A high-coaxiality tensile test fixture and methods of use and applications thereof

Abstract

The present application relates to a kind of high coaxiality tensile test fixture, including two fixture components, fixture component includes fixture body, adapter and positioning pin, positioning pin and adapter fixed connection, fixture body and positioning pin rotation connection;Fixture body is equipped with test chute, pre-pressing piece is equipped in test chute, test chute sliding connection has I-shaped chuck, pre-pressing piece and I-shaped chuck contact;Fixture body is equipped with scale line, scale line is distributed along I-shaped chuck in test chute sliding direction, I-shaped chuck is equipped with pointer cooperation scale line;The I-shaped chuck of two fixture components is directly opposite and is arranged.The present application also relates to a kind of high coaxiality tensile test fixture and its use method and application.The present application has sample and stress coaxiality high, sample is not prone to operating damage, test data is accurate, belongs to material performance test field.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material performance testing, in particular to a tensile test fixture with high coaxiality and a method and application thereof. BACKGROUND

[0002] Tensile test is a test method for determining the mechanical properties of materials, such as elastic modulus, tensile strength, elongation at break and reduction of area, by applying axial tensile load to a tensile specimen. Tensile test is not only applied to check whether the material quality meets the corresponding standards, but also widely used in basic scientific research in the field of materials in colleges and universities and research institutes.

[0003] The national standard GB / T 228.1-2010 makes clear provisions for the size of plate-shaped metal tensile specimen, including: the original width b o of the parallel section of the tensile specimen is limited to 10, 12.5, 15, 20 mm, and the original gauge length L o is preferably taken (S0 refers to the cross-sectional area of the parallel section), and is not less than 15 mm. However, under special research conditions such as powder metallurgy and additive manufacturing, due to factors such as expensive raw materials and limited space in the forming bin, it is difficult to strictly prepare the tensile specimen according to GB / T 228.1-2010. Generally, under the premise of keeping the proportion coefficient 5.65 unchanged, non-standard plate-shaped tensile specimens with smaller size are used for the determination of the mechanical properties of materials.

[0004] Currently, most colleges and research institutions use electronic universal testing machines for tensile test. The matching fixtures of such testing machines are designed and manufactured for standard tensile specimens, and use arrayed convex teeth + self-locking mechanism to prevent specimen loosening, and the clamping pressure is applied by manually rotating the locking handle. Using the matching fixtures of such testing machines for tensile test of non-standard plate-shaped tensile specimens has the following three problems to be solved:

[0005] Firstly, the matching upper and lower fixtures do not have the ability to ensure coaxiality, and whether the tensile specimen is inclined depends entirely on subjective judgment. The coaxiality of the tensile load and the specimen not only depends heavily on the operation ability of the test personnel, but also lacks principle basis for the subjective judgment result.

[0006] Secondly, non-standard plate-shaped tensile specimens are usually small in size and thin in thickness. When the clamping force is improper, the head of the specimen clamping is prone to deformation, and even cracks may occur, becoming the crack source in the subsequent tensile loading process, and the stress-strain curve obtained cannot fully reflect the true mechanical properties of the material.

[0007] Thirdly, the above-mentioned fixture is bulky, and multiple people are needed to cooperate during the installation and disassembly process, which has a high safety risk.

[0008] The coaxiality of the applied tensile load and the tensile sample is a key factor affecting the accuracy of test data. If the tensile load is not applied along the axis of the tensile sample, shear stress will be introduced during deformation, affecting the purity of the material fracture mechanism and causing serious errors in the determination of the tensile mechanical properties of the material. Therefore, the above problems seriously affect the accuracy and process safety of the results of non-standard sample tensile tests, and the demand for fixtures suitable for non-standard sample tensile tests is urgent. Depending on the focus of the problem, existing non-standard plate-shaped tensile sample fixtures can be divided into two categories.

[0009] The first type of fixture aims to improve coaxiality. The main feature of the tensile sample fixture disclosed in the granted patents CN 213957001 U and CN 205593843 U is that the tensile load is applied along the axis of the fixture by fitting the test sample clamping head to the arc-shaped transition section between the non-standard plate-shaped tensile sample clamping head and the parallel section, which can make the tensile sample coaxial with the fixture. The main disadvantages are: first, in the case of significant assembly gap between the sample and the test slide, or significant processing error of the sample clamping head, it is impossible to determine whether the sample is inclined in the test slide; second, it can only roughly determine whether the sample clamping head is coaxial with the fixture, but it does not have the ability to ensure the coaxiality of the upper and lower fixtures.

[0010] The second type of fixture addresses the problem of improper clamping force. The utility model patent with the granted patent number CN 206546295 U provides a non-standard tensile sample fixture, which mainly features clamping the upper and lower heads of the plate-shaped tensile sample with main and auxiliary clamping plates with serrations, and applying clamping force through tightening screws to prevent the plate-shaped tensile sample from loosening. The main disadvantage is that this type of fixture can only reduce the clamping pressure, but it does not have the ability to ensure the coaxiality of the tensile load and the plate-shaped tensile sample, and the sample may still be clamped obliquely.

[0011] The application number 202211210887.8 provides a high-precision dog bone test piece uniaxial tensile test device and test method, which mainly features mounting the sample in the test slide of the fixture and clamping the upper and lower clamping plates in the parallel section of the sample to fix the displacement meter for strain calculation and the level meter for judging coaxiality, to ensure the coaxiality of the upper and lower fixtures. The main disadvantage is that non-standard plate-shaped tensile samples are usually small in size, with a parallel section of less than 20 mm, and there is not enough space to add the upper and lower clamping plates and the displacement meter and level meter, making this solution not feasible for implementation under research conditions.

[0012] In summary, if a high-coaxiality tensile test fixture can be invented, which can simultaneously ensure the coaxiality of the sample and the fixture, the coaxiality of the upper and lower fixtures, and has the advantages of compact structure, flexibility, and lightness, it will make up for the shortcomings of the existing test machine fixtures and improvement solutions, and help to improve the accuracy and process safety of non-standard sample tensile test results. SUMMARY

[0013] In view of the technical problems existing in the prior art, the present application aims to provide a high-coaxiality tensile test fixture to solve the problem that the prior tensile test fixture is difficult to ensure high coaxiality between the upper and lower fixtures and between the fixture and the tensile test sample, and is prone to introduce shear stress in the tensile test process to cause the tensile test sample to break prematurely and affect the determination of the mechanical property index.

[0014] The second object of the present application is to provide a use method of the high-coaxiality tensile test fixture to solve the problem that the prior test machine supporting fixture is bulky and is prone to damage the test sample when clamping, and is difficult to be applied to small-size non-standard plate-shaped tensile test samples.

[0015] The third object of the present application is to provide an application of the high-coaxiality tensile test fixture to solve the problem that the non-standard plate-shaped tensile test sample usually has a small size and a thin thickness, and when the clamping force is improper, the test sample clamping head is prone to deformation, even to crack to become a crack source in the subsequent tensile loading process, and the obtained stress-strain curve cannot fully reflect the real mechanical property index of the material.

[0016] In order to achieve the above objects, the present application adopts the following technical solutions:

[0017] A high-coaxiality tensile test fixture comprises two fixture assemblies, each fixture assembly comprising a fixture main body, an adapter and a positioning pin, the positioning pin and the adapter being fixedly connected, and the fixture main body and the positioning pin being rotationally connected; the fixture main body is provided with a test sliding groove, the test sliding groove is provided with a pre-pressing piece, and the test sliding groove is slidably connected with an I-shaped chuck, the pre-pressing piece is in contact with the I-shaped chuck; the fixture main body is provided with a scale line, the scale line is distributed along the sliding direction of the I-shaped chuck in the test sliding groove, and the I-shaped chuck is provided with a pointer matched with the scale line; the I-shaped chucks of the two fixture assemblies are oppositely arranged.

[0018] As a preferred embodiment, the I-shaped chuck comprises a T-shaped slider, a gasket and a screw, the T-shaped slider is slidably connected with the test sliding groove, the pointer is arranged on the T-shaped slider, the bottom of the T-shaped slider is provided with an inwardly recessed limiting groove, the test sliding groove is recessed inwardly at the bottom of the fixture main body, and the extending direction of the limiting groove is consistent with the extending direction of the test sliding groove; one end of the T-shaped slider is provided with a connecting hole, the gasket is provided with a screw through hole, and the screw is connected with the connecting hole through the screw through hole; the limiting grooves of the two I-shaped chucks are oppositely arranged; and the pre-pressing piece is in contact with the T-shaped slider.

[0019] As a preferred embodiment, the test sliding groove is a rectangular groove recessed from the bottom to the top of the fixture main body, and the edge of the test sliding groove flush with the bottom of the fixture main body is provided with a limiting block.

[0020] As a kind of preferred, the number of limiting block is two, one end of two limiting blocks is fixedly connected with the two inner side walls of test sliding groove respectively, and the other end of two limiting blocks is aligned, and the distance between the other end of two limiting blocks is less than the width of T-shaped slider.

[0021] As a kind of preferred, two limiting blocks are provided with arc transition section matched with tensile sample.

[0022] As a kind of preferred, the side surface of test sliding groove is provided with parallel calibration groove, and the gasket is provided with parallel calibration protrusion, and the parallel calibration protrusion and parallel calibration groove are slidably connected.

[0023] As a kind of preferred, the pre-pressing piece includes spring seat and spring, the spring seat is fixedly connected with test sliding groove, one end of spring is fixedly connected with spring seat, the other end of spring is in contact with the top of T-shaped slider, and the extension direction of spring is consistent with the sliding direction of T-shaped slider in test sliding groove.

[0024] As a kind of preferred, the width of limiting groove is 1-2mm.

[0025] A method for using a tensile test fixture with high coaxiality, using a tensile test fixture, comprising the following steps: S1: cleaning the plate-shaped tensile sample and the tensile test fixture, the cleaning method comprising polishing the sample surface to bright with sandpaper, removing bumps and indentations, and using alcohol to clean each part of the two fixture assemblies to remove dirt; S2: sliding the I-shaped chuck along the test sliding groove, so that the distance between the limiting groove and the test sliding groove is sufficient to accommodate the head of the plate-shaped tensile sample, and the head of the plate-shaped tensile sample is inserted into the limiting groove; S3: control the spring to release slowly until the arc transition section of the plate-shaped tensile sample is in full contact with the arc transition section of the limiting block, and the reading of the pointer and the scale line is equal to the length of the head of the plate-shaped tensile sample; S4: using the same steps as S1-S3, the other head of the plate-shaped tensile sample is loaded into the fixture body to form a fixture-sample assembly; S5: using the positioning pin provided with the tensile testing machine and the adapter to cooperate with the upper and lower top rods of the tensile testing machine, controlling the upward or downward movement of the upper top rod of the tensile testing machine, and leaving a space between the two adapters for the fixture-sample assembly to cooperate with the positioning pin and the adapter; S6: suspending a plumb line from the parallel calibration groove of the fixture assembly connected with the upper top rod, so that the parallel calibration groove of the fixture assembly connected with the lower top rod is flush with the plumb line, to ensure the coaxiality of the two fixture assemblies; S7: starting the tensile testing machine, and outputting the stress-strain curve of the plate-shaped tensile sample.

[0026] The application of a high-coaxiality tensile test fixture, the tensile test fixture is applied to tensile test of metal and ceramic plate-shaped tensile samples, the original gauge length Lo of the metal or ceramic plate-shaped tensile sample is 8-16 mm, the original width bo of the parallel section of the metal or ceramic plate-shaped tensile sample is 2-4 mm, the thickness ao of the metal or ceramic plate-shaped tensile sample is 1-2 mm, and the following formula is satisfied In the formula, So is the cross-sectional area of the parallel section of the metal or ceramic plate-shaped tensile sample, i.e. So = ao x bo.

[0027] The principle of the present application is as follows:

[0028] (1) The present application applies pressure to the I-shaped chuck through the spring fixedly connected to the frame, so as to drive the arc-shaped transition section of the non-standard plate-shaped tensile sample in the limiting groove to tightly adhere to the arc-shaped transition section of the limiting block. The reading of the pointer corresponding to the scale line shows the distance from the bottom surface of the limiting groove to the bottom surface of the test sliding groove. When the measured value indicated by the pointer is consistent with the length of the clamping head of the non-standard plate-shaped tensile sample, it can be judged that the sample is clamped without inclination, and the coaxiality of the relative fixture is good.

[0029] (2) The present application is based on the principle of plumb line, and the plumb line is hung to compare the parallel calibration grooves of the two fixture assemblies. When the plumb line is parallel to the parallel calibration grooves of the two fixture assemblies at the same time, it can be ensured that the coaxiality of the two fixture assemblies is good.

[0030] (3) Under the synergistic action of the coaxial principles (1) and (2), the present application ensures that the tensile load applied in the test is highly coaxial with the height of the non-standard plate-shaped tensile sample, so as to avoid the generation of shear stress and ensure the singleness of the force direction of the tensile sample.

[0031] Overall, the present application has the following advantages:

[0032] (1) The tensile test fixture of the present application overcomes the deficiency that the existing tensile testing machine supporting fixture cannot ensure the coaxiality of the tensile load and the plate-shaped tensile sample. Under the synergistic action of the double coaxial principles described above, the coaxiality of the tensile load and the sample height is effectively ensured, the problem of early fracture of the tensile sample caused by the introduction of shear stress during the tensile test is avoided, and thus the mechanical property indexes of the plate-shaped tensile sample can be accurately measured.

[0033] (2) The present application overcomes the deficiency that the supporting fixture of the testing machine applies excessive clamping force to the plate-shaped tensile sample, which may damage the tensile sample and affect the accuracy of the test data. The tensile sample is fixed by the test sliding groove and the limiting groove, and the possibility of early fracture of the tensile sample near the clamping head is reduced.

[0034] (3) The high-coaxiality tensile test fixture provided by the present application is small and light, the method of use is simple and easy to operate, and a single person can complete the assembly work, which can improve the experimental efficiency of the tensile test.

[0035] (4) The tensile test clamp of the present application realizes the tensile test on the metal and ceramic plate-shaped tensile test sample, solves the problem that the non-standard plate-shaped tensile test sample is usually small in size and thin in thickness, the sample clamping head is easy to deform when the clamping force is improper, even cracks are generated in advance to become the crack source in the subsequent tensile loading process, and the stress-strain curve obtained cannot fully reflect the real mechanical performance index of the material. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is a structure schematic diagram and longitudinal section view of the tensile test clamp with high coaxiality in the tensile test process.

[0037] Figure 2 It is a structure schematic diagram of the clamp assembly.

[0038] Figure 3 It is a shape, structure and calibration slot position diagram of the I-shaped clamp head.

[0039] Figure 4 It is a size schematic diagram of the non-standard plate-shaped tensile test sample used in example 1.

[0040] Figure 5 It is a schematic diagram of the relative position of the sample and the clamp body when example 1 proceeds to step S2.

[0041] Figure 6 It is a schematic diagram of the sample-clamp assembly obtained when example 1 proceeds to step S4.

[0042] Figure 7 It is a schematic diagram of the process of inserting the positioning pin when example 1 proceeds to step S5.

[0043] Figure 8 It is a schematic diagram of comparing the parallel calibration slot with the suspended plumb line when example 1 proceeds to step S6.

[0044] Figure 9 It is a stress-strain curve obtained by 9 times of cyclic loading until the sample is broken in example 1.

[0045] Figure 10 It is a comparison diagram of the non-standard plate-shaped tensile test sample before and after the tensile test.

[0046] Figure 11 It is a comparison diagram of the non-standard plate-shaped tensile test sample before and after the comparative example.

[0047] Among them, 1 is the clamp assembly, 2 is the positioning pin of the tensile testing machine, 3 is the upper push rod, 4 is the lower push rod, 11 is the clamp body, 12 is the connector, 13 is the positioning pin, 111 is the frame, 112 is the I-shaped chuck, 113 is the spring, 114 is the spring seat, 115 is the test slide, 116 is the limiting groove, 117 is the T-shaped slider, 118 is the washer, 119 is the screw, 1110 is the pointer, 5 is the plate tensile specimen, 1111 is the parallel calibration protrusion, 1112 is the scale line, and 6 is the plumb line. Detailed Implementation

[0048] The present invention will now be described in further detail with reference to specific embodiments.

[0049] Example 1:

[0050] This embodiment provides a high coaxiality tensile testing fixture. Based on the principle of plumb line, the fixture ensures the coaxiality of the two fixture components while simultaneously ensuring the coaxiality of the clamped plate-shaped specimen relative to the fixture through pre-compression of the I-shaped chuck by spring end rings. Under the synergistic effect of these two mechanisms, a high degree of coaxiality between the applied tensile force and the plate-shaped tensile specimen is guaranteed.

[0051] like Figure 1 As shown, the high coaxiality tensile test fixture includes two high-strength steel fixture assemblies 1 arranged coaxially. The fixture assembly 1 consists of a fixture body 11, a connector 12 and a positioning pin 13.

[0052] The fixture body 11 includes a frame 111, an I-shaped chuck 112, a spring 113, and a spring seat 114. The I-shaped chuck 112 is installed into a groove in the frame. One end of the spring 113 is fixedly connected to the spring seat 114, and the other end is pre-pressed against the top surface of the I-shaped chuck 112. The spring seat 114 is connected to the frame 111 via a threaded connection. In this embodiment, it is preferable that one end of the spring 113 is brazed to the spring seat 114.

[0053] Connector 12 connects the fixture body 11 to the tensile testing machine. Connector 12 and fixture body 11 are engaged via positioning pin 13. Connector 12 is also engaged with the upper and lower push rods (3, 4) of the tensile testing machine. In this embodiment, the test is preferably carried out on a UTM5205 type electronic universal testing machine.

[0054] like Figure 1 , 2 As shown, the arc-shaped transition section of the limiting block in the test groove 115 of the frame 11 fits the arc-shaped transition section of the plate-shaped tensile specimen 5; the middle part of the I-shaped clamp 112 is a limiting groove 116 that conforms to the thickness of the plate-shaped tensile specimen 5. In this embodiment, the limiting block and the frame 11 are integrally formed, and the limiting block is directly cut out of the frame by wire cutting.

[0055] like Figure 2 ,3 As shown, the I-shaped chuck 112 consists of a T-shaped slider 117 and a washer 118, which are connected by screws 119. The side of the T-shaped slider 117 is engraved with a pointer 1110. In this embodiment, the height of the pointer 1110 is preferably flush with the bottom surface of the limiting groove 116, which is used to indicate the position of the end of the clamping head of the plate-shaped tensile specimen 5. The side of the washer 118 is engraved with two parallel calibration grooves 1111 to check the coaxiality of the two clamping bodies.

[0056] Figure 2 The scale line 1112 on the side of the middle frame 111 is aligned with the pointer 1110 of the T-shaped slider so that the measured length value is consistent with the length of the clamping head of the plate tensile specimen 5, thus ensuring that the plate tensile specimen 5 is coaxial with the two clamp bodies 11.

[0057] The I-shaped clamp has a limiting groove width of 1-2 mm to accommodate plate tensile specimens of various sizes. In this embodiment, 1.5 mm is preferred to reliably clamp the non-standard plate tensile specimens made of NiTi alloy as described below.

[0058] To test 4D printing Ni 49.4 Ti 50.6 The room-temperature superelasticity of shape memory alloys was demonstrated by cyclic tensile testing using the high coaxiality tensile testing fixture provided in this invention. The alloy was fabricated with a total length of 32 mm, a parallel section length of 16 mm, and a parallel section cross-section of 3 × 1.5 mm. 2 Non-standard plate tensile specimens, such as Figure 4 As shown, the gauge length is taken according to GB / T 228.1. The experiment includes the following steps:

[0059] S1: Clean the plate tensile specimen and tensile test fixture. The cleaning method includes sanding the surface of the specimen with sandpaper until it is shiny, removing bumps and dents, and wiping each part of the two fixture components with alcohol to remove dirt.

[0060] S2: Slide the I-shaped clamp along the test groove until the distance between the limiting groove and the test groove is sufficient to accommodate the clamping head of the plate tensile specimen, and insert the clamping head of the plate tensile specimen into the limiting groove; Figure 5 As shown;

[0061] S3: Control the spring to release slowly until the arc transition section of the plate tensile specimen is in complete contact with the arc transition section of the limiting block. Compare the pointer and scale readings. In this embodiment, the reading is 5.2 mm, which is consistent with the length of the clamping head of the plate tensile specimen.

[0062] S4: Using the exact same steps as S1-S3, insert the other clamping head of the plate-shaped tensile specimen into the fixture body to form a fixture-status assembly, as shown below. Figure 6The embodiment in step S4 reads the value equal to step S3, indicating that the coaxiality of the sample relative to the fixture is good at this time;

[0063] S5: The positioning pin 2 of the tensile testing machine is used to cooperate with the adapter and the upper and lower top rods of the tensile testing machine. The upstroke or downstroke of the upper top rod of the tensile testing machine is controlled, and enough space is left between the two adapters for the fixture-sample assembly to cooperate with the positioning pin and the adapter, as shown in Figure 7 The material of the positioning pin of the tensile testing machine is the same as that of the fixture body, which is made of high-strength steel. Its original function is to connect the upper and lower top rods of the tensile testing machine and the matching fixture, and now it is used to connect the upper and lower top rods of the tensile testing machine and the adapter;

[0064] S6: The plumb line is hung from the parallel calibration groove of the fixture assembly connected to the upper top rod, so that the parallel calibration groove of the fixture assembly connected to the lower top rod is flush with the plumb line, to ensure the coaxiality of the two fixtures; as shown in Figure 8 The plumb line hung in the embodiment is flush with the calibration grooves of the two fixtures;

[0065] S7: Start the tensile testing machine to output the cyclic stress-strain curve of the sample. The 9-cycle stress-strain curve of the non-standard plate-shaped tensile sample of Ni 49.4 Ti 50.6 alloy until fracture is shown in Figure 9 The measured super-elastic Ni 49.4 Ti 50.6 alloy has a tensile strength of 604 MPa after 8 cycles. This data meets and far exceeds the requirements of GB / T24627-2009 for the mechanical properties of nickel-titanium shape memory alloys, specifically the tensile strength ≥551 MPa.

[0066] As shown in Figure 10 To obtain accurate strain values, the embodiment hangs an extensometer in the gauge length interval of the non-standard plate-shaped tensile sample between steps S6 and S7. The blade opening distance of the extensometer is 12 mm, the post-breakage crack is located within the gauge length interval, the fracture is flat and perpendicular to the sample axis, indicating that the tensile stress is coaxial with the sample height.

[0067] The application of the tensile testing fixture with high coaxiality used in this embodiment is equally applicable to various non-standard size metal and ceramic plate-shaped tensile samples. The original gauge length L o = 8-16 mm, the original width b o of the parallel section = 2-4 mm, the thickness a o = 1-2 mm, and satisfy The formula S o is the cross-sectional area of the parallel section of the plate-shaped tensile sample, that is, S o = a o × b o .

[0068] Embodiment 2:

[0069] The high coaxiality tensile test fixture provided by the embodiment ensures the coaxiality of two fixture assemblies based on the principle of perpendicular line, and ensures the coaxiality of the clamped plate-shaped sample relative to the fixture through the pre-pressing of the spring end ring on the I-shaped chuck. Under the synergistic effect of the above double mechanisms, the high coaxiality of the applied tension and the plate-shaped tensile sample is ensured.

[0070] As shown in Figure 1 , the high coaxiality tensile test fixture comprises two high-strength steel fixture assemblies 1 arranged coaxially, and each fixture assembly 1 comprises a fixture body 11, a connector 12 and a positioning pin 13.

[0071] The fixture body 11 comprises a frame 111, an I-shaped chuck 112, a spring 113 and a spring seat 114; the I-shaped chuck 112 is installed into the frame sliding groove; one end of the spring 113 is fixedly connected to the spring seat 114, and the other end is pre-pressed on the top surface of the I-shaped chuck 112; and the spring seat 114 is connected to the frame 111 through threaded cooperation. In the embodiment, the one end of the spring 113 is preferably fixedly connected to the spring seat 114 by brazing.

[0072] The connector 12 connects the fixture body 11 and the tensile testing machine, the connector 12 is matched with the fixture body 11 through the positioning pin 13, and the connector 12 is matched with the upper and lower top rods (3, 4) of the tensile testing machine. In the embodiment, the test is preferably carried out on a UTM5205 type electronic universal testing machine.

[0073] As shown in Figure 1 , 2 , the arc-shaped transition section of the limiting block in the test sliding groove 115 of the frame 11 is matched with the arc-shaped transition section of the plate-shaped tensile sample 5; and the middle part of the I-shaped chuck 112 is a limiting groove 116 conforming to the thickness of the plate-shaped tensile sample 5.

[0074] As shown in Figure 2 , 3 , the I-shaped chuck 112 is composed of a T-shaped sliding block 117 and a gasket 118, the T-shaped sliding block 117 and the gasket 118 are connected by a screw 119, the side surface of the T-shaped sliding block 117 is marked with a pointer 1110, and the height of the pointer 1110 is preferably flush with the bottom surface of the limiting groove 116, which is used to indicate the position of the end of the clamped head of the plate-shaped tensile sample 5; and the side surface of the gasket 118 is marked with two parallel calibration grooves 1111, which are used to check the coaxiality of the two fixture bodies.

[0075] Figure 2 The scale line 1112 on the side surface of the middle frame 111 is matched with the pointer 1110 of the T-shaped sliding block, so that the measured length value is consistent with the length of the clamped head of the plate-shaped tensile sample 5, and then the coaxiality of the plate-shaped tensile sample 5 and the two fixture bodies 11 can be ensured.

[0076] The limiting groove of the I-shaped chuck is 1-2 mm wide, so as to accommodate various sizes of plate-shaped tensile samples. In this embodiment, the width is preferably 2 mm, so as to reliably clamp the non-standard plate-shaped tensile sample of ZrO2 ceramic described below.

[0077] To test the tensile strength of ZrO2 ceramic prepared by SPS (spark plasma sintering), a high-coaxiality tensile test fixture is used for tensile test. The ceramic sample is prepared into a non-standard plate-shaped tensile sample with a total length of 40 mm, a parallel section length of 15 mm, and a parallel section cross section of 3x2 mm 2 , and a gauge length of 13 mm according to GB / T 23805. The test includes the following steps:

[0078] S1: clean the plate-shaped tensile sample and the tensile test fixture, the cleaning method including polishing the sample surface to a bright finish using sandpaper to remove bumps and dents, and using alcohol to clean each part of the two fixture assemblies to remove dirt;

[0079] S2: slide the I-shaped chuck along the test sliding groove, so that the distance between the limiting groove and the test sliding groove is sufficient to accommodate the plate-shaped tensile sample clamping head, and insert the plate-shaped tensile sample clamping head into the limiting groove;

[0080] S3: control the spring to slowly release until the arc-shaped transition section of the plate-shaped tensile sample is in full contact with the arc-shaped transition section of the limiting block, and read the value of the pointer and the scale, which in this embodiment is 5.5 mm, consistent with the length of the plate-shaped tensile sample clamping head;

[0081] S4: using the same steps as S1-S3, the other clamping head of the plate-shaped tensile sample is loaded into the fixture body to form a fixture-sample assembly. In this embodiment, the reading value at step S4 is equal to that at step S3, indicating that the sample is in good coaxiality with the fixture at this time;

[0082] S5: use the positioning pin 2 provided with the tensile testing machine to cooperate with the adapters and the upper and lower top rods of the tensile testing machine, control the upward or downward movement of the upper top rod of the tensile testing machine, and leave enough space between the two adapters for the fixture-sample assembly to cooperate with the positioning pin and the adapter;

[0083] S6: suspend a plumb line from the parallel calibration groove of the fixture assembly connected to the upper top rod, so that the parallel calibration groove of the fixture assembly connected to the lower top rod is flush with the plumb line, so as to ensure the coaxiality of the two fixtures; in this embodiment, the plumb line is flush with the parallel calibration grooves of the two fixture assemblies;

[0084] S7: start the tensile testing machine, and output the cyclic stress-strain curve of the sample. The tensile stress-strain curve of the ZrO2 ceramic prepared into a non-standard plate-shaped tensile sample is obtained.

[0085] In order to obtain accurate strain values, the extensometer is hung on the side of the non-standard plate-shaped tensile specimen between steps S6 and S7, and the opening distance of the extensometer blade is 13 mm.

[0086] Through the above process, the ZrO2 ceramic non-standard plate-shaped tensile specimen is successfully broken in the gauge length interval near the middle position of the specimen, and the fracture is basically perpendicular to the specimen axis, indicating that the applied tensile load is coaxial with the specimen height. The data obtained by the test can represent the mechanical properties of ZrO2 ceramic, and the fracture morphology can reliably reflect the tensile fracture mechanism of ZrO2.

[0087] Comparative Example 1:

[0088] In order to compare the difference in tensile stress coaxiality between the tensile test fixture provided by the application and the fixture matched with the testing machine, the 4D printed Ni 49.4 Ti 50.6 shape memory alloy was subjected to cyclic tensile test using the fixture matched with the testing machine. The loading-unloading procedure was exactly the same as that of Example 1, i.e. unloading when the total strain reached 3%, and reloading when the stress decreased to 0, as shown in the following table. Figure 9 The alloy was made into a non-standard plate-shaped tensile specimen with a total length of 32 mm, a parallel section length of 16 mm, and a parallel section cross section of 3x1 mm 2 , and the gauge length was taken according to GB / T228.1 The comparative test included the following steps:

[0089] S1: clean the plate-shaped tensile specimen and the fixture matched with the testing machine, and the cleaning method includes polishing the surface of the specimen to bright with sandpaper, removing bumps and dents, and removing dirt with alcohol;

[0090] S2: tighten the upper handle of the matched fixture, and sufficiently apply clamping pressure to the upper clamping head of the non-standard plate-shaped tensile specimen of Ni 49.4 Ti 50.6 shape memory alloy;

[0091] S3: start the "fast up" or "fast down" function of the tensile testing machine, and make the lower clamping head of the specimen extend into the lower matched fixture by an appropriate length. Apply clamping pressure to the lower clamping head of the specimen in the same way as step S2;

[0092] S4: start the tensile testing machine, and output the cyclic loading stress-strain curve of the Ni 49.4 Ti 50.6 specimen. After the end of the first loading-unloading cycle, the specimen fractured during the second loading cycle, and the tensile strength measured was only 473 MPa, which failed to meet the mechanical property requirements proposed in GB / T24627-2009.

[0093] The post-fracture specimen morphology is shown in the following figure: Figure 11The fracture is located at the edge of the gauge length interval, close to the arc transition section. Combined with the phenomena of too few cycles and too low tensile strength, it is considered that the clamping pressure of the matching fixture is too large, which causes the operation damage near the head of the specimen. The fracture is obviously not perpendicular to the axis of the tensile specimen, indicating that the applied tensile stress is not coaxial with the tensile specimen. In summary, the matching fixture of the tensile testing machine is not suitable for the Ni 49.4 Ti 50.6 The test results of non-standard plate-shaped tensile specimens are not sufficient to measure the mechanical properties of Ni 49.4 Ti 50.6 The fracture morphology cannot reflect the cyclic tensile fracture mechanism of Ni 49.4 Ti 50.6 .

[0094] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A high-coaxiality tensile test fixture, characterized by: The two clamp assemblies are oppositely arranged, and each clamp assembly comprises a clamp body, an adapter and a positioning pin, the positioning pin and the adapter are fixedly connected, and the clamp body and the positioning pin are rotationally connected. The T-shaped slider is slidably connected with the test sliding groove, the pointer is arranged on the T-shaped slider, the bottom of the T-shaped slider is provided with an inwardly recessed limiting groove, the test sliding groove is recessed from the bottom to the top of the frame, the extending direction of the limiting groove is consistent with the extending direction of the test sliding groove, and the plate-shaped tensile specimen clamping head is inserted into the limiting groove. The one end of the T-shaped slider is provided with a connecting hole, the gasket is provided with a screw through hole, and the screw is connected with the connecting hole through the screw through hole. The limiting grooves of the T-shaped sliders of the two clamp assemblies are oppositely arranged.

2. A high-coaxality tensile test fixture according to claim 1, characterized in that: The pointer height is flush with the bottom surface of the limiting groove, and is used for indicating the position of the plate-shaped tensile specimen clamping head end.

3. A high-coaxality tensile test fixture according to claim 2, wherein: The two parallel calibration grooves are marked on the side surface of the gasket.

4. A high-coaxality tensile test fixture according to claim 3, wherein: The parallel calibration grooves of the two clamp assemblies connected with the upper top rod of the tensile testing machine are flush with the plumb line, so that the coaxiality of the two clamp bodies is ensured.

5. A high-coaxality tensile test fixture according to claim 1, wherein: The scale line on the side surface of the frame is opposite to the pointer of the T-shaped slider, so that the measured length value is consistent with the length of the plate-shaped tensile specimen clamping head, and the coaxiality of the plate-shaped tensile specimen and the two clamp bodies is ensured.

6. A high-coaxality tensile test fixture according to claim 1, wherein: The limiting blocks are arranged on the edges of the test sliding groove flush with the bottom of the clamp body.

7. A method of using a high-coaxiality tensile test fixture according to any one of claims 1-6, characterized in that, The two limiting blocks are oppositely arranged, and the distance between the other ends of the two limiting blocks is less than the width of the T-shaped slider. The two limiting blocks are provided with arc transition sections matched with the plate-shaped tensile specimen. The pre-pressing piece comprises a spring seat and a spring, the spring seat is fixedly connected with the test sliding groove, one end of the spring is fixedly connected with the spring seat, the other end of the spring is in contact with the top of the T-shaped slider, and the extension direction of the spring is consistent with the sliding direction of the T-shaped slider in the test sliding groove. The width of the limiting groove is 1-2 mm. The method comprises the following steps: S1: cleaning the plate-shaped tensile specimen and the tensile testing clamp, the cleaning method comprising polishing the specimen surface to be bright using sandpaper, removing convex points and indentations, and cleaning each part of the two clamp assemblies using alcohol to remove dirt; S2: sliding the T-shaped slider along the test sliding groove to make the distance between the limiting groove and the test sliding groove sufficient to accommodate the plate-shaped tensile specimen clamping head, and inserting the plate-shaped tensile specimen clamping head into the limiting groove; S3: controlling the spring to slowly release until the arc transition section of the plate-shaped tensile specimen is in full contact with the arc transition section of the limiting block, and reading the scale value by comparing the pointer and the scale line, so that the reading value is equal to the length of the plate-shaped tensile specimen clamping head. S4: using the same steps as S1-S3, the other clamping head of the plate-shaped tensile specimen is installed into the fixture body to form a fixture-specimen assembly; S5: using the positioning pin of the tensile testing machine and the adapter and the upper and lower top rods of the tensile testing machine, the upward or downward movement of the upper top rod of the tensile testing machine is controlled, and a space is left between the two adapters for the fixture-specimen assembly to cooperate with the positioning pin and the adapter; S6: the plumb line is hung from the parallel calibration groove of the fixture assembly connected with the upper top rod, so that the parallel calibration groove of the fixture assembly connected with the lower top rod is flush with the plumb line, so as to ensure that the two fixture assemblies are coaxial; S7: start the tensile testing machine, and output the stress-strain curve of the plate-shaped tensile specimen.

8. Use of a high-coaxiality tensile test fixture according to any one of claims 1 to 6, characterized in that: The tensile test fixture is applied to tensile test of a metal or ceramic plate-shaped tensile sample, the original gauge length Lo of the metal or ceramic plate-shaped tensile sample is 8-16 mm, the original width bo of the parallel section of the metal or ceramic plate-shaped tensile sample is 2-4 mm, the thickness ao of the metal or ceramic plate-shaped tensile sample is 1-2 mm, and the following formula is satisfied , wherein So is the cross-sectional area of the parallel section of the metal or ceramic plate-shaped tensile sample, i.e., So = ao x bo.

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