally and extend longitudinally along the apparatus. The apparatus 10 is horizontal and the impact carriage 14 is driven solely by a driving carriage 36 which is driven by a linear motor 38. In use, the impact carriage 14 is driven towards the specimen 11 by the driving carriage 36 pushing the impact carriage 14. Prior to impacting the specimen 11 the driving carriage 36 is rapidly decelerated to a stop and is then quickly reversed to a position which is not accessible to the impact carriage 14. This area is not accessible to the impact carriage 14 as a result of stops 35. Accordingly, if the impact carriage 14 rebounds from the specimen 11, the impact carriage 14 will not be able to reach the driving carriage 36 and therefore prevents damage to the driving means.

Description

IMPACT TESTING APPARATUS Field of the Invention The present invention relates to impact testing apparatus and to a method of impact testing materials.

Background to the Invention Tests and, especially impact tests, are conducted on materials in order to discover characteristics of the material. Such tests may be conducted on various materials, structures or sub-structures. Prior art apparatus includes vertical impact testing which comprises an apparatus consisting of a strong base on which is mounted a supporting tower. Attached to the tower are two or more vertical guide bars. A drop weight of fixed or variable mass is mounted between the guide bars the mass such that it is free to move in a vertical direction with low friction.

The specimen to be tested is mounted on a sample support provided in the base. A striker at the bottom of the drop weight is arranged to hit the sample. A winch system drives a catcher up and down the tower. The catcher is equipped with a mechanism to pick up the drop weight and release it.

For the purposes of the test, the sample is inserted on the support. The catcher attached to the drop weight, is winched up to a particular height. The height is chosen according to the required impact speed or velocity.

The catcher then releases the drop weight, which falls

under gravity down the tower until it impacts the sample. Following the impact, the winch lowers the catcher down on to the dropped weight, and the catcher picks up the weight which is returned to the release height ready for the next test.

A problem with vertical impact testing apparatus is that the impact speed is dependent on the height of the tower. High impact speeds require unfeasibly large apparatus, since the required height varies as the square of the velocity. A three metre tower is a practical limit for most locations, allowing impacts up to 7.6 metres per second. A speed of 18 metres per second (40 miles per hour) would require a tower 16.5 metres tall.

Similarly, low impact speeds are hard to achieve accurately, since they require a very low release height.

Practical minimum release height of 0.1 metres equates to an impact velocity of 1.4 metres per second. Anything less than this is very difficult to achieve with any accuracy.

Furthermore, in order to load the sample, a drop weight needs to be raised above the impact position. This has implications for operator safety.

In addition, when testing samples that are highly deformable, the total energy supplied by the drop weight is not well defined. This is because the energy depends on the total height through which the drop weight falls.

This is the distance between the drop weight and the sample at the release position, plus the additional height that the impact weight falls after it hits the sample.

This additional height is unlikely to be known in advance, since it is precisely one of the properties that the test is designed to measure. This lack of control over the impact energy can be a serious disadvantage in some circumstances.

Finally, for tests where the specimen is not penetrated by the striker, the drop weight will typically bounce off the specimen after the impact. In order to prevent the drop weight striking the specimen for a second time after it has rebounded, a fast acting mechanism needs to be incorporated in order to catch the drop weight. In existing systems, this mechanism only works when the height of the rebound exceeds a certain value. When a drop weight only bounces a short distance off a specimen, secondary impacts will occur.

It is an aim of the present invention to overcome at least one problem associated with prior art whether referred to herein or otherwise.

Summary of the Invention According to a first aspect of the present invention there is provided material impact testing apparatus comprising impact means for impacting the material, the apparatus further comprising driving means in order to drive the impact means towards the material wherein the driving means is arranged, in use, to drive the impact means towards the material and to release the impact means prior to the impact means impacting the material.

Preferably the driving means comprises a driving carriage.

Preferably the driving carriage is arranged, in use, to push the impact means towards the material. Preferably the driving carriage is arranged to be stopped prior to the impact means impacting the material and then reversed away from the impact means. Preferably the driving carriage is arranged to be stopped and reversed to a location which is not accessible to the impact means.

The apparatus may comprise guide means in order to guide the movement of the impact means. The guide means may be substantially horizontal. Preferably, the impact means is arranged, in use, to move along a substantially horizontal axis.

Preferably the impact means is solely driven by the driving means and is not accelerated by gravity.

Preferably the impact means comprises an impact carriage.

Preferably the impact means has a predetermined mass.

Preferably movement of the impact means is directed by guide means. The guide means may comprise guide rails and preferably comprises two guide rails. Preferably the impact means is mounted on the guide rails by bearings and preferably low friction bearings and more preferably low friction linear bearings. Preferably the guide rails are spaced laterally across the apparatus and the impact means

locates therebetween. Preferably the impact means is solely supported on the guide means.

Preferably the impact means comprises an impact member projecting outwardly from the impact carriage.

Preferably the movement of the driving carriage is directed by guide means. The guide means may comprise a guide rail and preferably comprises two guide rails.

Preferably the driving carriage is mounted on the guide rails by bearings and preferably low friction bearings and more preferably low friction linear bearings. Preferably the guide rails are spaced laterally across the apparatus and the driving carriage locates therebetween. Preferably the driving carriage is solely supported on the guide means.

Preferably the driving means comprises a motor and more preferably a linear motor.

The driving means may include coupling means in order to secure the driving means to the impact means. The coupling means may enable the driving means to pull the impact means. The coupling means may be selectively switched on or off in order to selectively couple the driving means to the impact means.

Preferably the apparatus comprises recording means.

The recording means may comprise a sensor located in the impact means. The sensor may comprise a force transducer.

The sensor may comprise an accelerometer.

Preferably the apparatus comprises recording means to record data relating to the impact. Preferably the recording means records data relating to the velocity of the impact means prior to impacting the material.

Preferably the recording means records data relating to the force between the impact means and the material during the impact. Preferably the recording means records data relating to the acceleration or deceleration of the impact means.

The recording means may comprise actuating means in order to start and stop the recording means. The actuating means may comprise a light beam and preferably comprises a laser light beam. The actuating means may comprise an interruption member. Preferably the interruption member is mounted on the impact means. The interruption means may be arranged, in use, to interrupt the light beam as the impact means moves towards the material. The actuating means may be arranged to signal the start of a recording period following an interruption of the light beam by the interruption member. Preferably the light beam is located near to material support means.

Preferably the apparatus comprises stopping means in order to restrict the movement of the impact means.

Preferably the apparatus comprises two stopping means to restrict movement of the impact means in a first direction and a second direction. The first stopping means and the second stopping means define a limited section in the apparatus between which the impact means can move.

The or each stopping means may comprise a shock absorber and preferably comprises a pair of shock

absorbers. Preferably the stopping means is arranged, in use, to enable the driving carriage to move therethrough.

Preferably the apparatus comprises control means in order to control the movement of the driving carriage. The control means may monitor the position and/or speed and/or acceleration of the driving carriage. The control means may comprise a linear encoder.

The longitudinal length of the or each guide rail may be less than 10m and preferably is less than 5m and more preferably is less than 2.5m.

The longitudinal length of the or each guide rail may be greater than 0. 5m and preferably is greater than 1m and more preferably is greater than 2m.

The lateral separation of the guide rails may be less than 1m and preferably is less than 0. 75m and more preferably is less than 0. 5m.

The lateral separation of the guide rails may be greater than 0. 05m and preferably is greater than O. lm and more preferably is greater than 0. 2m.

Preferably the apparatus comprises material support means in order to support the material and preferably a specimen of the material. Preferably the support means is located at the longitudinal end of the apparatus.

Preferably the support means is adjustable in order to support materials of differing dimensions.

According to a second aspect of the present invention there is provided a method of impact testing a material comprising moving impact means by driving means and releasing the impact means from the driving means prior to the impact means impacting material to be tested.

Preferably the method comprises pushing the impact means with a driving carriage. Preferably the method comprises stopping and reversing the driving carriage to a location at which stopping means for stopping movement of the impact means is located between the driving carriage and the impact means.

The method may comprise coupling the driving means to the impact means. The method may comprise pulling the impact means with the driving means to an initial starting position and preferably then releasing the coupling means.

The method may comprise recording the force between the impact means and the material during impact. The method may comprise recording the acceleration of the impact means.

Brief Description of the Drawings The present invention will now be described, by way of example only, with reference to the drawings that follow, in which: Figure 1 is a plan view of an embodiment of the present invention.

Figure 2 is a plan view of an embodiment of the present invention prior to impact testing.

Figure 3 is a plan view of an embodiment of the present invention during impact testing.

Figure 4 is s plan view of an embodiment of the present invention following impact testing.

Figure 5 is a plan view of an embodiment of the present invention following impact testing.

Description of Preferred Embodiment The impact material testing apparatus 10 comprises guide means in the form of horizontal guide rails 12, as shown in Figure 1. The apparatus further comprises impact means in the form of an impact carriage 14 which is engaged with guide means in the form of guide rails. The apparatus includes two guide rails which are parallel and spaced apart laterally and extend longitudinally along the apparatus 10. The impact carriage 14 is mounted on the two guide rails 12 and locates between the two guide rails.

The impact carriage 14 has movement means in the form of low friction linear bearings which support the carriage on the guide rail 12 and enable relative movement therebetween. The impact carriage 14 comprises a body having a predetermined mass in order to create a force on impact.

The apparatus 10 comprises an impact member 18 or striker which is located and mounted to the front of the impact carriage 14. The impact member 18 is arranged to impact a specimen 11 of a material in order for a characteristic of the material to be measured. The impact member has a sensor means or more specifically force measuring means, in the form of a force transducer 20, located therein. The force transducer 20 measures the force transferred or applied from the impact carriage to the specimen during a test. Alternatively, the impact member may comprise acceleration measuring means in the form of an accelerometer as the sensor means. The force transducer may perform better when the change in velocity during the impact is small (for example when the sample is penetrated) and an accelerometer may perform better when the change in velocity is large (for example when the impact means rebounds from the sample).

In use, the driving means is arranged to push the impact means. The driving means includes a switch 50 in order to signal when the driving means is in contact with the impact means.

The apparatus comprises force recording means comprising a transient recorder 21. The signal from the force transducer 20 or accelerometer passes through an amplifier 22 and then to the transient recorder 21. The output from the transient recorder 21 is communicated to a computer 24.

The apparatus further comprises control means to control the recording of the signal from the force transducer 20 or accelerometer by the recording means.

The control means informs the computer when the output from the transient recorder should be recorded and when the recording should cease. This recording period coincides with the impact period between the impact member 18 and the specimen 11.

The control means comprises a light beam and, preferably, a laser light beam emitted from a laser 26.

When the beam is uninterrupted the beam shines on a photoreceptor 28 mounted on an opposing lateral side of the apparatus. The control means further comprises actuating means to start and stop the recording of data. The actuating means comprises an interruption member 30 or flag mounted on the impact carriage 14. As the impact carriage moves towards the specimen, the interruption member 30 will obscure or interrupt the light beam for a period of time. Each time period is recorded by a timer 32 in order for the velocity of the impact carriage to be measured. Once the interruption member 30 no longer interrupts the beam then this signals for the commencement of the recording period for recording the force from the force transducer 20. The output of the transient recorder 22 and timer 32 are communicated to the computer 24 for analysis.

In use, if the impact member 18 penetrates the specimen, stop members or shock absorbers 34 prevent the further movement of the impact carriage 14.

Alternatively, if the specimen causes the impact carriage 14 to rebound, a second set of stop members or shock absorbers 35 are located at the opposite longitudinal end of the apparatus 10 in order to retain the impact carriage

14 in the apparatus 10 and to restrain the further movement of the impact carriage 14.

The apparatus 10 is horizontal and the impact carriage 14 is driven by driving means comprising a driving carriage 36 which preferably comprises an impeller. The driving carriage 36 is driven by a motor and preferably by a linear motor 38. The driving carriage 36 comprises position indicating means in order to provide feedback on the position of the driving carriage along the guide rails 12. The position indicating means comprises a linear encoder 54. The driving carriage 36 has movement means in the form of low friction linear bearings 40 which support the carriage 36 on the guide rails 12 and enable relative movement therebetween. The driving carriage 36 is connected to driving control means in order to precisely control the speed and acceleration of the driving carriage 36. The linear encoder 54 provides feedback on the position of the driving carriage 36 to the driving control means. The driving control means comprises a computer which may use a software program to control the position, speed and acceleration of a driving carriage 36.

The driving carriage 36 has indicating means in order to indicate when the driving carriage 36 is in physical contact with the impact carriage 14. The indicator means may comprise a switch mounted on the front of the driving carriage 36 which senses the contact of the impact carriage 14.

As shown in Figure 2, prior to the impact test, the specimen 11 of material is located in place in specimen support means 60. The impact carriage is located near the

second set of shock absorbers 34 and just in front of the shock absorbers 34. The driving carriage 36 is in contact with the impact carriage 14.

The impact carriage 14 is then driven towards the specimen 11 under control of the computer by the linear motor. The linear motor is controlled to provide a substantially constant acceleration of the driving carriage 36 and hence the impact carriage 14. The acceleration is calculated to produce an impact velocity for the impact carriage 14 at a position where the impact carriage 14 is located near the specimen 11, such a position is shown in Figure 3.

At this position, the driving carriage 36 is rapidly decelerated to a stop and is then quickly reversed so as to travel towards its initial position. Since the driving carriage 36 was not physically linked or joined to the impact carriage 14, the impact carriage 14 will continue its movement towards the specimen 11. There is no significant friction caused by the release of the impact carriage 14 and the driving carriage 36. In addition, the impact carriage 14 and, more specifically, the impact member 18 only has a relatively short distance to travel prior to impacting the specimen 11. Accordingly, the impact carriage 14 will substantially continue at the constant velocity achieved prior to the driving carriage 36 releasing the impact carriage 14.

Prior to the impact the interruption member 30 interrupts the light beam and the timer starts recording.

When the interruption member 30 no longer interrupts the light beam, the timer stops recording and output from the

transient recorder 22 starts recording the signal from the force transducer.

There are two possible outcomes of the impact. The first comprises the impact carriage 14 rebounding as a result of the impact between the impact member 18 and the specimen 11. This results in the impact carriage 14 travelling back towards the starting position. The driving carriage 36 was reversed rapidly prior to the impact and is arranged to locate at a position past the second set of shock absorbers 35. Accordingly, the rebound of the impact carriage 14 towards its starting position will be prevented and restrained by the second set of shock absorbers 35. This, thereby, prevents an impact between the impact carriage 14 and the driving carriage 36 and prevents any damage therebetween. The release distance at which the driving carriage 36 releases the impact carriage 14 is selected so as to ensure that the impact carriage 14 would not strike the driving carriage 36 following a rebound and ensures sufficient time for the driving carriage 36 to be located behind the second set of shock absorbers 35. Therefore, the release distance is calculated to take into account the release velocity of the impact carriage 14 as well as the time taken for the driving carriage 36 to move to a safe position.

In the second situation, the impact member 20 may penetrate the specimen 11 and, therefore, the impact carriage 14 will continue its movement along the guide rails 12, albeit at a reduced velocity. The impact carriage 14 will then abut the first set of shock absorbers 34 in order to prevent any further movement of

the impact carriage 14 and also prevent any damage to the impact carriage 14 or the apparatus 10.

In both cases, following the test, the linear motor 38 then drives the driving carriage 36 forward along the guide rails 12 in order to abut the impact carriage 14.

The switch 50 located on the driving carriage 36 signals when the two carriages 14,36 are just touching and a coupling 52 is activated in order for the driving carriage 36 to move or pull the impact carriage 14 back to an initial starting position ready for another test. At this position, the coupling is then released.

The force or acceleration measured by the transient recorder 20 and the reading from the timer 32 are transferred to the computer 24.

The computer 24 calculates the impact velocity by dividing the dimension of the interruption member 30 or flag by the time recorded by the timer 32.

The acceleration (or deceleration) of the impact carriage 14 can be directly measured or determined by dividing the force measurement by the mass of the impact carriage 14. The velocity of the impact carriage 14 throughout the impact can be calculated by integrating the acceleration value with respect to time, taking into account the initial impact velocity. The position of the impact carriage 14, and hence the deflection of the test specimen 11 throughout the impact can be calculated by integrating the velocity values with respect to time.

Further features can be extracted, from the force, acceleration, velocity, deflection and time data as required.

The apparatus 10 has several advantages which include the use of a linear motor 38 rather than a belt drive which would result in a moving part having lower inertia and hence higher acceleration. This allows high velocity testing formed on a compact apparatus.

The use of a linear motor 38 and linear encoder 54 gives very accurate closed loop control over a wide range of impact velocities. This provides a precisely defined impact energy, and therefore tighter control over test conditions and very high reproducibility. The apparatus 10 only has two moving parts (the driving carriage 36 and impact carriage 14) which should mean high reliability.

With no stored energy, and a minimum of moving parts, the apparatus 10 is safer than prior art apparatus. The shock absorbers 34,35 at both ends, and the ability to park the driving carriage, both the rebound and penetration tests may be performed in the apparatus 10.

An interchangeable sample support 60 area allows for testing specimens of different geometries, and very large specimens increasing the versatility of the apparatus 10.

In addition, since it is performed on the horizontal this means that low impact velocities may be easily achieved.

Finally, horizontal impact means that the impact energy is fixed even for specimens that undergo large deformation.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to

this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s). The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS 1. Material impact testing apparatus comprising impact means for impacting the material, the apparatus further comprising driving means in order to drive the impact means towards the material wherein the driving means is arranged, in use, to drive the impact means towards the material and to release the impact means prior to the impact means impacting the material.
2. Apparatus according to claim 1 in which the driving means comprises a driving carriage.
3. Apparatus according to claim 2 in which the driving carriage is arranged, in use, to push the impact means towards the material.
4. Apparatus according to claim 2 or claim 3 in which the driving carriage is arranged to be stopped prior to the impact means impacting the material and then reversed away from the impact means.
5. Apparatus according to claim 4 in which the driving carriage is arranged to be stopped and reversed to a location which is not accessible to the impact means.
6. Apparatus according to any preceding claim in which the apparatus comprises guide means in order to guide the movement of the impact means.
7. Apparatus according to claim 6 in which the guide means is substantially horizontal.

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8. Apparatus according to any preceding claim in which the impact means is arranged, in use, to move along a substantially horizontal axis.
9. Apparatus according to any preceding claim in which the impact means is solely driven by the driving means and is not accelerated by gravity.
10. Apparatus according to any preceding claim which movement of the impact means is directed by guide means.
11. Apparatus according to claim 10 in which the impact means is solely supported on the guide means.
12. Apparatus according to any preceding claim in which the impact means comprises an impact member projecting outwardly from an impact carriage.
13. Apparatus according to claim 2 or any one of claims 3 to 12 when dependent upon claim 2, in which the movement of the driving carriage is directed by guide means.
14. Apparatus according to claim 13 in which the driving means is solely supported on the guide means.
15. Apparatus according to any preceding claim in which the driving means comprises a linear motor.
16. Apparatus according to any preceding claim in which the driving means includes coupling means in order to secure the driving means to the impact means.

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17. Apparatus according to claim 16 in which the coupling means enables the driving means to pull the impact means.
18. Apparatus according to any preceding claim in which the apparatus comprises recording means.
19. Apparatus according to claim 18 in which the recording means comprises a sensor located in the impact means.
20. Apparatus according to claim 19 in which the sensor comprises a force transducer.
21. Apparatus according to claim 19 in which the sensor comprises an accelerometer.
22. Apparatus according to any preceding claim in which the apparatus comprises stopping means in order to restrict the movement of the impact means.
23. Apparatus according to any preceding claim in which the apparatus comprises two stopping means to restrict movement of the impact means in a first direction and a second direction.
24. Apparatus according to claim 23 in which the first stopping means and the second stopping means define a limited section in the apparatus between which the impact means can move.
25. Apparatus according to any one of claims 22 to 24 when dependent upon claim 2 in which the stopping means is arranged, in use, to enable the driving carriage means to move therethrough.

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26. Apparatus according to claim 2 or any one of claims 3 to 25 when dependent upon claim 2, in which the apparatus comprises control means in order to control the movement of the driving carriage.
27. Apparatus according to claim 26 in which the control means comprises a linear encoder.
28. A method of impact testing a material comprising moving impact means by driving means and releasing the impact means from the driving means prior to the impact means impacting material to be tested.
29. A method according to claim 28 comprising pushing the impact means with a driving carriage.
30. A method according to claim 29 comprising stopping and reversing the driving carriage to a location at which stopping means for stopping movement of the impact means is located between the driving carriage and the impact means.
31. A method according to any one of claim 28 to claim 30 comprising coupling the drive means to the impact means.
32. A method according to any one of claim 31 comprising puling the impact means with the driving means to an initial starting position.
33. A method according to claim 31 or claim 32 comprising releasing the coupling means.

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34. A method according to any one of claim 28 to claim 33 comprising recording the force between the impact means and the material during impact.

35. A method according to any one of claim 28 to claim 34 comprising recording the acceleration of the impact means.
35. Material impact testing apparatus substantially as herein described with reference to, and shown in, any of the accompanying drawings.
36. A method of impact testing a material substantially as herein described, with reference to, and shown in, any of the accompanying drawings.