A method for fatigue testing of plate-shaped materials

Abstract

The present invention relates to the technical field of fatigue performance testing of industrial products, and discloses a method for fatigue testing of plate-shaped materials, comprising the following steps: Step 1: fixing a test sample on an anti-buckling device, the anti-buckling device comprising two anti-buckling members and four sets of fasteners, each anti-buckling member having an I-shaped lubricating member positioning groove, a lubricating member being provided in the lubricating member positioning groove, and the shape of the lubricating member matching the shape of the lubricating member positioning groove, the test sample being clamped parallely between the two lubricating members and fixed by fasteners; Step 2: using a fatigue testing machine to perform S min <0 axial stress, ε min The technical solution of the present invention can use multiple control modes to perform axial fatigue tests on test samples under stress and strain control, and at the same time, can reduce test errors and improve test accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of fatigue performance testing of materials and industrial products, and in particular to a method for fatigue testing of plate-shaped materials. Background Art

[0002] Fatigue failure occurs when a material is subjected to repeated cycles of alternating loads, even when the stress level is far below the material's ultimate strength or even its yield point. When designing components and engineering structures, the timeframe for fatigue failure must be considered to avoid unnecessary property damage and personal injury.

[0003] Existing fatigue testing methods for plate materials usually use a unidirectional extensometer method to perform axial tension and compression bidirectional strain-controlled fatigue tests on test samples. Specifically, the test sample is fixed on an anti-buckling device, which includes two anti-buckling parts and four sets of fasteners. Each anti-buckling part has a strip-shaped lubricating part positioning groove, in which a lubricating part is provided. An extensometer positioning groove is provided on the side of the anti-buckling part away from the lubricating part positioning groove. The test sample is clamped in parallel between the two anti-buckling parts, and a unidirectional extensometer is fixed to one side of the test sample. A strain-controlled axial tension and compression fatigue test is performed on the test sample using a fatigue testing machine.

[0004] The disadvantages of this technical solution are: 1. When the test sample is subjected to strain-controlled axial tension and compression fatigue testing, the test sample is subjected to uneven force, the test error is large, and the measurement results are inaccurate; 2. Since this technical solution adopts a unidirectional extensometer test method, the extensometer is fixed on one side of the test sample during the test. During the test, the test sample will move laterally to one side of the extensometer, resulting in a large test error. Summary of the Invention

[0005] The present invention aims to provide a method for fatigue testing of plate-shaped materials, which can ensure that the stress on a test sample is uniform.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for fatigue testing of plate-shaped materials, comprising the following steps:

[0007] Step 1: Fix the test sample on the anti-buckling device, which includes two anti-buckling parts and four sets of fasteners. Each anti-buckling part has an I-shaped lubricating part positioning groove. A lubricating part is installed in the lubricating part positioning groove, and the shape of the lubricating part matches the shape of the lubricating part positioning groove. The test sample is clamped parallel to the two lubricating parts and fixed with fasteners.

[0008] Step 2: Use fatigue testing machine to test the sample min <0 axial stress, ε min<0 axial strain controlled fatigue test.

[0009] The beneficial effects of this solution are: min <0 axial stress, ε min When the axial strain is less than 0 and the fatigue test is controlled, the lubricating part is first fixed in the lubricating part positioning groove, and then the test sample is clamped between two anti-buckling parts and fixed by fasteners, and the fatigue test is performed on the fixed test sample.

[0010] The existing lubricating part positioning groove is in the shape of a strip, and the lubricating part cannot completely wrap the test sample between the two anti-buckling parts. A part of the test sample will be wrapped by the anti-buckling part, resulting in uneven force on the test sample, large test error, and inaccurate test results. The anti-buckling part of the present technical solution is provided with an I-shaped lubricating part positioning groove, and the shape of the lubricating part matches the shape of the lubricating part positioning groove. When the test sample is clamped in parallel between the two anti-buckling parts, the lubricating part can completely wrap the test sample located between the two anti-buckling parts. When the test sample is subjected to fatigue testing on a fatigue testing machine, the test sample is subjected to uniform force, the test error is reduced, and the test accuracy is improved.

[0011] This technical solution can be used to perform S min <0 axial stress, ε min For axial strain controlled fatigue test with a value of <0, different test methods can be selected according to actual conditions, and the scope of application is wide.

[0012] Furthermore, in step 2, S min The axial stress controlled fatigue test with a value of <0 uses axial load to control the test sample.

[0013] The beneficial effects of this solution are: this technical solution can perform S min Fatigue test with axial stress control of <0.

[0014] Furthermore, in step 2, ε min The axial strain controlled fatigue test of <0 is controlled by using a unidirectional extensometer or a bidirectional extensometer or an optical DIC device to control the test sample.

[0015] The beneficial effects of this solution are: this technical solution can select different test methods to test the test samples according to actual conditions. min The axial strain controlled fatigue test with a value of <0 has a wide range of applications.

[0016] Furthermore, in step 1, an extensometer positioning groove is provided on a side of each anti-buckling member away from the lubricating member positioning groove, and a unidirectional extensometer is fixed on the test sample through the extensometer positioning groove.

[0017] The beneficial effects of this solution are as follows: the anti-buckling member is provided with an extensometer positioning groove, and the ε min It is convenient to fix the extensometer when the axial strain is less than 0 and the fatigue test is controlled.

[0018] Furthermore, in step one, the anti-buckling device also includes a pressing plate, one side of the test sample is flush with the anti-buckling piece and is fixed using the pressing plate, and the other side of the test sample extends out of the anti-buckling piece by 1-2 mm, and the unidirectional extensometer is fixed on the test sample.

[0019] The beneficial effect of this solution is: when using a unidirectional extensometer to measure the test sample min When the axial strain is less than 0 and the fatigue test is controlled, one side of the test sample is made flush with the anti-buckling member. The purpose of this setting is: on the one hand, to minimize the test sample exposed on both sides of the anti-buckling member, so that the test sample is wrapped inside the anti-buckling member as much as possible, reducing the buckling probability of the test sample; on the other hand, it is convenient for fixing the pressing plate. Fix the pressing plate on the side of the test sample that is flush with the anti-buckling member, and fix the unidirectional extensometer on the side of the test sample that extends out. When using the unidirectional extensometer to measure the ε min When the axial strain is less than 0 and the fatigue test is controlled, the test sample can be prevented from moving laterally to the side where the unidirectional extensometer is not installed, thereby reducing the test error and improving the test accuracy.

[0020] Furthermore, in step 1, a central threaded hole is provided on a side of each anti-buckling member away from the lubricating member positioning groove, and a fixing rod is detachably connected to the central threaded hole to fix the bidirectional extensometer on the fixing rod.

[0021] The beneficial effects of this solution are as follows: the anti-buckling member is provided with a central threaded hole, a fixing rod is connected to the central threaded hole, and the test sample is tested using a bidirectional extensometer. min It is convenient to fix the bidirectional extensometer when the axial strain is less than 0 and the fatigue test is controlled.

[0022] Furthermore, in step 1, the length of each side of the test sample extending out of the anti-buckling member is 1-2 mm, and a bidirectional extensometer is fixed to each side of the test sample.

[0023] The beneficial effect of this solution is that the anti-buckling parts extend from both sides of the test sample, which is convenient for the installation of bidirectional extensometer. min Compared with the axial strain control fatigue test with a value of <0, this technical solution uses a bidirectional extensometer to perform ε min In the fatigue test controlled by axial strain less than 0, the average value is taken as the control parameter of the test, which reduces the test error and improves the accuracy of the test.

[0024] Using a bidirectional extensometer to test the specimen ensures uniform stress on both sides of the anti-buckling member, preventing lateral movement. Furthermore, the national standard GB / T26077-2021 stipulates that when performing fatigue tests on plate-like materials, it is recommended to use a bidirectional extensometer to test the specimen, and take the average value as the control parameter for the test. If this condition is not met, a unidirectional extensometer can be used.

[0025] Furthermore, in step one, when conducting an optical DIC strain-controlled fatigue test, the anti-buckling device also includes a light source device and a camera. Speckle is sprayed on one side or both sides of the test sample, and a pure color different from the speckle color is sprayed on the anti-buckling part and the lubricating part. The light source device is used to irradiate the test sample after the speckle is sprayed. The camera is closed-loop connected to the controller of the fatigue testing machine, and the camera and the controller of the fatigue testing machine maintain the same sampling frequency.

[0026] The beneficial effects of this solution are as follows: This technical solution uses a camera to take real-time photos and calculate the strain occurring in the area, which is converted into an electrical signal and then input into the controller of the fatigue testing machine. The controller of the fatigue testing machine converts the electrical signal transmitted in real time into strain and controls the operation of the fatigue testing machine. The sampling frequency of the camera and the controller of the fatigue testing machine needs to be consistent to improve the stability and accuracy of the test.

[0027] This technical solution sprays a pure color different from the speckle color on the anti-buckling part and the lubricating part, which can prevent the anti-buckling part and the lubricating part from affecting the image collected by the camera and affecting the accuracy of the test.

[0028] Compared with fatigue tests performed on test samples using unidirectional or bidirectional extensometers, the blade of the extensometer will leave marks on the test sample when using unidirectional or bidirectional extensometers. The marks left will cause microcracks to initiate prematurely and cause crack propagation, making the test sample prone to breakage. However, when using DIC equipment to perform fatigue tests on test samples, the camera and the test sample are non-contact tests, and the camera will not cause damage to the test sample. At the same time, during the test, the test sample will not move laterally, reducing the error of the test sample and improving the test accuracy.

[0029] Furthermore, in step 1, both sides of the test sample overlap with the anti-buckling member.

[0030] The beneficial effect of this solution is that since both sides of the test sample overlap with the anti-buckling member, the anti-buckling member completely wraps both sides of the test sample, thereby reducing the buckling probability of the test sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a three-dimensional diagram of the anti-buckling device in Example 1 of the present invention;

[0032] Figure 2 1 is an exploded view of the anti-buckling device in Example 1 of the present invention;

[0033] Figure 3 A three-dimensional diagram of the anti-buckling device in Example 2 of the present invention;

[0034] Figure 4 1 is an exploded view of the anti-buckling device in Example 2 of the present invention;

[0035] Figure 5 This is a stress-strain hysteresis curve diagram of the half-life of the test sample of the present invention when the thickness is 0.6 mm and the fatigue life is less than 1000 times;

[0036] Figure 6 This is a half-life strain-life curve diagram of the test sample of the present invention when the thickness is 0.6 mm and the fatigue life is less than 1000 times;

[0037] Figure 7 This is a half-life load-life curve diagram of the present invention when the test sample thickness is 0.6 mm and the fatigue life is less than 1000 times;

[0038] Figure 8 This is a stress-strain hysteresis curve diagram of the half-life of the test sample of the present invention when the thickness is 1.4 mm and the fatigue life is less than 1000 times;

[0039] Figure 9 This is a half-life strain-life curve diagram of the test sample of the present invention when the thickness is 1.4 mm and the fatigue life is less than 1000 times;

[0040] Figure 10 This is a half-life load-life curve diagram of the present invention when the thickness of the test sample is 1.4 mm and the fatigue life is less than 1000 times. DETAILED DESCRIPTION

[0041] The following is further described in detail through specific implementation methods:

[0042] The figure marks in the drawings of the specification include: anti-buckling part 1, pressure plate 2, fastening bolt 3, gasket 4, fastening nut 5, upper clamping part 6, lower clamping part 7, anti-buckling part 8, clamping section 9, fixing section 10, bolt hole 11, test sample 12, lubricating part positioning groove 13, lubricating part 14, extensometer positioning groove 15, extensometer 16, positioning block 17, test sample positioning groove 18, anti-buckling part positioning groove 19, correction block 20, center threaded hole 21, fixing rod 22.

[0043] Example 1

[0044] like Figure 1-2The anti-buckling device shown includes an anti-buckling member 1, a pressure plate 2, a fastener, and a positioning unit. In this embodiment, the anti-buckling member 1 is made of titanium alloy, and the fasteners are bolt fasteners. Specifically, there are four sets of bolt fasteners, each set of which includes a fastening bolt 3, a washer 4, and a fastening nut 5.

[0045] like Figure 2 As shown, there are two anti-buckling members 1, each of which is a symmetrical I-shaped plate structure. The two anti-buckling members 1 are attached to each other and connected by bolt fasteners. Each anti-buckling member 1 includes an upper clamping portion 6, a lower clamping portion 7 and an anti-buckling portion 8. The anti-buckling portion 8 is located between the upper clamping portion 6 and the lower clamping portion 7. The upper clamping portion 6 and the lower clamping portion 7 have the same structure, and the upper clamping portion 6, the lower clamping portion 7 and the anti-buckling portion 8 are integrally formed. Both the upper clamping portion 6 and the lower clamping portion 7 include a clamping section 9 and two fixing sections 10. The fixing sections 10 are located on either side of the clamping section 9 and are integrally formed with the clamping section 9. The fixing sections 10 are cylindrical in shape. The distance from the upper surface of the clamping section 9 to the plane containing the top of the fixing sections 10 is equal to the distance from the lower surface of the clamping section 9 to the plane containing the bottom of the fixing sections 10. The height of the clamping section 9 is less than the diameter of the fixing sections 10. Each fixing section 10 has a bolt hole 11 at its center. The purpose of the fixing sections 10 is to stagger the fixing sections 10 with the upper clamping portion 6 and the lower clamping portion 7, reducing the height of the upper clamping portion 6 and the lower clamping portion 7, thereby reducing the length of the test sample 12, reducing the probability of buckling of the test sample 12 during the test, and improving test accuracy. The purpose of the bolt holes 11 is to ensure that the bolt holes 11 are on the same horizontal plane as the clamping section 9, so that the bolt fastener can stably secure the test sample 12 between the two anti-buckling members 1.

[0046] like Figure 2 As shown, a test specimen 12 is clamped parallel to and held between two anti-buckling members 1. A lubricant positioning groove 13 is defined on the anti-buckling member 1 on the side of the test specimen 12. This groove 13 is I-shaped and comprises an upper horizontal portion, a vertical portion, and a lower horizontal portion, which are sequentially connected. The upper horizontal portion is located on the upper clamping portion 6, the horizontal portion is located on the lower clamping portion 7, and the vertical portion is located on the anti-buckling member 8. A lubricant 14 is provided between the test specimen 12 and the lubricant positioning groove 13. The shape of lubricant 14 matches that of lubricant positioning groove 13 and is bonded to the groove 13. Lubricant 14 is a polytetrafluoroethylene film with a thickness of 0.5-2.0 mm. In this embodiment, the thickness of lubricant 14 is 1.0 mm.

[0047] like Figure 2As shown, an extensometer positioning groove 15 is provided on the side of the anti-buckling portion 8 away from the lubricating element positioning groove 13. There are two extensometer positioning grooves 15 on each anti-buckling portion 8. The extensometer positioning grooves 15 are arc-shaped to prevent the rubber band on the extensometer 16 from breaking due to stress concentration when it is in a taut state. At the same time, the extensometer 16 can be longitudinally positioned during the test to prevent the extensometer 16 from longitudinally shifting. Figure 1 As shown, the left side of the test sample 12 is flush with the anti-buckling portion 8 and is fixed using the pressing plate 2. The right side of the test sample 12 extends beyond the anti-buckling portion 8 by 1-2 mm. The extensometer 16 is fixed to the test sample 12. In this embodiment, the length of the test sample 12 extending beyond the anti-buckling portion 8 is 1.5 mm.

[0048] like Figure 2 As shown, the positioning unit includes a positioning block 17 and a correction block 20. There are two positioning blocks 17 and two correction blocks 20. The two positioning blocks 17 are identical plate-shaped structures and are located on the upper and lower sides of the anti-buckling member 1. The right side of the positioning block 17 is provided with a test sample positioning groove 18 and an anti-buckling member positioning groove 19. The front and rear sides of the test sample positioning groove 18 are engraved with scales. The correction block 20 is L-shaped, with scales engraved on the wide side of the correction block 20. The correction block 20 can be clamped on the front and rear sides of the test sample positioning groove 18 so that the scales on the wide side of the correction block 20 coincide with the scales on the positioning block 17. The positioning block 17 cooperates with the correction block 20 to position the test sample 12 longitudinally and transversely.

[0049] By setting the lubricating member positioning groove 13 on the anti-buckling member 1 into an I-shape and allowing the lubricating member 14 to wrap the test sample 12 between the two anti-buckling members 1, the force on the test sample 12 is made more uniform. At the same time, since the left side of the test sample 12 is flush with the anti-buckling portion 8, the anti-buckling device can perform strain-controlled fatigue tests on test samples 12 with a thickness of 0.6mm-2.5mm. Figure 5-7 It can be seen that when the thickness of the test sample 12 is 0.6 mm, the entire test procedure is continuous and without abnormalities, and a smooth and undistorted hysteresis loop can be obtained, and there is no visible buckling phenomenon. It should be noted that: Figure 6 The upper curve represents the strain peak (%), and the lower curve represents the strain valley (%). Figure 7 The upper curve represents the peak load (kN), and the lower curve represents the valley load (kN); Figure 8-10 It can be seen that when the thickness of the test sample 12 is 1.4 mm and the strength is relatively high, the entire test process is continuous and without abnormalities, and a smooth and non-distorted hysteresis loop can be obtained, and there is no visible buckling phenomenon. It should be noted that: Figure 9The upper curve in the middle represents the strain peak (%), and the lower curve represents the strain valley value (%); Figure 10 The upper curve in the middle represents the peak load value (kN), and the lower curve represents the valley load value (kN); this shows that the anti-buckling device can test the test sample 12 with a thickness ranging from 0.6 mm to 2.5 mm and a tensile strength less than 2500 MPa.

[0050] The specific implementation process is as follows:

[0051] In this embodiment, a unidirectional extensometer is used to measure the ε min The axial strain controlled fatigue test of <0 specifically includes the following steps:

[0052] Step 1: Fix the test sample 12 on the anti-buckling device, such as Figure 2 As shown, the lubricating element 14 is first bonded into the lubricating element positioning groove 13. The left anti-buckling element 1 is then placed into the anti-buckling element positioning grooves 19 on the two positioning blocks 17, with the lubricating element 14 on the same side as the test sample positioning groove 18. The test sample 12 is then placed into the test sample positioning groove 18. Since the rear side of the test sample 12 is flush with the anti-buckling portion 8, a suitable correction block 20 is selected and inserted into the test sample positioning groove 18 on the rear side of the positioning block 17, so that the rear side of the test sample 12 abuts against the correction block 20. The test sample 12 is then positioned horizontally and vertically using the scales on the positioning blocks 17 and correction blocks 20, so that the test sample 12 is flush with the rear side of the anti-buckling portion 8. The right anti-buckling element 1 is then attached to the left anti-buckling element 1. The two anti-buckling elements 1 are then secured together using bolts. The secured anti-buckling device is then removed from the positioning blocks 17 and correction blocks 20.

[0053] Step 2: Use a unidirectional extensometer to measure the ε min <0 axial strain controlled fatigue test, specifically, as Figure 1 As shown, the extensometer 16 is fixed to the extensometer positioning groove 15 by a rubber band or other elastic band, and the blade on the extensometer 16 is in contact with the test sample 12. The pressing plate 2 is fixed to the left side of the anti-buckling part 10 by a rubber band or other elastic band, and the test sample 12 is pressed tightly. min In the fatigue test controlled by axial strain of 0, the real-time strain is calculated by the gauge length of the extensometer 16 and the displacement of the opening / closing of the blade during the test and is used as the control parameter.

[0054] Example 2

[0055] Different from Example 1, Figure 3 、 Figure 4As shown, the number of extensometers 16 is two.

[0056] like Figure 3 As shown, the length of the test sample 12 extending from the anti-buckling portion 8 on both sides is 1-2 mm. In this embodiment, the length of the test sample 12 extending from the anti-buckling portion 8 on both sides is 1.5 mm, which facilitates the fixing of the extensometer 16 on the test sample 12 on the left and right sides of the anti-buckling portion 8. Figure 4 As shown, a central threaded hole 21 is formed on the side of the anti-buckling portion 8 away from the lubricating element positioning groove 13 , and a fixing rod 22 is connected to the inner thread of the central threaded hole 21 to facilitate fixing the bidirectional extensometer 16 on the fixing rod 22 .

[0057] The specific implementation process is as follows:

[0058] The test sample 12 was tested using a bidirectional extensometer. min The steps of the axial strain controlled fatigue test are:

[0059] Step 1: Fix the test sample 12 on the anti-buckling device, such as Figure 4 As shown, since the anti-buckling parts 8 extend out from both the left and right sides of the test sample 12, a suitable correction block 20 is selected, and the two correction blocks 20 are respectively clamped on the front and rear sides of the test sample positioning groove 18, and the test sample 12 in the test sample positioning groove 18 is clamped so that the test sample 12 is in the middle position of the anti-buckling piece 1, and the anti-buckling piece 1 on the right is attached to the anti-buckling piece 1 on the left, and the two anti-buckling pieces 1 are fixed together by bolt fasteners, and the fixed anti-buckling device is removed from the positioning block 17 and the correction block 20.

[0060] Step 2: Use a bidirectional extensometer to measure the ε min <0 axial strain controlled fatigue test, specifically, as Figure 3 As shown, two extensometers 16 are respectively installed on the test sample 12 on the left and right sides of the anti-buckling part 8, and the extensometers 16 are fixed to the fixing rod 22 through rubber bands or other elastic bands so that the blades on the extensometers 16 are in contact with the test sample 12. The installed test sample 12 is removed from the positioning block 17 and the test sample 12 is subjected to ε min For fatigue test controlled by axial strain <0, the average value is taken as the control parameter of the test.

[0061] Example 3

[0062] In this embodiment, optical DIC is used to perform ε minIn the axial strain controlled fatigue test with an axial strain of 0.004 mm / s and an axial strain of 0.004 mm / s, the anti-buckling device further comprises a light source device and a camera. Speckle is sprayed on one or both sides of the test sample 12. A solid color different from the speckle color is sprayed on the anti-buckling member 1 and the lubricating member 14. The light source device is used to illuminate the test sample 12 after the speckle is sprayed. The camera is connected in a closed loop to the controller of the fatigue testing machine, and the camera and the controller of the fatigue testing machine maintain the same sampling frequency.

[0063] The specific implementation process is as follows:

[0064] Step 1: Fix the test sample 12 on the anti-buckling device. Specifically, different from Example 2, both sides of the test sample 12 overlap with the anti-buckling parts 8.

[0065] Step 2: Use optical DIC equipment to measure the test sample 12 min <0 axial strain controlled fatigue test, specifically, when it is necessary to use a camera to capture an image of one side of the test sample 12, a speckle pattern is sprayed on the side of the test sample 12, and a solid color different from the speckle color is sprayed on the anti-buckling member 1 and the lubricating member 14 on the side. The camera is fixed on the test sample 12 The intensity of the light source is adjusted so that the camera can clearly capture the image of the test sample 12 on that side. The camera takes real-time photos and calculates the strain occurring in the area. The resulting signals are then input into the fatigue testing machine controller. The fatigue testing machine controller converts the real-time transmitted signals into strain and controls the operation of the fatigue testing machine. When it is necessary to use the camera to capture images of both sides of the test sample 12, speckle patterns are sprayed on both sides of the test sample 12, and a solid color different from the speckle pattern is sprayed on the anti-buckling member 1 and the lubricating member 14. Two cameras are fixed to the sides of the test sample 12 to capture images of both sides of the test sample 12. The intensity of the light source is adjusted so that the optical DIC device can clearly capture the image of the test sample 12 on that side. The camera takes real-time photos and calculates the strain occurring in the area. The resulting signals are then input into the fatigue testing machine controller. The fatigue testing machine controller converts the real-time transmitted signals into strain and controls the operation of the fatigue testing machine. Depending on the actual situation, one camera or two cameras can be used for the test.

[0066] Example 4

[0067] S was performed on the test sample 12. min The steps of the axial stress controlled fatigue test are:

[0068] Step 1: Fix the test sample 12 on the anti-buckling device, which is the same as Example 3.

[0069] Step 2: Use a fatigue testing machine to test the test sample 12min In the fatigue test with axial stress controlled at <0, the peak and valley values ​​of the load are used as the control parameters.

[0070] The above are only embodiments of the present invention, and common knowledge such as the specific technical solutions and / or characteristics in the solutions are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for fatigue testing of plate-like materials, characterized by: The following steps are involved: Step 1: Fix the test sample on the anti-buckling device, which includes two anti-buckling parts and four sets of fasteners. Each anti-buckling part is provided with an I-shaped lubricating part positioning groove. A lubricating part is provided in the lubricating part positioning groove, and the shape of the lubricating part matches the shape of the lubricating part positioning groove. The test sample is clamped in parallel between the two lubricating parts and fixed by fasteners. Each anti-buckling part includes an upper clamping part, a lower clamping part and an anti-buckling part. The upper clamping part and the lower clamping part each include a clamping section and two fixed sections. The fixed sections are located on both sides of the clamping section. The fixed section is cylindrical. The distance from the upper surface of the clamping section to the plane where the top of the fixed section is located is equal to the distance from the lower surface of the clamping section to the plane where the bottom of the fixed section is located. The height of the clamping section is less than the diameter of the fixed section. A bolt hole is provided at the center of each fixed section. Step 2: Use fatigue testing machine to test the sample min <0 axial stress, ε min <0 axial strain controlled fatigue test.

2. The method for fatigue testing of plate-shaped materials according to claim 1, characterized in that: In step 2, S min The axial stress controlled fatigue test with a value of <0 uses axial load to control the test sample.

3. The method for fatigue testing of plate-shaped materials according to claim 1, characterized in that: In step 2, ε min The axial strain controlled fatigue test of <0 is controlled by using a unidirectional extensometer or a bidirectional extensometer or an optical DIC device to control the test sample.

4. A plate material fatigue test method according to claim 3, characterized in that: In step 1, an extensometer positioning groove is provided on a side of each anti-buckling member away from the lubricating member positioning groove, and a unidirectional extensometer is fixed on the test sample through the extensometer positioning groove.

5. The method for fatigue testing of plate-shaped materials according to claim 4, characterized in that: In step 1, the anti-buckling device also includes a pressing plate. One side of the test sample is flush with the anti-buckling piece and is fixed with the pressing plate. The other side of the test sample extends out of the anti-buckling piece by 1-2 mm. The unidirectional extensometer is fixed on the test sample.

6. The method for fatigue testing of plate-shaped materials according to claim 3, characterized in that: In step 1, a central threaded hole is provided on a side of each anti-buckling member away from the lubricating member positioning groove, and a fixing rod is detachably connected to the central threaded hole to fix the bidirectional extensometer on the fixing rod.

7. The method for fatigue testing of plate-shaped materials according to claim 6, characterized in that: In step 1, the length of each side of the test sample extending out of the anti-buckling member is 1-2 mm, and a bidirectional extensometer is fixed on both sides of the test sample.

8. The method for fatigue testing of plate-shaped materials according to claim 3, characterized in that: In step one, when conducting an optical DIC strain-controlled fatigue test, a control system is also included. The control system includes a light source device and a camera. Speckle is sprayed on one or both sides of the test sample, and a pure color different from the speckle color is sprayed on the anti-buckling part and the lubricating part. The light source device is used to irradiate the test sample after the speckle is sprayed. The camera is closed-loop connected to the controller of the fatigue testing machine, and the camera and the controller of the fatigue testing machine maintain the same sampling frequency.

9. The method for fatigue testing of plate-shaped materials according to claim 8, characterized in that: In step 1, both sides of the test specimen overlap with the buckling restraints.

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