A method and tool for large strain shear testing of low modulus foamed elastomeric materials

Abstract

The low modulus foamed elastic material large strain shear test method provided by the application is characterized in that: a test piece is formed by bonding a middle plate, two side plates and two test blocks, and is prepared by adopting a process of "sampling flattening + metal sand blasting treatment + special bonding system", and the whole is a three-plate symmetrical shear structure; during the test, longitudinal stretching is formed to make the two test blocks bear stress uniformly, produce symmetrical and uniform pure shear large strain deformation, ensure that the test blocks do not fall off during 150% large strain cyclic stretching, real-time monitoring of stress in three directions is realized by using a transverse sensor, force decoupling is formed, effective separation of longitudinal force and transverse force is realized, transverse force data is accurately obtained, the force coupling problem of a traditional single-way sensor is eliminated, the test precision and stability are significantly improved, and accurate and stable test of the large strain shear performance of the foamed elastic material is realized, thereby providing complete mechanical basis for simulation analysis, structure design and service life evaluation. The application also provides a low modulus foamed elastic material large strain shear test tool.

Description

Technical Field

[0001] This invention relates to a method for testing large strain shear in low-modulus foamed elastic materials, belonging to the technical field of elastic material shear testing. This invention also relates to a fixture for testing large strain shear in low-modulus foamed elastic materials. Background Technology

[0002] Foamed elastic materials (such as polyurethane foam, rubber foam, and silicone foam) are widely used in rail transportation, new energy, engineering machinery, and high-end equipment due to their excellent cushioning, vibration reduction, sealing, and fatigue resistance properties. In actual service, these materials not only withstand conventional compressive and tensile loads but also frequently experience complex stress states such as lateral support, interface slippage, cyclic shearing, and compound torsion. Shear performance is a core mechanical indicator determining their structural reliability, service life, and safety limits. Currently, some standards and techniques have been established for testing the shear performance of foamed and rubber materials, but all have significant limitations: ISO 1922 and GB / T 10007 mainly specify the shear test of rigid foamed plastics, which are only applicable to high modulus and small deformation rigid foams and cannot be adapted to low modulus and large deformation soft foamed elastic materials. ISO 1827 and GB / T 12830 are used to determine the shear modulus and adhesive strength between rubber and rigid sheet materials, focusing on interfacial bonding performance, but cannot directly characterize the bulk shear mechanical behavior of pure foamed elastic materials. ASTM C273 and GB / T 1455 are for shear tests on core materials of sandwich structures, and are applicable to rigid foams only. They are not applicable to soft, highly ductile foamed elastic materials.

[0003] In summary, existing standards and testing techniques lack specific methods for testing the shear properties of low-modulus, high-deformation foamed elastic materials, resulting in the following shortcomings in practical testing: 1) Traditional methods only measure longitudinal force and longitudinal deformation, and cannot achieve simultaneous acquisition of lateral force, resulting in incomplete mechanical characterization; 2) When using conventional unidirectional force sensors to measure lateral loads, force coupling interference is prone to occur, leading to distorted test results and insufficient accuracy; 3) Low-modulus, low-density foamed elastic materials are difficult to sample, with poor specimen regularity and surface flatness, resulting in low sample preparation efficiency and difficulty in ensuring data consistency. 4) During high strain (>150%) shearing, the bonding strength between the foamed material and the metal loading surface is insufficient, and interface debonding is very likely to occur, making it impossible to complete the effective test. Summary of the Invention

[0004] This invention provides a method for testing the large strain shear of low-modulus foamed elastic materials. The test specimen consists of a middle plate, two side plates, and two bonded test blocks. It is prepared using a process of "sampling and leveling + metal sandblasting + a special bonding system," resulting in a three-plate symmetrical shear structure. During testing, the testing machine pulls the middle plate to create longitudinal tension, ensuring uniform stress on the two test blocks and generating symmetrical and uniform pure shear large strain deformation. This stable deformation avoids eccentric loading and stress concentration, offsets additional bending moments, and ensures no debonding during 150% large strain cyclic tensile testing. A transverse sensor monitors the forces in three directions in real time, achieving force decoupling and effectively separating longitudinal and transverse forces. This accurately obtains transverse force data, eliminating the force coupling problem of traditional unidirectional sensors, significantly improving testing accuracy and stability. This method enables accurate and stable testing of the large strain shear performance of foamed elastic materials, providing a complete mechanical basis for simulation analysis, structural design, and life assessment. This invention also provides a fixture for testing the large strain shear of low-modulus foamed elastic materials.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for testing large strain shear in low-modulus foamed elastic materials, characterized by comprising the following steps: Material selection: Cut two rectangular test blocks of the same size from low-modulus foamed elastic material products or semi-finished products. Prepare two side plates and one middle plate. The side plates and middle plate are made of stainless steel, and their thickness is less than that of the test blocks, while their length and width are greater than that of the test blocks. Sample preparation: Two test blocks are symmetrically bonded between the middle plate and the side plate, with the left and right sides of the test blocks covered by the middle plate and the side plate to form a test specimen; Determine the test fixture: Assemble the base connected to the lower base of the testing machine and the fixture mounted on the base into a test fixture. Install a transverse sensor that can measure the transverse force of the test piece on the fixture. The fixture includes a left clamping plate and a right clamping plate that are respectively fixed vertically to the base by bolts. The transverse sensor is fixed on the right clamping plate. A sensor transition plate is fixed on the transverse sensor. The test piece is clamped between the left clamping plate and the sensor transition plate. One side plate is positioned on the left clamping plate and the other side plate is positioned on the sensor transition plate. Clamping: Clamp the test piece on the fixture, position the side plate on the fixture, set the middle plate vertically, and connect the middle plate and the base to the upper and lower bases of the testing machine respectively. Connect the longitudinal sensor for measuring the applied load, the displacement sensor for measuring the motion displacement, and the transverse sensor on the testing machine to the position. Shear strain test: Start the testing machine, and the upper base of the testing machine pulls the middle plate upward, causing the specimen to undergo shear deformation; Result calculation: Based on the dimensions of the specimen, the real-time data from the transverse sensor and the sensors on the testing machine, and combined with the shear strain ε, shear stress σ, and transverse stress... The calculation formula yields the shear strain ε, shear stress σ, and transverse stress corresponding to the specimen. ; The formula for calculating shear strain ε is: , in This represents the vertical change. The initial thickness of the test block; The formula for calculating shear stress σ is: , in For longitudinal force, W is the initial length of the test block, and W is the initial width of the test block; Transverse stress The calculation formula is: , in It is a lateral force. is the initial length of the test block, and w is the initial width of the test block.

[0006] The preferred sample preparation process is as follows: First, measure the dimensions of the test block and check its quality. The length of the test block should be 25±1mm, the width should be 14±1mm, and the thickness should be 14±1mm. The test block should be free of rubber skin and have a smooth, defect-free surface. The parallelism and flatness tolerances between the two bonding surfaces of the test block should not exceed 0.5mm. Then, the bonding surfaces of the middle plate and side plates are roughened by sandblasting to increase the bonding strength with the adhesive. Next: Mark the bonding positions of the test blocks on the side plates and the middle plate respectively; Finally, apply adhesive to the side of the test block and then attach the test block to the joint between the middle plate and the side plate. Let it cure at room temperature for no less than 24 hours to obtain the test piece.

[0007] Preferably, the adhesive is a cyanoacrylate adhesive.

[0008] Preferably, the strain levels for shear strain testing are 30%, 50%, 70%, 100%, 150%, and 200%, and the testing machine cyclically loads the test piece at least 5 times at each strain level, with a strain rate of 1% / s for each loading.

[0009] A fixture for testing large strain shear of low modulus foamed elastic material, used to realize the above-mentioned method for testing large strain shear of low modulus foamed elastic material, characterized in that it includes a base connected to the lower base of the testing machine and a clamp mounted on the base. The fixture includes a left clamping plate and a right clamping plate that are vertically fixed to the base by bolts, a transverse sensor is fixed on the right clamping plate, a sensor transition plate is fixed on the transverse sensor, the test piece is clamped between the left clamping plate and the sensor transition plate, one side plate is positioned on the left clamping plate, and the other side plate is positioned on the sensor transition plate.

[0010] Preferably, the top of the middle plate is higher than the side plate and has a connecting hole. The connecting hole is connected to the upper base of the testing machine through a pin. A transition joint is fixed on the bottom surface of the base along the vertical direction. The transition joint is connected to the lower base of the testing machine through a pin.

[0011] Preferably, the base and the left and right clamps are guided together, and a strip-shaped through hole is opened on the base. The left and right clamps are fixed to the base by bolts that extend into the strip-shaped through hole.

[0012] Preferably, the lateral sensor is a three-dimensional load sensor.

[0013] Preferably, grooves that mate with the side plates are provided on both the left clamping plate and the sensor transition plate, the side plates are inserted into the grooves, and the tops of both the left clamping plate and the sensor transition plate are fitted with tightening bolts, the lower ends of the tightening bolts being pressed against the top surface of the side plates.

[0014] The beneficial effects of the invention are: In the large strain shear test method for low-modulus foamed elastic materials of the present invention, the test specimen is composed of a middle plate, two side plates and two test blocks bonded together, forming a three-plate symmetrical shear structure, forming a pure shear stress system. The two test blocks are cuboids, and the surface of the test blocks should be flat and smooth without burrs, depressions or protrusions or other obvious defects. The parallelism and flatness tolerance between the two bonded surfaces of the test blocks should not exceed 0.5 mm. The test blocks are sampled from low-modulus foamed elastic material products or semi-finished products. According to the hardness of the test blocks, they are cut by CNC machine tool slicing, vertical cutting machine or engraving machine to obtain test blocks, thereby improving sample preparation efficiency and ensuring the consistency of test block size data. The side and middle plates are made of stainless steel, capable of withstanding 5kN without deformation, with a smooth, non-warping surface. Before gluing, they undergo sandblasting to roughen the surface and increase bonding strength. The middle plate, side plates, and test block are bonded together to form the test specimen. During testing, the testing machine pulls the middle plate to create longitudinal tension, ensuring uniform force on both test blocks, resulting in symmetrical and uniform pure shear strain deformation. This stable deformation avoids eccentric loading and stress concentration, offsets additional bending moments, and guarantees a pure shear state, improving the accuracy and repeatability of test data. A transverse sensor is installed on the fixture to monitor the transverse (Z-direction) force on the test specimen in real time, while a longitudinal sensor on the machine base monitors the longitudinal (X-direction) force. During testing, the forward / backward (Y-direction) force on the test block is essentially zero, achieving force decoupling and effectively separating longitudinal and transverse forces. This allows for accurate acquisition of transverse force data, eliminating the force coupling problem of traditional unidirectional sensors and significantly improving test accuracy and stability. Accurate measurement of the initial dimensions of the test block is crucial before testing. The shear strain calculation formula... The longitudinal change of the specimen is obtained by real-time detection of the upward displacement of the middle plate by the displacement sensor on the testing machine. The longitudinal force in the calculation formula of shear stress is obtained by real-time detection of the longitudinal sensor on the testing machine, and the transverse force in the calculation formula of transverse stress is obtained by real-time detection of the transverse sensor. The shear strain, shear stress and transverse stress of the specimen under large strain deformation are calculated, realizing accurate and stable testing of the large strain shear performance of foamed elastic materials, and providing a complete mechanical basis for simulation analysis, structural design and life assessment.

[0015] In the high-strain shear testing fixture for low-modulus foamed elastic materials of the present invention, the left clamping plate and the left clamping plate are vertically fixed on the base. A transverse sensor is fixed on the side of the right clamping plate facing the left clamping plate, and a sensor transition plate is fixed on the transverse sensor. The test piece is clamped between the left clamping plate and the sensor transition plate. The left side plate is positioned on the left clamping plate, and the right side plate is positioned on the sensor transition plate. When the upper base of the testing machine pulls the middle plate upward, since both side plates are positioned, the upward movement of the middle plate causes the two test pieces to undergo symmetrical and uniform pure shear deformation. The greater the longitudinal load applied by the testing machine, the greater the shear strain of the test piece. Multiple strain levels can be used to test the test. Alternatively, the longitudinal load applied by the testing machine, the longitudinal displacement of the middle plate, and the longitudinal movement speed during the test can be determined according to the working conditions of the test piece. The transverse sensor monitors the transverse (Z-direction) force on the test piece in real time, while the longitudinal sensor on the test machine base monitors the longitudinal (X-direction) force on the test piece. This force decoupling effectively separates the longitudinal and transverse forces, accurately obtains transverse force data, eliminates the force coupling problem of traditional unidirectional sensors, and significantly improves test accuracy and stability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the test fixture in this invention.

[0017] Figure 2 This is an exploded view of the test fixture.

[0018] Figure 3 for Figure 2 The front view.

[0019] Figure 4 This is a photograph of the actual test piece. Detailed Implementation

[0020] The following is combined with Figures 1-4 The embodiments of the present invention will be described in detail below.

[0021] A method for testing large strain shear in low-modulus foamed elastic materials, characterized by comprising the following steps: Material selection: Cut two rectangular test blocks 100 of the same size from low modulus foamed elastic material products or semi-finished products. Prepare two side plates 5 and one middle plate 6. Both side plates 5 and middle plate 6 are made of stainless steel, and their thickness is less than that of test block 100. Their length and width are greater than that of the test block. Sample preparation: Two test blocks, approximately 100mm in size, are symmetrically bonded between the middle plate 6 and the side plate 5. The left and right sides of the test blocks are covered by the middle plate and the side plate to form test piece 3. Determine the test fixture: Assemble the base 1 connected to the lower base of the testing machine and the fixture 2 mounted on the base 1 into a test fixture. Install a transverse sensor 4 on the fixture 2 to measure the transverse force of the test piece. The fixture 2 includes a left clamping plate 7 and a right clamping plate 8 that are respectively fixed vertically to the base 1 by bolts. The transverse sensor 4 is fixed on the right clamping plate 8. A sensor transition plate 9 is fixed on the transverse sensor 4. The test piece 3 is clamped between the left clamping plate 7 and the sensor transition plate 9. One side plate 5 is positioned on the left clamping plate 7 and the other side plate 5 is positioned on the sensor transition plate 9. Clamping: Clamp the test piece 3 on the fixture 2, position the side plate 5 on the fixture 2, set the middle plate 6 vertically, and connect the middle plate 6 and the base 1 to the upper and lower bases of the testing machine respectively. Connect the longitudinal sensor for measuring the applied load, the displacement sensor for measuring the motion displacement, and the transverse sensor on the testing machine to the position. Shear strain test: Start the testing machine, and the upper base of the testing machine pulls the middle plate upward, causing the specimen to undergo shear deformation; Result calculation: Based on the dimensions of the specimen, the real-time data from the transverse sensor and the sensors on the testing machine, and combined with the shear strain ε, shear stress σ, and transverse stress... The calculation formula yields the shear strain ε, shear stress σ, and transverse stress corresponding to the specimen. ; The formula for calculating shear strain ε is: , in This represents the vertical change. The initial thickness of the test block; The formula for calculating shear stress σ is: , in For longitudinal force, W is the initial length of the test block, and W is the initial width of the test block; Transverse stress The calculation formula is: , in It is a lateral force. is the initial length of the test block, and w is the initial width of the test block.

[0022] In the above-described method for testing large strain shear of low-modulus foamed elastic materials, the test piece 3 is composed of a middle plate 6, two side plates 5, and two test blocks 100 bonded together, forming a three-plate symmetrical shear structure and a pure shear stress system. The two test blocks are cuboids, and the surfaces of the test blocks should be flat and smooth without burrs, depressions, or protrusions or other obvious defects. The parallelism and flatness tolerances between the two bonded surfaces of the test block 100 should not exceed 0.5 mm. The test blocks are sampled from low-modulus foamed elastic material products or semi-finished products. Depending on the hardness of the test blocks, they are cut using a CNC machine tool, a vertical cutting machine, or a carving machine to improve sample preparation efficiency and ensure the consistency of the test block dimensional data. The side and middle plates are made of stainless steel, capable of withstanding 5kN without deformation, with a smooth, non-warping surface. Before gluing, they undergo sandblasting to roughen the surface and increase bonding strength. The middle plate, side plates, and test block are bonded together to form the test specimen. During testing, the testing machine pulls the middle plate 6 to create longitudinal tension, ensuring uniform force on both test blocks, resulting in symmetrical and uniform pure shear strain deformation. This stable deformation avoids eccentric loading and stress concentration, offsets additional bending moments, and guarantees a pure shear state, improving the accuracy and repeatability of test data. A transverse sensor is installed on fixture 3 to monitor the transverse (Z-direction) force on the test specimen in real time. A longitudinal sensor on the machine base monitors the longitudinal (X-direction) force on the test specimen. During testing, the forward and backward (Y-direction) force on the test block is essentially zero, achieving force decoupling and effectively separating longitudinal and transverse forces. This accurately obtains transverse force data, eliminating the force coupling problem of traditional unidirectional sensors and significantly improving test accuracy and stability. The initial dimensions of the test block are accurately measured before testing. The shear strain calculation formula... The longitudinal change of the specimen is obtained by real-time detection of the upward displacement of the middle plate by the displacement sensor on the testing machine. The longitudinal force in the calculation formula of shear stress is obtained by real-time detection of the longitudinal sensor on the testing machine, and the transverse force in the calculation formula of transverse stress is obtained by real-time detection of the transverse sensor. The shear strain, shear stress and transverse stress of the specimen under large strain deformation are calculated, realizing accurate and stable testing of the large strain shear performance of foamed elastic materials, and providing a complete mechanical basis for simulation analysis, structural design and life assessment.

[0023] The specific process for sample preparation is as follows: First, measure the dimensions of the test block 100 and check its quality. The length of the test block is 25±1mm, the width is 14±1mm, and the thickness is 14±1mm. The test block should not have a rubber skin and the surface should be smooth and free of defects. The parallelism and flatness tolerance between the two bonding surfaces of the test block should not exceed 0.5mm. Then, the bonding surfaces of the middle plate 6 and the side plate 5 are roughened by sandblasting to increase the bonding strength with the adhesive. Next: Mark the bonding positions of the test blocks on the side plate 5 and the middle plate 6 respectively; Finally, apply cyanoacrylate adhesive to the side of the test block 100, then attach the test block to the joint between the middle plate and the side plate, and cure at room temperature for no less than 24 hours to obtain the test piece.

[0024] The above sample preparation process employs a combination of "sampling and leveling + metal sandblasting + a dedicated adhesive system." Before bonding, the dimensions and quality of the test blocks are measured and inspected. The middle plate 6 and side plate 5 are roughened by sandblasting to improve bonding reliability. The bonding positions are marked on both side plate 5 and middle plate 6 to ensure symmetrical bonding of the test blocks between them. Recommended cyanoacrylate adhesives are used for bonding and cured at room temperature for at least 24 hours to ensure reliable bonding of test block 100 throughout the entire test. It must not detach during tests with strains greater than 150% and must not detach under 150% high-strain cyclic tensile testing, achieving multiple cyclic tensile tests without detachment. Alternatively, test block 100, middle plate 6, and side plate 5 can be vulcanized together at high temperature to form test piece 3.

[0025] The shear strain test includes strain levels of 30%, 50%, 70%, 100%, 150%, and 200%. At each strain level, the testing machine cyclically loads the test specimen at least 5 times, with a strain rate of 1% / s per loading. Preferably, the test strain levels are 30%, 50%, 70%, 100%, 150%, and 200%, and the testing machine cyclically loads the test specimen at least 5 times at each strain level for ease of operation. A strain rate of 1% / s refers to a strain rate of 0.01 mm / mm / s, or 0.01 s. -1 .

[0026] This invention also protects a high-strain shear testing fixture for low-modulus foamed elastic materials, used to implement the high-strain shear testing method for low-modulus foamed elastic materials described above. The fixture is characterized by including a base 1 connected to the lower base of the testing machine and a clamp 2 mounted on the base 1. The clamp 2 includes a left clamping plate 7 and a right clamping plate 8 that are respectively fixed vertically to the base 1 by bolts. A transverse sensor 4 is fixed on the right clamping plate 8. A sensor transition plate 9 is fixed on the transverse sensor 4. The test piece 3 is clamped between the left clamping plate 7 and the sensor transition plate 9. One side plate 5 is positioned on the left clamping plate 7, and the other side plate 5 is positioned on the sensor transition plate 9.

[0027] In the above-described fixture, the left clamping plate 7 and the left clamping plate 8 are vertically fixed on the base 1. The right clamping plate 8 is fixed with a transverse sensor 4 on the side facing the left clamping plate 7, and a sensor transition plate 9 is fixed on the transverse sensor 4. The test piece 3 is clamped between the left clamping plate 7 and the sensor transition plate 9. The left side plate 5 is positioned on the left clamping plate 7, and the right side plate 5 is positioned on the sensor transition plate 9. When the upper base of the testing machine pulls the middle plate upward 6, since both side plates 5 are positioned, the upward movement of the middle plate 6 causes the two test pieces 100 to undergo symmetrical and uniform pure shear deformation. The greater the longitudinal load applied by the testing machine, the greater the shear strain of the test piece. Multiple strain levels can be used to test the test, such as testing the test piece with strain levels of 30%, 50%, 70%, 100%, 150%, and 200% and determining the strain rate of the test piece during the test. Alternatively, the longitudinal load applied by the testing machine, the longitudinal displacement of the middle plate, and the longitudinal movement speed during the test can be determined according to the working conditions of the test piece. The transverse sensor monitors the transverse (Z-direction) force on the test piece in real time, while the longitudinal sensor on the test machine base monitors the longitudinal (X-direction) force on the test piece. This force decoupling effectively separates the longitudinal and transverse forces, accurately obtains transverse force data, eliminates the force coupling problem of traditional unidirectional sensors, and significantly improves test accuracy and stability.

[0028] The top of the middle plate 6 extends above the side plate and has a connecting hole 61. The connecting hole 61 is connected to the upper base of the testing machine via a pin. A transition joint 10, vertically arranged, is fixed on the bottom surface of the base 1 and is connected to the lower base of the testing machine via a pin. The middle plate 6 is directly connected to the upper base of the testing machine via a pin, and the transition joint 10 is connected to the lower base of the testing machine via a pin. When the upper base of the testing machine pulls the middle plate 6 upward, i.e., the upper base of the testing machine applies an upward load to pull the middle plate 6 upward, causing the test block 100 to undergo shear deformation. The upward load, upward movement speed, and movement displacement applied by the upper base of the testing machine are adjusted according to the testing requirements. When the test block 100 undergoes shear deformation, the sensor transition plate 9 is pulled by the test block 100, transmitting the shear force to the transverse sensor 4. The connection between the transverse sensor 4 and the sensor transition plate 9 and the test piece 3 achieves force decoupling, effectively separating the longitudinal shear force from the transverse force, accurately acquiring transverse force data, eliminating the force coupling problem of traditional unidirectional sensors, and significantly improving testing accuracy and stability.

[0029] The base 1 forms a guiding fit with both the left and right clamping plates, and a strip-shaped through hole 11 is provided on the base 1. The left and right clamping plates are fixed to the base 1 by bolts 12 extending into the strip-shaped through hole. The positions of the left clamping plate 7 and the right clamping plate 8 on the base 1 are adjustable, and the alignment of the left and right clamping plates is ensured by the guiding fit with the base 1. This ensures the reliability of clamping the test piece 3 and allows the fixture 2 to meet the clamping requirements of test pieces 3 of different thicknesses, so as to test the shear performance of test blocks of different specifications under large strain.

[0030] The lateral sensor 4 is a three-dimensional load sensor. The three-dimensional load sensor monitors the lateral (Z-direction) force on the test piece 3 in real time, while the longitudinal sensor on the test machine base monitors the longitudinal (X-direction) force on the test piece. This force decoupling effectively separates the longitudinal and lateral forces, accurately obtains lateral force data, eliminates the force coupling problem of traditional unidirectional sensors, and significantly improves test accuracy and stability.

[0031] In this design, grooves A are provided on both the left clamping plate 7 and the sensor transition plate 9 to mate with the side plates. The side plates 5 are inserted into grooves A. Tightening bolts 13 are fitted to the top of both the left clamping plate 7 and the sensor transition plate 9, with the lower ends of the tightening bolts 13 pressing against the top surface of the side plates. As shown in the figure, the grooves A of the left clamping plate 7 and the sensor transition plate 9 are positioned opposite each other. The side plates 5 of both plates are inserted into grooves A respectively. The tightening bolts 13 are used to position the side plates 5 in grooves A, preventing them from detaching. When the middle plate 6 is pulled upwards, because the side plates 5 are positioned in grooves A, the test block 100 will undergo shear deformation as the middle plate 6 moves upwards.

[0032] The technical solutions of the embodiments of the present invention have been fully described above with reference to the accompanying drawings. It should be noted that the described embodiments are only a part of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A method for testing large strain shear in low-modulus foamed elastic materials, characterized in that, Includes the following steps: Material selection: Cut two rectangular test blocks of the same size from low-modulus foamed elastic material products or semi-finished products. Prepare two side plates and one middle plate. The side plates and middle plate are made of stainless steel, and their thickness is less than that of the test blocks, while their length and width are greater than that of the test blocks. Sample preparation: Two test blocks are symmetrically bonded between the middle plate and the side plate, with the left and right sides of the test blocks covered by the middle plate and the side plate to form a test specimen; Determine the test fixture: Assemble the base connected to the lower base of the testing machine and the fixture mounted on the base into a test fixture. Install a transverse sensor that can measure the transverse force of the test piece on the fixture. The fixture includes a left clamping plate and a right clamping plate that are respectively fixed vertically to the base by bolts. The transverse sensor is fixed on the right clamping plate. A sensor transition plate is fixed on the transverse sensor. The test piece is clamped between the left clamping plate and the sensor transition plate. One side plate is positioned on the left clamping plate and the other side plate is positioned on the sensor transition plate. Clamping: Clamp the test piece on the fixture, position the side plate on the fixture, set the middle plate vertically, and connect the middle plate and the base to the upper and lower bases of the testing machine respectively. Connect the longitudinal sensor for measuring the applied load, the displacement sensor for measuring the motion displacement, and the transverse sensor on the testing machine to the position. Shear strain test: Start the testing machine, and the upper base of the testing machine pulls the middle plate upward, causing the specimen to undergo shear deformation; Result calculation: Based on the dimensions of the specimen, the real-time data from the transverse sensor and the sensors on the testing machine, and combined with the shear strain ε, shear stress σ, and transverse stress... The calculation formula yields the shear strain ε, shear stress σ, and transverse stress corresponding to the specimen. ; The formula for calculating shear strain ε is: ， in This represents the vertical change. The initial thickness of the test block; The formula for calculating shear stress σ is: ， in For longitudinal force, W is the initial length of the test block, and W is the initial width of the test block; Transverse stress The calculation formula is: ， in It is a lateral force. is the initial length of the test block, and w is the initial width of the test block.

2. The method for testing large strain shear of low-modulus foamed elastic materials according to claim 1, characterized in that, The specific process of sample preparation is as follows: First, measure the dimensions of the test block and check its quality. The length of the test block should be 25±1mm, the width should be 14±1mm, and the thickness should be 14±1mm. The test block should be free of rubber skin and have a smooth, defect-free surface. The parallelism and flatness tolerances between the two bonding surfaces of the test block should not exceed 0.5mm. Then, the bonding surfaces of the middle plate and side plates are roughened by sandblasting to increase the bonding strength with the adhesive. Next: Mark the bonding positions of the test blocks on the side plates and the middle plate respectively; Finally, apply adhesive to the side of the test block and then attach the test block to the joint between the middle plate and the side plate. Let it cure at room temperature for no less than 24 hours to obtain the test piece.

3. The method for testing large strain shear of low-modulus foamed elastic materials according to claim 2, characterized in that, The adhesive is a cyanoacrylate adhesive.

4. The method for testing large strain shear of low-modulus foamed elastic materials according to claim 1, characterized in that, The shear strain test is conducted at strain levels of 30%, 50%, 70%, 100%, 150%, and 200%. At each strain level, the test piece is cyclically loaded at least 5 times, with a strain rate of 1% / s for each loading.

5. A fixture for testing large strain shear of low-modulus foamed elastic materials, used to implement the method for testing large strain shear of low-modulus foamed elastic materials as described in any one of claims 1 to 4, characterized in that, Includes a base connected to the lower base of the testing machine and a clamp mounted on the base; The fixture includes a left clamping plate and a right clamping plate that are vertically fixed to the base by bolts, a transverse sensor is fixed on the right clamping plate, a sensor transition plate is fixed on the transverse sensor, the test piece is clamped between the left clamping plate and the sensor transition plate, one side plate is positioned on the left clamping plate, and the other side plate is positioned on the sensor transition plate.

6. The high-strain shear testing fixture for low-modulus foamed elastic materials according to claim 5, characterized in that, The top of the middle plate is higher than the side plate and has a connection hole. The connection hole is connected to the upper base of the testing machine through a pin. A transition joint is fixed on the bottom surface of the base along the vertical direction. The transition joint is connected to the lower base of the testing machine through a pin.

7. The high-strain shear testing fixture for low-modulus foamed elastic materials according to claim 6, characterized in that, The base and the left and right clamps form a guiding fit, and a strip-shaped through hole is opened on the base. The left and right clamps are fixed to the base by bolts that extend into the strip-shaped through hole.

8. The high-strain shear testing fixture for low-modulus foamed elastic materials according to claim 5, characterized in that, The lateral sensor is a three-dimensional load sensor.

9. The high-strain shear testing fixture for low-modulus foamed elastic materials according to claim 5, characterized in that, Grooves that mate with the side plates are provided on both the left clamping plate and the sensor transition plate. The side plates are inserted into the grooves. Tightening bolts are installed on the top of both the left clamping plate and the sensor transition plate. The lower end of the tightening bolts is pressed against the top surface of the side plates.

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