Hopkinson device strain test signal correction system and working method thereof

Abstract

The invention provides a Hopkinson device strain test signal correction system and a working method thereof. The Hopkinson device strain test signal correction system comprises a sample connecting device, a Hopkinson device, a laser interference velocity measurement system and a processor, the sample connecting device is used for fixing a to-be-tested sample and is respectively connected with the Hopkinson incident bar and the transmission bar to load elastic waves on the to-be-tested sample; the Hopkinson device is used for generating high-strain-rate impact on a to-be-tested sample through the incident bar and the transmission bar; the laser interference velocity measurement system is used for collecting velocity signals at a first interface and a second interface of a to-be-tested sample in real time to obtain a first velocity and a second velocity; and the processor is used for obtaining the corrected strain, stress and strain rate of the to-be-tested sample based on the obtained first speed and second speed.

Description

Technical Field

[0001] The invention belongs to the technical field of Hopkinson bar testing, and in particular relates to a Hopkinson device strain test signal correction system and a working method thereof. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In the field of material mechanics research, the Hopkinson device is a widely recognized and used general test device for material dynamics. The device was originally used for high strain rate compression tests and collects signals through equipment such as strain gauges and dynamic strain gauges.

[0004] With the development of the Hopkinson device test technology, the initial high strain rate compression test has been expanded to high strain rate tensile test, shear test, dynamic fracture toughness test, etc. People have made various modifications to the Hopkinson device according to the test requirements, mainly using more and more sample connection devices to connect various types of test samples, such as tensile sample connection devices, superhard material sample connection devices, etc.

[0005] The inventors found that, at present, in the high strain rate mechanical test of the Hopkinson device using the sample connection device, the signal measurement method still uses the traditional substitution test, that is, a strain gauge is attached to the surface of the Hopkinson bar at a certain length away from the sample interface to measure the strain signal, and this signal replaces the strain signal at the interface of the tested sample. Studies have shown that this substitution method has many problems. Due to the use of the sample connection device, the original test conditions are broken, and the elastic wave is distorted when passing through the sample connection device. Continuing to use the original substitution method for test calculations will produce errors that cannot be ignored. Summary of the invention

[0006] The embodiment of the present invention provides a Hopkinson device strain test signal correction system and a working method thereof, so as to solve the problem in the prior art that in the high strain rate mechanical test of the Hopkinson device using a sample connection device, the signal measurement method still uses the traditional substitution method for test calculation, resulting in non-negligible errors.

[0007] According to a first aspect of an embodiment of the present invention, there is provided a Hopkinson device strain test signal correction system, comprising a sample connection device, a Hopkinson device, a laser interferometer speed measurement system, and a processor;

[0008] The sample connection device is used to fix the sample to be tested, and is connected to the Hopkinson incident rod and the transmission rod respectively to achieve elastic wave loading on the sample to be tested;

[0009] The Hopkinson device is used to generate a high strain rate impact on the test sample through the incident rod and the transmission rod;

[0010] The laser interferometer speed measurement system is used to collect speed signals at the first interface and the second interface of the test sample in real time to obtain the first speed and the second speed;

[0011] The processor is used for obtaining the corrected strain, stress and strain rate of the sample to be tested based on the obtained first speed and second speed.

[0012] Furthermore, the high strain rate impact includes high strain rate compression and high strain rate tension, and the high strain rate compression and high strain rate tension use different connection devices.

[0013] Furthermore, when the high strain rate impact is a high strain rate compression, the connecting device includes a first sleeve and a second sleeve located on both sides of the sample to be tested, and a pad is embedded in the first sleeve and the second sleeve. One end of the pad is connected to the incident rod or the transmission rod of the Hopkinson device, and the other end is connected to the sample to be tested.

[0014] Furthermore, the first sleeve and the second sleeve include a pressure rod connecting sleeve, a pad connecting sleeve and a flange located at one end of the pad connecting sleeve that are fixedly connected in sequence, the pad is embedded in the pad connecting sleeve, the incident rod or the transmission rod passes through the pressure rod connecting sleeve and is connected to the pad, and is spaced a preset distance from the pad connecting sleeve.

[0015] Furthermore, when the high strain rate impact is a high strain rate compression, the laser probe in the laser interferometer velocity measurement system is arranged at the end surface of the flange, and the laser probe is spaced a preset distance from the flange.

[0016] Furthermore, when the high strain rate impact is high strain rate stretching, the connecting device includes a first clamping module and a second clamping module located on both sides of the sample to be tested, and one end of the first clamping module and the second clamping module are provided with bolts for connecting to the incident rod or the projection rod, and the other end is used to clamp the clamping end of the sample to be tested.

[0017] Furthermore, when the high strain rate impact is high strain rate stretching, the laser probe in the laser interferometer speed measurement system is arranged at the end surface position of the lower clamping plate of the clamping module, and the laser probe is spaced a preset distance from the lower clamping plate.

[0018] Furthermore, based on the obtained first speed and second speed, the corrected strain, stress and strain rate of the sample to be tested are obtained, which is specifically expressed as follows:

[0019]

[0020] Where V1(t) is the velocity at the first interface, V2(t) is the velocity at the second interface, ε t is the strain at the X2 interface; C b 、E b , A b are the elastic wave velocity, elastic modulus and cross-sectional area of ​​the Hopkinson bar respectively; ε s , σ s , L s , A s They are the strain of the specimen, the stress of the specimen, the strain rate of the specimen, the gauge length of the specimen and the cross-sectional area.

[0021] Furthermore, the laser beam emitted by the laser probe of the laser interference velocity measurement system is parallel to the axis of the Hopkinson bar, and the laser beam is vertically incident on the first interface and the second interface of the tested sample.

[0022] According to a second aspect of an embodiment of the present invention, a working method of a Hopkinson device strain test signal correction system is provided, comprising:

[0023] Clamp the sample to be tested through the sample connecting device;

[0024] Connect the sample connection device to the incident rod and the transmission rod of the Hopkinson device respectively;

[0025] Starting the Hopkinson device to perform high strain rate impact, and performing high strain rate impact loading on the test sample through the sample connection device;

[0026] The laser interference speed measurement system is used to collect speed signals at the first interface and the second interface of the test sample in real time to obtain the first speed and the second speed;

[0027] Based on the obtained first speed and second speed, the corrected strain, stress and strain rate of the test sample are obtained.

[0028] One or more of the above technical solutions have the following beneficial effects:

[0029] (1) The present invention provides a Hopkinson device strain test signal correction system and a working method thereof. The scheme innovatively proposes to use a laser interferometer speed measurement system to directly test the speed signals between the sample and the X1 interface and the X2 interface, thereby avoiding the test errors introduced by the traditional replacement test method. Through the obtained test signal, the strain rate, strain, stress and other parameters of the sample can be accurately calculated, thereby correcting the interference of the sample connection device on the strain test signal and ensuring the accuracy and reliability of the test data.

[0030] (2) The solution described in the present invention can effectively meet the needs of various samples in compression tests and tensile tests through the independently designed sample connection device. For example, compression samples such as ceramics, glass, spinel, and high-hardness alloys will break during high strain rate tests, which will cause serious damage to the end faces of the incident rod and the transmission rod. The compression sample connection device designed by the present invention can effectively protect the end faces of the incident rod and the transmission rod from being damaged, and effectively realize high strain rate compression loading; such as high strain rate tensile tests on materials such as plastics, fiber-reinforced composites, and metals, the tensile sample connection device designed by the present invention can firmly connect the tensile sample and can realize rapid replacement of the tensile sample, thereby improving the test efficiency.

[0031] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0033] Figure 1 The present invention is a schematic diagram of the principle of a Hopkinson device strain test signal correction system for performing high strain rate compression test test signal correction.

[0034] Figure 2 It is a left side view of the sleeve component described in the embodiment of the present invention.

[0035] Figure 3 The present invention is a schematic diagram of the principle of a Hopkinson device strain test signal correction system for performing high strain rate tensile test test signal correction.

[0036] Figure 4 It is a front view of the clamping plate component described in the embodiment of the present invention.

[0037] Figure 5 It is a comparison diagram of the stress-strain curve of the superhard material sample obtained by the modified strain signal described in the embodiment of the present invention and the traditional replacement method.

[0038] Figure 6 A comparison diagram of the stress-strain curve of a tensile specimen obtained by a modified strain signal described in an embodiment of the present invention and a conventional replacement method;

[0039] Among them, 1 is the incident pressure rod, 2 is the sleeve, 201 is the flange, 202 is the pressure rod connecting sleeve, 203 is the pad connecting sleeve, 3 is the pad, 4 is the superhard material sample, 5 is the laser probe at the X1 interface, 6 is the laser probe at the X2 interface, 7 is the laser interferometry speed measurement system, 8 is the transmission pressure rod, 9 is the incident pull rod, 10 is the splint, 101 is the upper splint, 102 is the lower splint, 11 is the splint connecting bolt, 12 is the tensile specimen, 13 is the laser probe at the X1 interface, 14 is the laser probe at the X2 interface, 15 is the laser interferometry speed measurement system, 16 is the transmission pull rod, 17 is the incident pull rod connecting bolt, and 18 is the transmission pull rod connecting bolt. DETAILED DESCRIPTION

[0040] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0041] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0042] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0043] In order to solve the problems existing in the prior art, the present embodiment provides a Hopkinson device strain test signal correction system, including a sample connection device, a Hopkinson device, a laser interferometer speed measurement system and a processor;

[0044] The sample connection device is used to fix the sample to be tested, and is connected to the Hopkinson incident rod and the transmission rod respectively to achieve elastic wave loading on the sample to be tested;

[0045] The Hopkinson device is used to generate a high strain rate impact on the test sample through the incident rod and the transmission rod;

[0046] The laser interferometer speed measurement system is used to collect speed signals at the first interface and the second interface of the test sample in real time to obtain the first speed and the second speed;

[0047] The processor is used for obtaining the corrected strain, stress and strain rate of the sample to be tested based on the obtained first speed and second speed.

[0048] In a specific implementation, the laser beam emitted by the laser probe of the laser interference velocity measurement system is parallel to the axis of the Hopkinson bar, and the laser beam is vertically incident on the first interface and the second interface of the tested sample.

[0049] In a specific implementation, the high strain rate impact includes high strain rate compression and high strain rate tension, and the high strain rate compression and high strain rate tension use different connection devices.

[0050] In a specific implementation, when the high strain rate impact is a high strain rate compression, the connecting device includes a first sleeve and a second sleeve located on both sides of the sample to be tested, and a pad is embedded in the first sleeve and the second sleeve. One end of the pad is connected to the incident rod or the transmission rod of the Hopkinson device, and the other end is connected to the sample to be tested.

[0051] Among them, the first sleeve and the second sleeve include a pressure rod connecting sleeve, a cushion block connecting sleeve and a flange located at one end of the cushion block connecting sleeve which are fixedly connected in sequence, the cushion block is embedded in the cushion block connecting sleeve, the incident rod or the transmission rod passes through the pressure rod connecting sleeve and is connected to the cushion block, and is spaced a preset distance from the cushion block connecting sleeve.

[0052] Specifically, Figure 1 and Figure 2 As shown, the sample connection device includes a sleeve 2 and a cushion block 3, which are coaxial and fixedly connected. The inner diameter of the pressure rod connecting sleeve 202 matches the outer diameter of the incident pressure rod 1 and the transmission pressure rod 8 and is slidably connected. The sleeve 2 has a flange 201 on one side close to the superhard material sample 4, which facilitates the laser probe to receive the laser signal reflected back by the flange 201.

[0053] like Figure 1 As shown, the laser probe is disposed at 2 mm to 8 mm, preferably 5 mm, of the end surface of the flange 201 to ensure that the laser probe does not contact the flange 201 before the elastic wave is transmitted to the first and second interfaces, thereby obtaining effective test data.

[0054] like Figure 2 As shown, in the axial direction, the length of the cushion block connecting sleeve 203 should be less than the length of the cushion block 3, and the cushion block connecting sleeve 203 does not contact the pressure rod on the side close to the pressure rod, and a gap of 1mm to 3mm is left, preferably 2mm.

[0055] The sleeve 2 is preferably made of steel, and the pad 3 is preferably made of tungsten carbide. The diameter of the pad 3 should be larger than the diameter of the superhard material sample 4. The gap between the flange 201 and the incident interface laser probe 5 is 2 mm to 8 mm, preferably 5 mm. The gap between the flange 201 and the transmission interface laser probe 6 is 2 mm to 8 mm, preferably 5 mm.

[0056] The laser interferometer speed measurement system 7 is a prior art and will not be described in detail here. It can be implemented by using a laser interferometer speed meter, which directly measures the instantaneous speed signal of the free end surface. Preferably, the diameter of the laser beam is 2 mm.

[0057] Grease is applied to the two end surfaces of the superhard material sample 4 that are in contact with the cushion block 3, and the incident pressure rod 1 and the transmission pressure rod 8 are pushed toward the direction of the superhard material sample 4 to squeeze and fix the superhard material sample 4.

[0058] For high strain rate compression tests, the following procedures are performed:

[0059] The Hopkinson device is started to perform a high strain rate compression test on the superhard material sample, generating a compressive elastic wave that loads the sample. The elastic wave propagates along the Hopkinson rod to the sample connecting device, and the superhard material sample is subjected to high strain rate impact compression loading through the sample connecting device. The velocity signal V1(t) at the X1 interface of the test sample and the velocity signal V2(t) at the X2 interface are collected by the laser interferometer velocimetry system.

[0060] By utilizing the collected velocity V1(t) curves at the X1 interface and the velocity V2(t) curves at the X2 interface of the tested superhard material sample, the incident strain and the transmitted strain are converted according to the one-dimensional stress wave theory, and then the strain rate, compressive stress and strain of the superhard material sample are obtained. The specific calculation formula is as follows.

[0061]

[0062] Among them, ε t is the strain at the X2 interface; C b 、E b , A b are the elastic wave velocity, elastic modulus and cross-sectional area of ​​the Hopkinson bar respectively; ε s , σ s , L s , A s They are respectively the strain of the superhard material specimen, the compressive stress of the specimen, the strain rate of the specimen, the gauge length and the cross-sectional area of ​​the specimen.

[0063] In a specific implementation, when the high strain rate impact is a high strain rate stretching, the connecting device includes a first clamping module and a second clamping module located on both sides of the sample to be tested, and one end of the first clamping module and the second clamping module are provided with bolts for connecting to the incident rod or the projection rod, and the other end is used to clamp the clamping end of the sample to be tested.

[0064] Specifically, Figure 3 and Figure 4As shown, the sample connection device includes a clamping plate 10, a clamping plate connecting bolt 11, an incident tie rod connecting bolt 17 and a transmission tie rod connecting bolt 18. The clamping plate 10 includes an upper clamping plate 101 and a lower clamping plate 102, and the inner sides of the upper clamping plate 101 and the lower clamping plate 102 are processed with serrations to firmly fix the clamping end of the tensile sample 12. One side of the lower clamping plate 102 is fixedly connected to the incident tie rod connecting bolt 17 and the transmission tie rod connecting bolt 18.

[0065] The lower clamping plate 102 is fixedly connected to the incident rod 9 and the transmission rod 16 through the incident rod connecting bolts 17 and the transmission rod connecting bolts 18 respectively. The clamping end of the tensile specimen 12 is placed between the upper clamping plate 101 and the lower clamping plate 102, and the three are clamped and fixedly connected through the clamping plate connecting bolts 11. Figure 3 As shown, the laser probes are placed at the X1 interface (i.e., the first interface) and the X2 interface (i.e., the second interface) of the gauge section of the tensile specimen respectively. The laser interferometer velocity measurement system emits a laser beam parallel to the axis of the Hopkinson bar through the laser probe, and the laser beam is vertically incident on the X1 interface and the X2 interface of the tested sample.

[0066] Specifically, the tensile specimen is divided into two clamping ends at both ends and a gauge section in the middle. This type of tensile specimen is the most common type in mechanical testing. In this embodiment, the upper clamping plate 101 and the lower clamping plate 102 fix the clamping ends, and the two sides of the gauge section (i.e., the first and second interfaces) coincide with the end surface of the lower clamping plate 102. Figure 3 The laser probe is placed 2mm to 8mm from the end surface of the lower clamping plate 102, preferably 5mm, to ensure that the laser probe does not contact the lower clamping plate 102 before the elastic wave is transmitted to the first and second interfaces, thereby obtaining effective test data.

[0067] Preferably, the incident rod 9, the tensile specimen connecting device 10, the clamping plate connecting bolt 11, and the transmission rod 16 are made of the same material, and in this embodiment, they are all made of high-strength steel.

[0068] For high strain rate tensile testing, the following process is performed:

[0069] The Hopkinson device is started to perform a high strain rate tensile test on the tensile specimen, generating a tensile elastic wave to load the specimen. The elastic wave propagates along the Hopkinson rod to the tensile specimen connecting device, and a high strain rate impact tensile loading is performed on the test specimen through the tensile specimen connecting device. The velocity signal V1(t) at the X1 interface of the tensile specimen and the velocity signal V2(t) at the X2 interface are collected by the laser interferometer velocimetry system.

[0070] By using the collected X1 interface velocity V1(t) and X2 interface velocity V2(t) curves of the tested tensile specimen, they are converted into incident strain and transmission strain according to the one-dimensional stress wave theory, and then the strain rate, tensile stress and strain of the tensile specimen are obtained. The calculation formula is consistent with that of the compression test, so it will not be repeated here.

[0071] In order to prove the effectiveness of the solution described in this embodiment, this embodiment has been verified by relevant experiments, specifically, Figure 5 As shown in FIG. 1 , it is a comparison diagram of the stress-strain curve of the superhard material sample obtained by the strain signal corrected by the scheme described in this embodiment and the traditional replacement method. Figure 6 As shown, it is a comparison diagram of the stress-strain curve of the tensile specimen obtained by the strain signal corrected by the scheme described in this embodiment and the traditional replacement method. Figure 5 and Figure 6 The effectiveness of the solution described in this embodiment can be intuitively obtained.

[0072] In one or more embodiments, a working method of a Hopkinson device strain test signal correction system is provided, comprising:

[0073] Clamp the sample to be tested through the sample connecting device;

[0074] Connect the sample connection device to the incident rod and the transmission rod of the Hopkinson device respectively;

[0075] Starting the Hopkinson device to perform high strain rate impact, and performing high strain rate impact loading on the test sample through the sample connection device;

[0076] The laser interference speed measurement system is used to collect speed signals at the first interface and the second interface of the test sample in real time to obtain the first speed and the second speed;

[0077] Based on the obtained first speed and second speed, the corrected strain, stress and strain rate of the test sample are obtained.

[0078] Those skilled in the art will appreciate that the units, i.e., algorithm steps, of the various examples described in the present embodiment can be implemented in electronic hardware or in a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A Hopkinson device strain test signal correction system, characterized in that: It includes a sample connection device, a Hopkinson device, a laser interferometer speed measurement system and a processor; The sample connection device is used to fix the sample to be tested, and is connected to the Hopkinson incident rod and the transmission rod respectively to achieve elastic wave loading on the sample to be tested; The Hopkinson device is used to generate a high strain rate impact on the test sample through the incident rod and the transmission rod; The laser interferometer speed measurement system is used to collect speed signals at the first interface and the second interface of the test sample in real time to obtain the first speed and the second speed; The processor is used for obtaining the corrected strain, stress and strain rate of the sample to be tested based on the obtained first speed and second speed.

2. A Hopkinson device strain test signal correction system as claimed in claim 1, characterized in that: The high strain rate impact includes high strain rate compression and high strain rate tension, and the high strain rate compression and high strain rate tension adopt different connection devices.

3. A Hopkinson device strain test signal correction system as claimed in claim 1, characterized in that: When the high strain rate impact is high strain rate compression, the connecting device includes a first sleeve and a second sleeve located on both sides of the sample to be tested, and a pad is embedded in the first sleeve and the second sleeve. One end of the pad is connected to the incident rod or the transmission rod of the Hopkinson device, and the other end is connected to the sample to be tested.

4. A Hopkinson device strain test signal correction system as claimed in claim 3, characterized in that: The first sleeve and the second sleeve include a pressure rod connecting sleeve, a cushion block connecting sleeve and a flange located at one end of the cushion block connecting sleeve which are fixedly connected in sequence. The cushion block is embedded in the cushion block connecting sleeve. The incident rod or the transmission rod passes through the pressure rod connecting sleeve and is connected to the cushion block, and is spaced a preset distance from the cushion block connecting sleeve.

5. A Hopkinson device strain test signal correction system as claimed in claim 3, characterized in that: When the high strain rate impact is high strain rate compression, the laser probe in the laser interference velocity measurement system is arranged at the end surface of the flange, and the laser probe is spaced a preset distance from the flange.

6. A Hopkinson device strain test signal correction system as claimed in claim 1, characterized in that: When the high strain rate impact is high strain rate stretching, the connecting device includes a first clamping module and a second clamping module located on both sides of the sample to be tested, and one end of the first clamping module and the second clamping module is provided with a bolt for connecting to the incident rod or the projection rod, and the other end is used to clamp the clamping end of the sample to be tested.

7. A Hopkinson device strain test signal correction system as claimed in claim 6, characterized in that: When the high strain rate impact is high strain rate stretching, the laser probe in the laser interference speed measurement system is arranged at the end surface position of the lower clamping plate of the clamping module, and the laser probe is spaced a preset distance from the lower clamping plate.

8. The Hopkinson device strain test signal correction system according to claim 1, characterized in that: Based on the obtained first speed and second speed, the corrected strain, stress and strain rate of the test sample are obtained, which is specifically expressed as follows: Where V1(t) is the velocity at the first interface, V2(t) is the velocity at the second interface, ε t is the strain at the X2 interface; C b 、E b , A b are the elastic wave velocity, elastic modulus and cross-sectional area of ​​the Hopkinson bar respectively; ε s , σ s , L s , A s They are the strain of the specimen, the stress of the specimen, the strain rate of the specimen, the gauge length of the specimen and the cross-sectional area.

9. A Hopkinson device strain test signal correction system as claimed in claim 1, characterized in that: The laser light beam emitted by the laser probe of the laser interference speed measurement system is parallel to the axis of the Hopkinson bar, and the laser light beam is vertically incident on the first interface and the second interface of the tested sample.

10. A working method of a Hopkinson device strain test signal correction system, characterized in that: include: Clamp the sample to be tested through the sample connecting device; Connect the sample connection device to the incident rod and the transmission rod of the Hopkinson device respectively; Starting the Hopkinson device to perform high strain rate impact, and performing high strain rate impact loading on the test sample through the sample connection device; The laser interference speed measurement system is used to collect speed signals at the first interface and the second interface of the test sample in real time to obtain the first speed and the second speed; Based on the obtained first speed and second speed, the corrected strain, stress and strain rate of the test sample are obtained.

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