A method utilizing SiC f Method for testing the tensile proportional limit of SiC composite materials using a high-throughput testing fixture

Abstract

This invention belongs to the field of material mechanical property testing technology, and relates to a SiC f A high-throughput testing fixture and method for tensile proportional limit of SiC composite materials is presented. For small-sized Y-shaped end specimens, a corresponding fixture is designed to connect multiple specimens end-to-end, and the self-locking mechanism between the specimens and the fixture effectively transfers the testing machine load to the gauge length of each specimen. The tensile stress on each specimen's gauge length is determined through stress analysis, considering the fixture's self-weight. The tensile strain of each specimen is determined based on the average value of strain gauges attached to the front and rear surfaces of the specimen's gauge length during loading. Multiple SiC composites can be tested simultaneously in a single tensile loading operation. f The tensile stress-strain curve of SiC composite specimens is tested to determine the tensile proportional limit and tensile modulus. This greatly improves experimental efficiency and enables the determination of SiC... f High-throughput testing of the tensile proportional limit of SiC composite materials can ensure precise alignment of the specimen with the loading line of the testing machine and eliminate data dispersion sources related to specimen loading.

Description

Technical Field

[0001] This invention belongs to the field of material mechanical property testing technology, and specifically relates to a SiC... f High-throughput testing fixture and method for tensile proportional limit of SiC composite materials. Background Technology

[0002] SiC f / SiC composite materials, by introducing SiC fibers as a reinforcing phase into the SiC matrix, can greatly improve the toughness of SiC ceramic materials and solve the problem of high brittleness inherent in SiC. At the same time, they retain the excellent properties of SiC ceramic materials, such as high temperature wear resistance. They are widely used in aerospace, military, machinery, chemical, and electronic technology fields.

[0003] SiC f The tensile stress-strain curves of SiC composites often exhibit nonlinear characteristics. The inflection point where the curve deviates from linearity corresponds to the initiation of a through-crack in the matrix. Subsequently, due to the propagation of the matrix crack, fiber pull-out, interface slip, fiber breakage, etc., the material stiffness decreases. The stress corresponding to this inflection point is usually called the matrix cracking strength, or the proportional limit stress. For SiC... f For SiC composite materials, the tensile proportional limit is the most important mechanical property data used in design. Structural designs typically use the tensile proportional limit as the maximum usable strength because once the matrix cracks, environmental media can penetrate the material through these cracks, causing severe degradation of the material's properties due to environmental corrosion. Furthermore, research has shown that SiC... f The tensile proportional limit of SiC is directly related to the material's fatigue properties; SiC with a high tensile proportional limit... f SiC has a longer lifespan and a higher fatigue limit, therefore, for SiC... f For SiC composites, the tensile proportional limit is more valuable than the tensile strength data. It serves not only as the basis for determining allowable values ​​in structural design but also as a measure of the performance of SiC. f The mechanical properties of SiC composites are the most important indicator, therefore the tensile proportional limit test is crucial for SiC. f / SiC composite materials are of great significance.

[0004] Since the stretching ratio limit is a measure of SiC f The mechanical properties of SiC composite materials are the most important indicator of their quality, therefore, in SiC f In the development of SiC, the demand for tensile proportional limit testing is increasing. Currently, SiC... fThe tensile proportional limit of SiC composite materials is generally obtained by stretching a standard straight specimen. This method requires a large specimen size, which is problematic for SiC materials that are expensive to produce and have high processing costs. f / SiC composites are not economical, so material researchers currently favor small-sized Y-shaped end specimens. Using such small-sized specimens can greatly shorten sample preparation time, save material costs, and allow for rapid evaluation of the material process improvement effect, thus helping to shorten the material research and development cycle.

[0005] In the prior art, patent CN103018101A, "A fixture for high-temperature tensile testing of ceramic matrix composites," also uses a Y-shaped end specimen. It utilizes the supporting force generated by the contact between the wedge surface at the specimen end and the wedge surface of the Y-shaped tenon groove in the integrated fixture to transfer the load. Patent CN 109813610A, "A combined fixture for ultra-high temperature tensile testing of ceramic matrix composites," also uses a Y-shaped end specimen. The fixture employs a semi-circular truncated bracket with a Y-shaped tenon groove to connect the Y-shaped end specimen to the testing machine. It also utilizes the contact and clamping of the wedge surfaces at both ends of the Y-shaped end specimen with the wedge surfaces of the slot in the fixture to achieve self-locking between the specimen and the fixture. However, both of these patents employ the design concept of machining an integrated Y-shaped tenon groove in the fixture with a depth greater than the specimen thickness. During the test, the specimen is suspended in the Y-shaped tenon groove in the fixture. This makes it difficult to ensure the alignment of the specimen relative to the loading line of the testing machine. In addition, since the two types of fixtures mentioned above rely entirely on the clamping force between the two wedge-shaped surfaces of the specimen and the wedge-shaped surfaces of the fixture to transfer the load, the specimen at the wedge surface often crushes, resulting in unstable load transfer and even test failure.

[0006] Because the load on these small-sized Y-shaped end specimens is relatively small, the influence of external factors such as specimen loading and operator differences is more significant than that on conventional specimen testing. Loading multiple specimens simultaneously in a single loading operation can effectively eliminate these errors. Furthermore, since the small-sized Y-shaped specimens are small in size, and tensile limit testing does not require breaking the specimen, we consider connecting these small-sized Y-shaped specimens end-to-end. For this purpose, a dedicated tooling fixture needs to be designed, and a method for calculating the tensile stress in the specimen at different locations, taking into account the fixture's own weight, needs to be developed, providing a SiC... f A high-throughput test method for the tensile proportional limit of SiC composite materials is proposed, which enables the simultaneous tensile loading of multiple specimens in a single test. Summary of the Invention

[0007] The purpose of this invention is to provide SiC fThis paper presents a high-throughput testing fixture and method for the tensile proportional limit of SiC composite materials. The fixture is designed to connect multiple specimens end-to-end and to the testing machine, enabling simultaneous tensile testing of several specimens under a single loading. A method is also developed to obtain the true tensile stress-strain curves of the gauge length of the Y-shaped end specimens, thus addressing the challenges of SiC tensile proportional limit testing. f High-throughput testing of the tensile proportional limit of SiC composites, eliminating human systematic errors related to specimen loading, and realizing SiC f / SiC tensile proportional limit test efficiency and accuracy are both improved.

[0008] To solve this technical problem, the technical solution of the present invention is as follows:

[0009] On the one hand, a SiC is provided f High-throughput testing fixture for tensile proportional limit of SiC composite materials.

[0010] The high-throughput tensile testing fixture maintains the centering of each specimen under loading conditions, enabling multiple specimens to be connected end to end. During loading, the fixture and specimens are self-locking, effectively transferring the load of the testing machine to the gauge length of each specimen, thus enabling the simultaneous tensile testing of multiple specimens in one mechanical test.

[0011] The high-throughput tensile test fixture is divided into two parts: a part that connects to the testing machine and a part that connects multiple specimens.

[0012] The connection part with the testing machine consists of four T-shaped clamps with trapezoidal grooves machined in the middle. They are used in pairs. The shape of the trapezoidal groove is similar to the shape of the Y-shaped end of the specimen, and the inclined surfaces are consistent. The inclined surfaces of the two can fit together. The upper end of the first Y-shaped end specimen is clamped between the two T-shaped clamps, and the upper part of the Y-shaped end specimen can be precisely locked into the trapezoidal grooves of the two T-shaped clamps. During the test, this pair of T-shaped clamps is clamped in the upper chuck of the testing machine. The other two T-shaped clamps also form a pair, clamping the lower end of the last Y-shaped end specimen in the middle. The lower part of the Y-shaped end specimen can also be precisely locked into the trapezoidal grooves of the two T-shaped clamps. During the test, this pair of T-shaped clamps is clamped in the lower chuck of the testing machine.

[0013] The tooling fixture consists of n pairs of rectangular clamping plates that are combined in pairs. Each rectangular clamping plate has two trapezoidal grooves that are mirror-symmetrically machined at its upper and lower ends, similar to the end configuration of the Y-shaped specimen. The end of the Y-shaped specimen can be precisely locked in these grooves. The lower end of each specimen and the upper end of the specimen adjacent to it are locked into the same pair of rectangular clamping plates in the mirror-symmetrical trapezoidal grooves. The two rectangular clamping plates and the specimen are then fixed and clamped together with bolts.

[0014] In a tensile test, each specimen is suspended in a fixture when under tension. Because the end of the Y-shaped specimen fits the trapezoidal groove in a pair of clamps, the fit between the fixture and the specimen becomes increasingly tight under tensile load, effectively transferring the load. Therefore, the load of the testing machine can be transferred to the gauge length of each specimen through this set of self-locking fixture / test assembly.

[0015] The number n depends on the number of samples to be tested, and n is the number of samples minus 1.

[0016] When the two pairs of T-shaped clamps connected to the testing machine, and the n pairs of rectangular clamps in the middle for connecting multiple specimens end to end, are fully fitted together, the depth of the trapezoidal groove formed in the middle is slightly smaller than the thickness of the specimen (the depth of the trapezoidal groove after fitting is less than the thickness of the specimen). This design can adapt to varying specimen thicknesses, ensuring that the centerline of each specimen always precisely coincides with the loading line of the testing machine, ensuring the centering of the loading state of each specimen, and ensuring that the load is effectively and smoothly transmitted in this loading system.

[0017] The width of the "I-shaped" portion of the two pairs of T-shaped clamps connected to the testing machine is exactly equal to the width of the testing machine's clamping block. When clamping, aligning them with the clamping block will achieve centering of the entire loading system. The ends of the T-shaped clamps have handholds, which are two small rectangles resembling "wings" extending from the left and right ends of the T-shaped clamps and located outside the clamping block. These handholds are designed to facilitate operation by the tester when clamping a pair of T-shaped clamps together into the clamping block.

[0018] Each pair of rectangular clamps is fixed together with bolts; one of the rectangular clamps in each pair has four identical through holes machined at its four corners, with the hole diameter slightly larger than the bolt diameter, so that the bolt can pass through smoothly; the other rectangular clamp that is combined with it has four identical threaded holes machined at its four corners, so that the bolt can be screwed in.

[0019] The clamp is suitable for SiC with a Y-shaped end. f For the testing of the tensile properties of SiC specimens, the specific specimen configuration and dimensions can be determined according to the actual situation.

[0020] The number of test specimens is at least three. During use, the number of test specimens and the number of pairs of rectangular clamps used to connect the intermediate test specimens can be increased or decreased. The maximum number of test specimens that can be tested at one time depends on the stroke of the crossbeam of the testing machine.

[0021] On the other hand, a method utilizing the above-mentioned SiC is provided. fA method for high-throughput testing of the tensile proportional limit of SiC composite materials using a high-throughput testing fixture. This method utilizes the section method to perform stress analysis on the gauge length section of each specimen, calculates the true tensile load on each gauge length section, further plots the tensile stress-strain curve for each specimen, and determines the tensile proportional limit and tensile modulus of each specimen based on the curve. The specific steps are as follows, where steps 1) and 2) do not necessarily have a specific order and can be interchanged:

[0022] 1) Test preparation: Assemble the specimen and fixture according to the neutrality requirements to obtain the specimen / fixture assembly;

[0023] 2) During the test, strain gauges were attached to the center of the front and rear surfaces of each specimen. The readings of the strain gauges attached to the front and rear surfaces of all specimens were monitored during the test. The average value of the strain gauge readings on the front and rear surfaces of each specimen was taken as the tensile strain of the specimen.

[0024] 3) Load the assembly at a constant loading rate until any one of the specimens breaks. During the loading process, record the load on the testing machine and the strain data of the strain gauges attached to the surface of each specimen.

[0025] 4) Based on the tensile stress calculated for each specimen and the tensile strain measured for each specimen, plot the tensile stress-strain curve for each specimen. Determine the tensile proportional limit based on the stress level corresponding to the deviation of the tensile stress-strain curve from the initial linear segment. Calculate the tensile modulus of each specimen based on the slope of the initial linear segment of the stress-strain curve.

[0026] The method is applicable to SiC at room temperature. f Testing of the tensile proportional limit of SiC composite materials.

[0027] The beneficial effects of this invention are:

[0028] 1. The SiC of the present invention f The high-throughput testing fixture for the tensile proportional limit of SiC composite materials can obtain the tensile proportional limit of multiple specimens in a single test, greatly improving testing efficiency.

[0029] 2. The SiC of the present invention f A high-throughput test fixture for the tensile proportional limit of SiC composite materials can eliminate experimental operation errors that may be introduced by testing a set of test samples separately, and reduce possible sources of data dispersion.

[0030] 3. The SiC of the present invention fThe high-throughput test fixture for the tensile proportional limit of SiC composite materials consists of two pairs of T-shaped clamps connected to the testing machine, and several pairs of small rectangular clamps in the middle that form trapezoidal grooves when the specimens are fully fitted together. The depth of these grooves is slightly smaller than the specimen thickness. This design ensures that the centerline of each specimen remains precisely aligned with the loading line of the testing machine when the specimen thickness changes.

[0031] 4. The SiC of the present invention f The high-throughput testing method for the tensile proportional limit of SiC composite materials uses several pairs of split clamps with trapezoidal grooves in the middle to clamp the Y-shaped specimen. The specimen is then tightened by the testing machine chuck or bolts. The load transfer method of the clamp to the Y-shaped specimen includes the contact pressure of the left and right wedge surfaces of the specimen and the friction force at the front and rear surfaces of the specimen. This effectively avoids the problem of the wedge surfaces at both ends of the specimen being crushed when using an integrated wedge groove clamp. Attached Figure Description

[0032] To more clearly illustrate the technical solutions implemented in this invention, the accompanying drawings used in the embodiments of this invention will be briefly explained below. Obviously, the drawings described below are merely some embodiments of this invention. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0033] Figure 1 Schematic diagram of a high-throughput tensile testing fixture;

[0034] Figure 2 The structure of the two pairs of T-shaped clamps and their assembly details with the sample;

[0035] Figure 3 A bottom view of the specimen after a pair of T-shaped clamps have clamped the Y-shaped end of the specimen.

[0036] Figure 4 Front view of the T-shaped clamp;

[0037] Figure 5 A schematic diagram showing how four pairs of rectangular clamps connect multiple samples end to end.

[0038] Figure 6 Detailed structural diagram of a pair of rectangular clamps;

[0039] Figure 7 Top view of the Y-shaped end sample clamped by a pair of rectangular clamps;

[0040] Figure 8 Force analysis diagrams of the five specimens from top to bottom;

[0041] Figure 9 SiC fTensile stress-strain curves of Y-shaped end specimens of SiC composite materials.

[0042] Wherein: 1-A pair of T-shaped clamping plates held in the upper clamping block of the testing machine; 2, 3, 4, 5-The 1st, 2nd, 3rd, and 4th pairs of rectangular clamping plates from top to bottom, used to connect the middle part of the specimen; 6-A pair of T-shaped clamping plates held in the lower clamping block of the testing machine; 7, 8, 9, 10, 100-The 1st, 2nd, 3rd, 4th, and 5th Y-shaped end small specimens from top to bottom; 11, 12-Two separate clamping plates from the pair of T-shaped clamping plates held in the upper clamping block of the testing machine; 61, 62-Clamping... Two separate clamping plates from a pair of T-shaped clamping plates in the lower clamping block of the testing machine: 21, 22 - the first pair from top to bottom, two separate rectangular clamping plates used to connect the middle part of the specimen; 31, 32 - the second pair from top to bottom, two separate rectangular clamping plates used to connect the middle part of the specimen; 41, 42 - the third pair from top to bottom, two separate rectangular clamping plates used to connect the middle part of the specimen; 51, 52 - the fourth pair from top to bottom, two separate rectangular clamping plates used to connect the middle part of the specimen; 110 - The trapezoidal groove in T-shaped clamp 11, 120 - trapezoidal groove in T-shaped clamp 12, 610 - trapezoidal groove in T-shaped clamp 61, 620 - trapezoidal groove in T-shaped clamp 62, 111 - gap formed after a pair of T-shaped clamps and the sample are assembled, 210 - trapezoidal grooves distributed in mirror symmetry in T-shaped clamp 21, 220 - trapezoidal grooves distributed in mirror symmetry in T-shaped clamp 22, 23, 24 - tightening bolts passing through the first pair of rectangular small clamps from top to bottom, 215 - gap formed after the first pair of rectangular small clamps from top to bottom are assembled with the sample, 211, 212, 213, 214 - through holes distributed at the four corners on one of the first pair of rectangular small clamps, 221, 222, 223, 224 - threaded holes distributed at the four corners on the other of the first pair of rectangular small clamps. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The features of various aspects of the embodiments of the present invention will be described in detail below. The present invention will be further described below with reference to the embodiments, specifically the SiC involved in a single loading process in this embodiment. f Five tensile specimens were prepared for the Y-shaped end of the SiC composite material.

[0044] I. Overview

[0045] SiC in this embodiment fA high-throughput testing method for the tensile proportional limit of SiC composite materials includes a fixture for high-throughput tensile testing and a method for determining the true tensile stress-strain curves of the gauge length of specimens at different orientations of the loading system. The high-throughput tensile testing fixture is ingeniously designed to connect multiple specimens end-to-end, and during loading, the self-locking mechanism between the fixture and the specimens effectively transfers the load of the testing machine to the gauge length of each specimen, enabling the simultaneous tensile testing of at least five specimens in a single mechanical test. The tensile stress data processing method considers the influence of the fixture's self-weight, using the section method to perform a detailed stress analysis on the cross-section of each specimen's gauge length, calculating the true tensile load for each specimen's gauge length, and thus determining the tensile stress-strain curve for each specimen. Based on the tensile stress-strain curve, the tensile proportional limit of each specimen is determined.

[0046] This method is applicable to SiC with a Y-shaped end. f The tensile properties of SiC specimens can be tested. Specific specimen configuration and dimensions can be determined based on actual conditions. Furthermore, this method is applicable to SiC specimens grown at room temperature. f The tensile proportional limit test of SiC composites can achieve at least 5 SiC [components] in a single loading. f The testing of SiC tensile specimens can be performed by adding or removing specimens and the number of rectangular clamps used to connect the middle parts of the specimens. The maximum number of specimens that can be tested in one loading depends on the stroke of the testing machine beam.

[0047] II. Fixture Structure for High-Throughput Tensile Testing in this Embodiment

[0048] This embodiment provides a high-throughput tensile testing fixture. Through ingenious design, the fixture connects multiple specimens end-to-end, and during loading, the self-locking mechanism between the fixture and the specimens effectively transfers the machine load to the gauge length of each specimen. This allows for the simultaneous tensile testing of five Y-shaped end specimens in a single mechanical test. The fixture's structure is as follows: Figures 1-7 As shown.

[0049] like Figure 1 As shown, the fixture can be divided into two parts: parts 1 and 6 that connect to the testing machine, and parts 2, 3, 4, and 5 that connect the specimens. Figure 2As shown, the part connected to the testing machine consists of four T-shaped clamps 11, 12, 61, and 62 with trapezoidal grooves machined in the middle. 11 and 12 are used as a pair, and 61 and 62 are used as a pair. A trapezoidal groove 110 with a shape similar to the end shape of the Y-shaped sample is machined at the middle position of one end of the T-shaped clamp 11. A trapezoidal groove 120 with a shape similar to the end shape of the Y-shaped sample is machined at the middle position of one end of the T-shaped clamp 12. A trapezoidal groove 610 with a shape similar to the end shape of the Y-shaped sample is machined at the middle position of one end of the T-shaped clamp 61. A trapezoidal groove 621 with a shape similar to the end shape of the Y-shaped sample is machined at the middle position of one end of the T-shaped clamp 62. The upper part of the first Y-shaped end specimen 7 from top to bottom can be clamped into the trapezoidal grooves 110 and 120 of the two T-shaped clamps 11 and 12. During the test, the upper end of the small Y-shaped end specimen 7 can be clamped between the pair of T-shaped clamps 11 and 12. During the test, this pair of T-shaped clamps 1 is clamped into the upper chuck of the testing machine. The other two T-shaped clamps 61 and 62 also form a pair. The lower end of the last Y-shaped end specimen 100 is clamped into the trapezoidal grooves 610 and 620 of the two T-shaped clamps 61 and 62. During the test, the lower end of the last small Y-shaped end specimen 100 can be clamped into the trapezoidal grooves 610 and 620 of the pair of T-shaped clamps 61 and 62. During the test, this pair of T-shaped clamps 2 is clamped into the lower chuck of the testing machine.

[0050] Furthermore, when the two pairs of T-shaped clamps connected to the testing machine are closed, the depth of the trapezoidal groove formed is slightly smaller than the thickness of the specimen. This design can adapt to varying specimen thicknesses, ensuring that the centerline of each specimen coincides with the loading line of the testing machine, guaranteeing precise alignment of the loading state for each specimen, and facilitating the effective and stable transmission of load within the loading system. Taking a pair of T-shaped clamps 11 and 12 held in the clamping blocks of the testing machine as an example, see... Figure 3 When the upper end of the Y-shaped end sample 7 is clamped in the trapezoidal grooves 110 and 120 of a pair of T-shaped clamps 11 and 12, the thickness of the Y-shaped end sample 7 is slightly greater than the sum of the depths of the two trapezoidal grooves 110 and 120 on the T-shaped clamps 11 and 12. Therefore, the pair of T-shaped clamps 11 and 12 will not fit together, but there will be a small gap 111 between them.

[0051] Furthermore, the width of the "I-shaped" portion 115 of the two pairs of T-shaped clamps held by the testing machine chuck is exactly equal to the width of the testing machine clamping block. Aligning them with the clamping block during clamping ensures the centering of the entire loading system. The two small, wing-like rectangles extending from the left and right ends of the T-shaped clamps, located outside the clamping block, are handheld parts designed for ease of operation by the tester when clamping a pair of joined T-shaped clamps into the clamping block. Taking the first pair of T-shaped clamps as an example, see... Figure 4The width of the "I-shaped" part 115 is exactly equal to the width of the testing machine clamping block, while the two small rectangles 113 and 114 that extend from the left and right ends of the T-shaped clamping plate are the hand-held parts.

[0052] In addition, the fixture enabling high-throughput tensile testing also includes four pairs of identical rectangular clamps for connecting multiple tensile specimens (numbered 2, 3, 4, and 5 from top to bottom). Each pair of rectangular clamps consists of two separate rectangular clamps with a central slot (numbered 21, 22, 31, 32, 41, 42, 51, and 52 from top to bottom and left to right, see...). Figure 5 (See example of the first pair of rectangular clips). Figure 6 Each rectangular clamp 21, 22 has two trapezoidal grooves 210, 220 mirror-symmetrically machined at its upper and lower ends, similar to the end configuration of the Y-shaped specimen. The end of the Y-shaped specimen can be precisely clamped in these grooves. The lower end of the Y-shaped specimen 7 and the upper end of the adjacent Y-shaped specimen 8 are clamped to the same pair of rectangular clamps 21, 22 mirror-symmetrical trapezoidal grooves 210, 220, and the two rectangular clamps and specimens are fixedly clamped with bolts. During the tensile test, each specimen is suspended in the fixture. Because the end of the Y-shaped specimen fits perfectly with the shape of the trapezoidal groove in the fixture, the fit between the fixture and the specimen becomes increasingly tight under tensile load, effectively transferring the load. Therefore, the load of the testing machine can be transferred to the gauge length of each specimen through this set of tensile self-locking clamps / test assembly.

[0053] Furthermore, when the four pairs of rectangular clamps used for connecting the specimens in the middle are put together, the depth of the trapezoidal groove formed is slightly smaller than the thickness of the specimen. This design can accommodate deviations in the thickness of each specimen, ensuring that the centerline of each specimen connected end-to-end coincides with the loading line of the testing machine. This ensures precise alignment of the loading state of each specimen and also facilitates the effective and stable transmission of load within the loading system. Taking the first pair of rectangular clamps 21 and 22 as an example, see... Figure 7 When the lower end of the first Y-shaped end sample 7 is clamped between the first pair of rectangular clamps 21 and 22 and tightened with bolts 23 and 24, the thickness of the Y-shaped end sample 7 is slightly greater than the sum of the depths of the two trapezoidal grooves 210 and 220 of the rectangular clamps 21 and 22. Therefore, the pair of T-shaped clamps 21 and 22 will not fit together, but there will be a small gap 215 between them.

[0054] In addition, the four pairs of rectangular clamps used for connecting the samples in the middle have the same structural features as follows: one of the rectangular clamps has four identical through holes 211, 212, 213, and 214 machined at its four corners, with the hole diameter slightly larger than the bolt diameter so that the bolt can pass through smoothly; the other rectangular clamp has four identical threaded holes 221, 222, 223, and 224 respectively at its four corners so that the bolt can be screwed in.

[0055] III. Determining the true tensile stress-strain curves of the gauge length segment of the specimen at different orientations in the loading system.

[0056] Because the test load is relatively small, the weight of the fixture should not be ignored in order to obtain the true stress in the gauge length of the specimen. Due to the weight of the fixture, the tensile load on the gauge length of the specimen varies at different spatial locations. A detailed stress analysis of each gauge length section can be performed using the classical section method in mechanics of materials to calculate the true tensile load on each gauge length section. The stress analysis of the specimen at each different orientation in the loading system is shown below. Figure 8 .like Figure 8 As shown in (a), the tensile load P1 of the first gauge length segment of the specimen from top to bottom is equal to the testing machine load P; Figure 8 As shown in (b), the tensile load P2 of the second specimen gauge length segment is the testing machine load P minus the weight P of the pair of rectangular clamps above it used to connect the specimen. g ,;like Figure 8 As shown in (c), the tensile load P3 of the third specimen gauge length segment is equal to the testing machine load P minus the weight 2P of the two pairs of rectangular clamps above it used to connect the specimen. g ;like Figure 8 As shown in (d), the tensile load P of the gauge length segment of the fourth specimen n The load P of the testing machine is equal to the weight of the three pairs of rectangular clamps above it used to connect the specimen, 3P. g ;like Figure 8 As shown in (e), the tensile load P of the gauge length segment of the 5th specimen n The load P of the testing machine is equal to the weight of the four pairs of rectangular clamps above it used to connect the specimens, 4P. g The tensile load P borne by each gauge length segment of the specimen. i Divide (i=1,2,3,4,5) by the cross-sectional area of ​​the corresponding gauge length of the specimen to calculate the tensile stress borne by each gauge length segment of the specimen. σ i (i=1,2,3,4,5).

[0057] To obtain the strain of each specimen, strain gauges were attached to the center of the front and rear surfaces of each specimen during testing. The readings of the strain gauges attached to the front and rear surfaces of each specimen were monitored during the test, and the average value of the strain gauge readings on the front and rear surfaces of each specimen was taken as the tensile strain of the specimen. ε i (i=1,2,3,4,5). A set of assembled fixture / test assembly components is loaded at a constant loading rate until any one of the specimens fractures. During the loading process, the load on the testing machine and the strain data of the strain gauges attached to the surface of each specimen are recorded. Based on the recorded data and the dimensions of the specimens, the tensile stress-strain curve of each specimen is determined. The tensile stress-strain curve of each specimen is plotted. The tensile proportional limit of each specimen is determined according to the stress level corresponding to the deviation of the tensile stress-strain curve from the initial linear segment. The tensile modulus is calculated based on the slope of the stress-strain curve of the initial linear segment of each specimen.

[0058] In this embodiment, orthogonally ply SiC f Taking SiC composite material as an example, the tensile proportional limit of a group of 5 specimens at room temperature was tested. The specific operation is as follows:

[0059] 1. The mass m of the pair of rectangular clamps (with four bolts) used to connect the intermediate specimens in the measuring fixture, and the weight of the pair of rectangular clamps are calculated using the following formula: P g =mg.

[0060] 2. Measure the width and thickness of the gauge length segments of the five specimens respectively, and calculate the cross-sectional area of ​​the gauge length segment of each specimen. S i (i=1,2,3,4,5), and strain gauges are attached at the center of the front and rear surfaces of each specimen gauge length segment.

[0061] 3. Using the four pairs of rectangular clamps in the fixture, connect the five specimens end to end. Insert both ends of each specimen into the trapezoidal slot of one of the rectangular clamps in each pair. Then, attach the other clamp in its pair above the specimen, inserting the specimen into its trapezoidal slot as well. Insert the bolts and tighten the specimens and the pair of rectangular clamps. Insert the upper end of the first specimen into a T-shaped clamp, then attach the T-shaped clamp in its pair above the specimen, inserting the specimen into its trapezoidal slot. Then, insert the lower end of the fifth specimen into a T-shaped clamp, then attach the T-shaped clamp in its pair above the specimen. This completes the assembly of the specimens and fixture, resulting in a specimen / fixture assembly.

[0062] 4. The tester holds the two small rectangular parts resembling "wings" that extend from the left and right sides of the T-shaped clamps at the top and bottom ends of the sample / clamp assembly. The uppermost pair of T-shaped clamps are clamped into a pair of wedge-shaped clamps on the upper chuck of the testing machine. At this time, the load on the testing machine is zeroed. Then, the lowermost pair of T-shaped clamps are clamped into a pair of wedge-shaped clamps on the lower chuck of the testing machine.

[0063] 5. Connect a strain gauge to the strain gauge of each specimen, start the testing machine, and load it at a displacement rate of 0.25 mm / min. Continuously collect and record the load of the testing machine and the strain data of the strain gauge attached to the surface of each specimen during the loading process until any one of the specimens breaks.

[0064] 6. Using the continuously recorded load-strain data from the experiment, and considering the weight of the fixture, take each column of load data as the load P1 of the first specimen, and subtract P from each column of load data. g As the load P2 of the second specimen, subtract 2P from each column of load data. g As the load P3 of the third specimen, subtract 3P from each column of load data. g As the load P4 of the fourth specimen, subtract 4P from each column of load data. g The load P5 for the fifth specimen is calculated by dividing the actual load data for each specimen by the cross-sectional area of ​​the gauge length. S i (i=1,2,3,4,5) to obtain the actual stress data of each specimen during loading. σ i (i=1,2,3,4,5). The strain of each specimen is taken as the average value of the strain gauge data attached to its front and rear surfaces. ε i (i=1,2,3,4,5).

[0065] 6. Plot the tensile stress-strain curve for each specimen, such as... Figure 9 As shown, the tensile proportional limit for each specimen was determined based on the stress level corresponding to the deviation of the tensile stress-strain curve from the initial linear segment, and the tensile modulus was calculated based on the slope of the stress-strain curve for each specimen in the initial linear segment. Furthermore, for specimen #3, which fractured among the five specimens, the stress value corresponding to the maximum load was the tensile strength value of specimen #3, and the corresponding strain value was the failure strain of specimen #3. The test results for the five specimens are shown in Table 1.

[0066] Table 1 Summary of Data Results

[0067]

[0068] Experiments have shown that the tensile clamp of the present invention can be well applied to SiC. fThe tensile proportional limit and tensile modulus of the / SiC composite material were tested, and a single value for tensile strength and tensile failure strain was obtained simultaneously. The fixture did not damage the clamping section of the Y-shaped end of the specimen, and the fracture sites of the specimens were all within the gauge length, indicating that the fixture design was reasonable. The data from the five specimens were stable with low dispersion, demonstrating the reliability of the tensile proportional limit testing method of this invention.

[0069] Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

Claims

1. A method utilizing SiC f A method for testing the tensile proportional limit of SiC composite materials using a high-throughput testing fixture, characterized by: The high-throughput tensile testing fixture maintains the centering of each specimen under loading conditions, enabling multiple specimens to be connected end to end. During loading, the fixture and specimens are self-locking, effectively transferring the load of the testing machine to the gauge length of each specimen, thus enabling the simultaneous completion of tensile testing of multiple specimens in a single mechanical test. The high-throughput tensile test fixture is divided into two parts: the part that connects to the testing machine and the part that connects to the specimen. The connection part with the testing machine consists of four T-shaped clamps with trapezoidal grooves machined in the middle. They are used in pairs. The shape of the trapezoidal groove is consistent with the shape of the Y-shaped end of the specimen. The inclined surfaces of the two can fit together. The upper end of the first Y-shaped end specimen is clamped between a pair of T-shaped clamps, and the upper part of the Y-shaped end specimen is locked into the trapezoidal grooves of the two T-shaped clamps. During the test, this pair of T-shaped clamps is clamped in the upper chuck of the testing machine. The other two T-shaped clamps also form a pair, clamping the lower end of the last Y-shaped end specimen in the middle. The lower part of the Y-shaped end specimen is also locked into the trapezoidal grooves of the two T-shaped clamps. During the test, this pair of T-shaped clamps is clamped in the lower chuck of the testing machine. The portion of the clamp connecting the specimens consists of n pairs of rectangular small clamping plates, each rectangular small clamping plate having two trapezoidal grooves machined symmetrically at its upper and lower ends, similar to the end configuration of the Y-shaped end specimen, in which the end of the Y-shaped end specimen is held. The lower end of each sample and the upper end of the sample adjacent to it are clamped into the trapezoidal groove of the same pair of rectangular small clamps, which are mirror-symmetrical, and the two rectangular small clamps and the sample are fixedly clamped. The method uses the section method to perform stress analysis on the gauge length section of each specimen, calculates the true tensile load of each specimen gauge length section, further plots the tensile stress-strain curve of each specimen, and determines the tensile proportional limit and tensile modulus of each specimen based on the curve. When the test fixture is assembled and in a tensile state, each specimen is suspended in the fixture. Because the end of the Y-shaped specimen matches the trapezoidal groove in a pair of T-shaped or rectangular clamps, the load of the testing machine can achieve tensile self-locking through this fixture / specimen assembly, thereby transferring the tensile load of the testing machine to the gauge length of each specimen; the actual tensile load of each specimen's gauge length is: P i = P -(i-1)× P g ,in P For the load of the testing machine, P g The weight of a pair of rectangular small clamps P i This represents the actual tensile load on the gauge length segment of the i-th specimen from top to bottom.

2. The method according to claim 1, characterized in that: The number n depends on the number of samples to be tested, and n is the number of samples minus 1.

3. The method according to claim 1, characterized in that: When the T-shaped clamp and the n pairs of rectangular small clamps in the middle for connecting multiple samples are fully fitted together, the depth of the trapezoidal groove formed by each pair of T-shaped clamps is less than the thickness of the sample, and the depth of the trapezoidal groove formed by each pair of rectangular small clamps is less than the thickness of the sample.

4. The method according to claim 1, characterized in that: The width of the "I-shaped" portion of the two pairs of T-shaped clamps connected to the testing machine is exactly equal to the width of the testing machine's clamping block. When clamping, they are aligned with the clamping block. The ends of the T-shaped clamps have hand-held parts, which are two small rectangles resembling "wings" extending from the left and right ends of the T-shaped clamps and located outside the clamping block.

5. The method according to claim 1, characterized in that: Each pair of rectangular clamps is fixed together by bolts; one of the rectangular clamps in each pair has four identical through holes machined at its four corners, with the hole diameter slightly larger than the bolt diameter, so that the bolt can pass through smoothly; the other rectangular clamp that is paired with it has four identical threaded holes machined at its four corners, so that the bolt can be screwed in.

6. The method according to claim 1, characterized in that: The test fixture is suitable for SiC with a Y-shaped end. f Testing of tensile properties of SiC composite specimens.

7. The method according to claim 1, characterized in that: The test fixture contains at least three samples.

8. The method according to claim 1, characterized in that: The specific steps of the method are as follows: 1) Test preparation: Assemble the specimen and fixture according to the neutrality requirements to obtain the fixture / specimen assembly; 2) During the test, strain gauges were attached to the center of the front and rear surfaces of each specimen. The readings of the strain gauges attached to the front and rear surfaces of all specimens were monitored during the test. The average value of the strain gauge readings on the front and rear surfaces of each specimen was taken as the tensile strain of the specimen. 3) Load the assembly at a constant loading rate until any one of the specimens breaks. During the loading process, record the load on the testing machine and the strain data of the strain gauges attached to the surface of each specimen. 4) During the loading process, the actual tensile load on the gauge length section is calculated in real time using the section method: P i = P - ( i -1)× P g ,in P For the load of the testing machine, P g The weight of a pair of rectangular clamps; The actual stress data of each specimen during loading is obtained by dividing the actual load data of each specimen by the cross-sectional area of ​​the gauge length of the specimen; the strain of each specimen is taken as the average value of the strain gauge data attached to its front and rear surfaces. 5) Based on the tensile stress calculated for each specimen and the tensile strain measured for each specimen, plot the tensile stress-strain curve for each specimen. Determine the tensile proportional limit based on the stress level corresponding to the deviation of the tensile stress-strain curve from the initial linear segment. Calculate the tensile modulus of each specimen based on the slope of the initial linear segment of the stress-strain curve.

9. The method according to claim 8, characterized in that: The method is applicable to SiC at room temperature. f Test of the tensile proportional limit of / SiC composite materials.

10. The method according to claim 8, characterized in that: Steps 1) and 2) can be interchanged.

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