Analysis method for inverting constitutive of metal material based on indentation test

Abstract

The invention relates to the technical field of analysis and testing of mechanical properties of metal materials, in particular to an analysis method for inverting a constitutive of a metal material based on an indentation test. The method comprises the following steps: cutting cubes from a tested sample for performance testing, and carrying out surface treatment on a to-be-tested surface; performing an indentation test on the to-be-tested surface, obtaining the loading curvature and the maximum stacking height of each indentation through the indentation test so as to obtain the average loading curvature, and calculating the initial value of the constitutive parameter of the to-be-tested surface according to the average loading curvature and the maximum stacking height obtained through the test; and establishing a finite element model, inputting the initial values of the constitutive parameters into the finite element model for indentation, and carrying out iterative updating on the constitutive parameters through an iterative equation. According to the method, the deformation behavior of the material in the actual indentation test is more accurately reflected, and the interaction between the indenter and the surface to be tested can be more truly described, so that the mechanical behavior of the material is more in line with the actual situation.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical property analysis and testing of metal materials, and in particular to an analysis method for inverting the constitutive structure of metal materials based on an indentation test. Background Art

[0002] The constitutive parameters of metal materials are an important research direction in the aerospace field. These parameters are crucial to the performance of materials under extreme temperature and pressure conditions. In aerospace applications, high-strength, low-weight metal materials (such as aluminum alloys and titanium alloys) are often used for fuselage structures and engine components to ensure the stability and safety of aircraft under high loads. In this field, key mechanical performance indicators include Young's modulus, yield strength, and hardening index. These properties determine the service life and safety of metal materials and directly affect the design, manufacturing process and final performance of aircraft. In addition, the constitutive parameters of metal materials also have an important influence on their processing technology, fatigue performance, and fracture behavior, thereby promoting the advancement of aerospace technology and improving economic benefits.

[0003] Traditional tensile tests require the material to be processed into round rods or plate specimens of tens to hundreds of millimeters and carried out on large tensile testing machines. Such testing machines are bulky and difficult to move, and have different requirements for specimen size, which brings trouble to the experimenters. In addition, the process of installing the extensometer and recording the displacement is relatively cumbersome. Therefore, obtaining the constitutive parameters of the material through instrumented indentation testing has gradually become an effective and feasible alternative. This method has the advantages of small specimen size, simple shape, short experimental process and easy operation. Therefore, the method proposed in this patent combines instrumented indentation testing with high-fidelity finite element analysis, which can quickly and accurately obtain material parameters.

[0004] At present, the indentation test of materials is mainly carried out by using a sharp indenter (such as a glass indenter, a Vickers indenter, a cone indenter, etc.) or a non-sharp indenter (such as a plane indenter, a ball indenter, etc.) to obtain a load-displacement curve. Afterwards, characteristic quantities (such as loading curvature, contact stiffness, plastic work, elastic work, and residual depth, etc.) are extracted from the load-displacement curve to determine the corresponding material constitutive parameters. However, due to the combined influence of different constitutive parameters, there will be a problem of non-unique solutions, that is, a different set of material constitutive parameters may produce the same load-displacement curve.

[0005] A Chinese patent (CN117233012A) discloses a method for obtaining the strength properties of metal materials through instrumented indentation testing. The method first systematically calibrates the material parameters of the instrumented indentation test to ensure the reliability of the test results. Then, by establishing a functional relationship between the indentation parameters and the material parameters, researchers can extract the mechanical performance indicators of the material from the indentation test and finally calculate the performance characteristics of the tested material. Although this method has great application potential in theory, in practical applications, the accuracy of this functional relationship is affected by many factors, including the microstructure of the material, test conditions, and environmental factors. This lack of accuracy may significantly affect the accuracy of the prediction results, and thus affect the evaluation of material properties and subsequent engineering applications. Therefore, an analysis method based on inversion of the constitutive structure of metal materials based on indentation tests is designed. Summary of the invention

[0006] The purpose of the present invention is to provide an analytical method for inverting the constitutive structure of metal materials based on indentation tests, so as to solve the problem that the lack of accuracy in establishing a functional relationship between indentation parameters and material parameters proposed in the above background technology may significantly affect the accuracy of the prediction results, thereby affecting the evaluation of material properties and subsequent engineering applications.

[0007] To achieve the above object, the present invention provides an analysis method for inverting the constitutive structure of metal materials based on indentation test, comprising the following steps: S1. Cut a cube from the sample to be tested for performance testing. In the process of performance testing, select two faces of the six faces of the cube that are perpendicular to the direction to be tested as the test faces, and then evaluate the mechanical properties of the material in different directions. After the test faces are selected, perform surface treatment on the test faces of the cube; S2. Perform an indentation test on the surface to be tested, obtain the loading curvature and maximum stacking height of each indentation through the indentation test, thereby obtaining an average loading curvature, and calculate the initial values ​​of the constitutive parameters of the surface to be tested based on the average loading curvature and maximum stacking height obtained in the test; S3, establishing a finite element model, inputting the initial values ​​of the constitutive parameters into the finite element model for indentation, iteratively updating the constitutive parameters through iterative equations, and stopping the iteration when the preset conditions are met, and outputting the final constitutive parameter results; S4. Use the Hollomon constitutive equation to generate a stress-strain curve using the iterated material constitutive parameters.

[0008] As a further improvement of the present technical solution, in S1, the surface treatment of the test surface of the cube is specifically as follows: cross-grinding the test surface with sandpaper, polishing it with flannel after grinding, and regularly flushing the test surface with clean water during the polishing process, repeating the above steps until the test surface shows a mirror effect again.

[0009] As a further improvement of the technical solution, the specific steps of S2 are as follows: S21, using a conical indenter to set the load to a preset pressure value, making a number of indentation points on the surface to be tested, generating an indentation matrix, and recording a load-displacement curve of each indentation; S22, fit the loading part of the load-displacement curve of each indentation to obtain the loading curvature In the process of obtaining the loading curvature, the friction between the indenter and the surface to be tested and the influence of the contact surface are introduced for optimization. Finally, the average value of each loading curvature is taken to obtain the average loading curvature of the surface to be tested. ; S23, scan the indentation morphology through the laser confocal device to obtain the maximum stacking height ; S24, by comparing the average loading curvature in different indentation tests and maximum stacking height , infer the deformation characteristics of the material under different loads, and thus calculate the initial values ​​of the constitutive parameters of the surface to be tested.

[0010] As a further improvement of the technical solution, the S22 is specifically as follows: ; in, is the average loading curvature of the surface to be tested; ; is the number of indentation points; ; in, For the Load at each indentation point; For the The loading curvature of each indentation point; For the The indentation depth of each indentation point.

[0011] As a further improvement of the technical solution, in S22, the friction between the indenter and the surface to be measured and the influence of the contact surface are introduced to optimize the process of obtaining the loading curvature, and the optimization is as follows: ; in, For the The contact area of ​​each indentation point; is a constant related to the geometry of the indenter; ; in, For the Contact pressure at each indentation point; ; in, is the contribution of friction to the load; ; but: ; in, After optimization The loading curvature of each indentation point; ; in, is the average loading curvature of the tested surface after optimization.

[0012] As a further improvement of the present technical solution, the constitutive parameters in S24 include elastic modulus, yield strength and hardening index.

[0013] As a further improvement of the technical solution, the S24 elastic modulus, yield strength and hardening index are specifically obtained as follows: ; in, is the elastic modulus of the material of the surface to be tested; is the Poisson's ratio of the material; ; in, is the yield strength of the material of the surface to be tested; is the load that causes the material to yield; is the contact area at the maximum stacking height; ; in, is the hardening index of the material of the surface to be tested; is the stress of the material at the end of the indentation test; is the strain of the material at the end of the indentation test; is the yield strain.

[0014] As a further improvement of the present technical solution, in said S2, the constraint conditions for establishing the finite element model include axisymmetric boundary conditions and fixed boundary conditions; wherein the symmetric boundary condition means that the entire finite element model is axisymmetrically arranged, the indenter is located on the axis of symmetry, and the axisymmetric boundary condition is applied to the left side of the material, which can avoid deformation in the radial direction; the fixed boundary condition means that the bottom of the material is The direction is fixed, that is, all nodes at the bottom are not allowed to be Move in direction.

[0015] As a further improvement of the technical solution, in S3, the iterative update of the constitutive parameters by the iterative equation is specifically as follows: ; in, For the The elastic modulus of the iteration; For the The contact stiffness of the iteration; For the The contact stiffness of the iteration; For the The elastic modulus of the iteration; ; in, For the Yield strength of iterations; is the loading curvature of the test; For the The loading curvature of the iteration; For the Yield strength of iterations; ; in, For the The hardening index of the iteration; is the maximum stacking height of the test; For the The maximum stacking height of the iteration; For the Hardening exponent for iterations.

[0016] As a further improvement of the present technical solution, in S3, the iteration stops until a preset condition is reached, specifically: an error threshold is preset in advance, and each iteration determines whether the error result of the constitutive parameters output by the finite element model is less than the error threshold. If the error result is greater than the threshold, the iteration continues until the error result of the constitutive parameters output by the finite element model is within the error threshold, then the iteration stops and the result is output.

[0017] Compared with the prior art, the present invention has the following beneficial effects: In this analytical method for inverting the constitutive structure of metal materials based on indentation tests, the effects of friction and contact area are introduced into the loading curvature expression, thereby more accurately reflecting the deformation behavior of the material in the actual indentation test and being able to more realistically describe the interaction between the indenter and the test surface, especially under high loads. This not only improves the calculation accuracy of the loading curvature, but also enhances the reflection of the test results on the mechanical properties of the material, making the mechanical behavior of the material more consistent with the actual situation, thereby providing a more reliable basis for the subsequent derivation of constitutive parameters and mechanical properties analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flow chart of the overall method of the present invention; Figure 2 A flowchart of the overall method implementation of the present invention; Figure 3 is the load displacement curve; Figure 4 It is a schematic diagram of the maximum stacking height; Figure 5 It is a schematic diagram of stress-strain curve; Figure 6 It is the finite element model diagram; Figure 7 This is the prediction effect diagram of this method. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Example See also Figure 1 As shown, an analysis method for inverting the constitutive structure of metal materials based on indentation test is provided, which includes the following steps: S1. Cut a cube from the sample to be tested for performance testing. In the process of performance testing, select two faces of the six faces of the cube that are perpendicular to the direction to be tested as the test faces, and then evaluate the mechanical properties of the material in different directions. After the test faces are selected, perform surface treatment on the test faces of the cube; In this embodiment, a 5mm×5mm×5mm cube is cut from the material to be tested for performance testing. In order to comprehensively evaluate the mechanical properties of the material in different directions, the anisotropic properties of the material need to be considered. Specifically, when testing, it should be ensured that two of the six faces are perpendicular to the direction to be tested. This means that for each specific test direction, the corresponding cutting surface needs to be selected for the experiment. For example, if you want to evaluate the performance of the material in the X-axis direction, you should select two faces perpendicular to the X-axis for testing; similarly, for the performance evaluation in the Y-axis and Z-axis directions, you should also select faces perpendicular to these axes respectively. This ensures that the test results can truly reflect the mechanical behavior of the material in different directions, thereby providing more accurate data support for the application of the material.

[0021] In S1, the surface treatment of the test surface of the cube is specifically: using sandpaper to cross-grind the test surface, and after grinding, using flannel cloth to polish, and during the polishing process, regularly flushing the test surface with clean water, repeating the above steps until the test surface has a mirror effect again.

[0022] In this embodiment, when the surface of the cube to be tested is treated, sandpapers of 400 mesh, 800 mesh, 1200 mesh and 2000 mesh are first used to polish each surface in turn. During each polishing process, ensure that the wear marks left by the last time are completely covered to ensure the improvement of surface smoothness. The cross-polishing method is adopted during polishing, which can effectively remove the rough parts and achieve a more uniform effect. After completing the polishing, a woolen cloth is used for polishing. During the polishing process, a 2.5-micron diamond suspension is continuously used. This fine particle can further smooth the surface. At the same time, the surface to be tested is regularly rinsed with clean water to remove the residual particles and suspension generated during the polishing process to prevent it from affecting the surface quality. After multiple rounds of meticulous grinding and polishing, the surface to be tested should show a high-gloss mirror effect. This fine surface treatment significantly reduces the impact of surface roughness on subsequent performance tests.

[0023] S2. Perform an indentation test on the surface to be tested, obtain the loading curvature and maximum stacking height of each indentation through the indentation test, thereby obtaining an average loading curvature, and calculate the initial values ​​of the constitutive parameters of the surface to be tested based on the average loading curvature and maximum stacking height obtained in the test; The specific steps of S2 are as follows: S21. Use a conical indenter to set the load to a preset pressure value, make a number of indentation points on the surface to be tested, generate an indentation matrix, and record the load-displacement curve of each indentation, such as Figure 3 As mentioned above, there are two curves in the figure: one is the loading curve, which shows the relationship between load and displacement when the indenter is gradually pressed into the material; the other is the unloading curve, which shows the relationship between load and displacement when the indenter is gradually withdrawn from the material. The loading curve and the unloading curve overlap in the initial stage, and then separate to form an annular area, which reflects the elastic recovery and plastic deformation of the material. The contact stiffness (S) is marked in the figure, which is determined by the slope of the unloading curve and is used to calculate the hardness and other mechanical properties of the material; S22, fit the loading part of the load-displacement curve of each indentation to obtain the loading curvature In the process of obtaining the loading curvature, the friction between the indenter and the surface to be tested and the influence of the contact surface are introduced for optimization. Finally, the average value of each loading curvature is taken to obtain the average loading curvature of the surface to be tested. ; S22 is as follows: ; in, is the average loading curvature of the surface to be tested; ; is the number of indentation points; ; in, For the Load at each indentation point; For the The loading curvature of the indentation point is the average of the loading curvatures of the nine points; For the The indentation depth of each indentation point; When performing an indentation test, multiple indentation points are usually placed on the surface to be tested to form an indentation matrix. The loading curvature C of each indentation point may vary due to local differences in the specimen, surface unevenness, or even slight changes in experimental conditions. Therefore, by calculating the loading curvature of multiple indentation points and taking their average value, the influence of local errors or accidental errors can be effectively reduced, making the measurement results more stable and reliable.

[0024] In S22, the friction between the indenter and the surface to be tested and the influence of the contact surface are introduced to optimize the process of obtaining the loading curvature. After optimization, the specific results are: ; in, For the The contact area of ​​each indentation point; is a constant related to the indenter geometry. For a conical indenter, k can be determined based on the cone angle and other geometric features of the indenter; ; in, For the Contact pressure at each indentation point; ; in, is the contribution of friction to the load; ; but: ; in, After optimization The loading curvature of each indentation point; ; in, is the average loading curvature of the surface to be tested after optimization; The optimized loading curvature expression introduces the effects of friction and contact area, thus more accurately reflecting the deformation behavior of the material in the actual indentation test. In the traditional model, ignoring the changes in friction and contact area may lead to inaccurate estimation of the material constitutive relationship. The optimized expression can more realistically describe the interaction between the indenter and the surface to be tested by considering these factors, especially under high loads. This not only improves the calculation accuracy of the loading curvature, but also enhances the reflection of the test results on the mechanical properties of the material, making the mechanical behavior of the material more in line with the actual situation, and thus providing a more reliable basis for the subsequent derivation of constitutive parameters and mechanical performance analysis.

[0025] S23, scan the indentation morphology through the laser confocal device to obtain the maximum stacking height ,like Figure 4 As shown; During the indentation process, there is a certain relationship between the loading curvature and the stacking height. The loading curvature is a quantitative reflection of the relationship between the load applied by the indenter and the indentation depth, while the maximum stacking height is a direct result of the local deformation of the material. By comparing the loading curvature and the maximum stacking height in different indentation tests, the deformation characteristics of the material under different loads can be inferred, and the constitutive parameters such as the hardness and elastic modulus of the material can be further calculated. S24, by comparing the average loading curvature in different indentation tests and maximum stacking height , infer the deformation characteristics of the material under different loads, and thus calculate the initial values ​​of the constitutive parameters of the surface to be tested; The constitutive parameters of S24 include elastic modulus, yield strength and hardening exponent.

[0026] The specific acquisition of S24 elastic modulus, yield strength and hardening index is as follows: ; in, is the elastic modulus of the material of the surface to be tested, which reflects the material's ability to resist deformation in the elastic stage; is the Poisson's ratio of the material, usually estimated experimentally or theoretically; ; in, is the yield strength of the material of the surface to be tested, which describes the critical load for the material to enter the plastic deformation zone from the elastic zone; is the load that causes the material to yield; is the contact area at the maximum stacking height, which is usually related to the relationship between the indentation depth and the contact area; ; in, The hardening index of the material on the surface to be tested describes the stress enhancement behavior of the material during the plastic deformation stage, that is, the hardening characteristics of the material after yielding. The hardening index can be calculated by observing the changes in the indentation morphology and loading curvature of the material during the loading process; is the stress of the material at the end of the indentation test; is the strain of the material at the end of the indentation test; is the yield strain; In the embodiment, S2 uses a conical indenter with a cone angle of 140.6° and a tip radius of 15 microns to press the load down to 30N. Considering the influence of experimental uncertainty, 9 points are made on one surface at intervals of 1mm to form a 3×3 indentation matrix. Subsequently, the load-displacement curve of each indentation is obtained. For the loaded part of the obtained curve, the loading curvature is obtained by the above formula Finally, the average of the nine loading curvatures was taken to obtain the average loading curvature, and the indentation morphology was scanned by a laser confocal device to obtain the maximum stacking height.

[0027] S3, establish a finite element model, such as Figure 6 As shown, the initial values ​​of the constitutive parameters are input into the finite element model for indentation, and the constitutive parameters are iteratively updated through the iterative equation until the preset conditions are met, then the iteration stops and the final constitutive parameter results are output. The yield strength ranges from 100MPa to 1000MPa, and the hardening exponent ranges from 0 to 0.5. When the error between the finite element results and the test results is within 0.5%, the iteration stops and the results are output.

[0028] In S2, the constraints for establishing the finite element model include axisymmetric boundary conditions and fixed boundary conditions; the symmetric boundary condition means that the entire finite element model is axisymmetric, the indenter is located on the symmetry axis, and the axisymmetric boundary condition is applied to the left side of the material to avoid deformation in the radial direction; the fixed boundary condition means that the bottom of the material is The direction is fixed, that is, all nodes at the bottom are not allowed to be The movement in the right direction ensures that when the pressure head is pressed downward into the material, the bottom of the material does not deform.

[0029] Specifically: The indentation test was simulated using the commercial finite element software ABAQUS. The entire indentation test model is an axisymmetric model, in which the indenter is a rigid body and the pressed material is a deformable body. The cone angle of the indenter is consistent with the experimental indenter and is set to 140.6°. The size of the pressed material is 1mm×1mm, containing 10740 4-node bilinear axisymmetric quadrilateral elements, using reduced integration and hourglass control (C3D8R). In the area below the indenter, the element size is a minimum of 6 microns. An axisymmetric boundary condition is applied to the left side of the sample, and its bottom is fixed in the y direction. The indentation test is simulated by load control, and the indenter is subjected to a reaction force of 30N, and then its position is restored in the unloading step. Since the friction between the indenter and the pressed material has little effect on the results, it is set to a frictionless state.

[0030] In S3, the iterative update of constitutive parameters through iterative equations is as follows: ; in, For the The elastic modulus of the iteration; For the The contact stiffness of the iteration; For the The contact stiffness of the iteration; For the The elastic modulus of the iteration; ; in, For the Yield strength of iterations; is the loading curvature of the test; For the The loading curvature of the iteration; For the Yield strength of iterations; ; in, For the The hardening index of the iteration; is the maximum stacking height of the test; For the The maximum stacking height of the iteration; For the The hardening index of the iteration; In S3, the iteration stops until the preset conditions are met, specifically: an error threshold is preset in advance, and each iteration determines whether the error result of the constitutive parameters output by the finite element model is less than the error threshold. If the error result is greater than the threshold, the iteration continues until the error result of the constitutive parameters output by the finite element model is within the error threshold, then the iteration stops and the result is output.

[0031] S4. Use the Hollomon constitutive equation to generate a stress-strain curve using the iterated material constitutive parameters, such as Figure 5 As shown. Finally, the prediction effect of this method is obtained, as shown Figure 7 As shown, the figure contains two curves: the black curve represents experimental data and the red curve represents predicted data. The horizontal axis represents strain and the vertical axis represents stress. It can be seen from the figure that the predicted curve is very close to the experimental curve in most areas, especially in the low strain range. The material parameter values ​​obtained by tensile test and the parameter values ​​predicted by this method are listed below the table, including elastic modulus, yield strength and hardening exponent, and the error percentage between the predicted value and the experimental value is given. These data show the effectiveness of this method in predicting the mechanical properties of metal materials.

[0032] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only preferred examples of the present invention, and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. An analytical method for inverting the constitutive structure of metal materials based on indentation test, characterized by: The steps include: S1. Cut a cube from the sample to be tested for performance testing. In the process of performance testing, select two faces of the six faces of the cube that are perpendicular to the direction to be tested as the test faces, and then evaluate the mechanical properties of the material in different directions. After the test faces are selected, perform surface treatment on the test faces of the cube; S2. Perform an indentation test on the surface to be tested, obtain the loading curvature and maximum stacking height of each indentation through the indentation test, thereby obtaining an average loading curvature, and calculate the initial values ​​of the constitutive parameters of the surface to be tested based on the average loading curvature and maximum stacking height obtained in the test; S3, establishing a finite element model, inputting the initial values ​​of the constitutive parameters into the finite element model for indentation, iteratively updating the constitutive parameters through iterative equations, and stopping the iteration when the preset conditions are met, and outputting the final constitutive parameter results; S4. Use the Hollomon constitutive equation to generate a stress-strain curve using the iterated material constitutive parameters.

2. The analysis method for inverting the constitutive structure of metal materials based on indentation test according to claim 1 is characterized by: In S1, the surface treatment of the test surface of the cube is specifically: using sandpaper to cross-grind the test surface, and after grinding, using flannel cloth to polish, and during the polishing process, regularly flushing the test surface with clean water, repeating the above steps until the test surface has a mirror effect again.

3. The analysis method for inverting the constitutive structure of metal materials based on indentation test according to claim 2 is characterized by: The specific steps of S2 are as follows: S21, using a conical indenter to set the load to a preset pressure value, making a number of indentation points on the surface to be tested, generating an indentation matrix, and recording a load-displacement curve of each indentation; S22, fit the loading part of the load-displacement curve of each indentation to obtain the loading curvature In the process of obtaining the loading curvature, the friction between the indenter and the surface to be tested and the influence of the contact surface are introduced for optimization. Finally, the average value of each loading curvature is taken to obtain the average loading curvature of the surface to be tested. ; S23, scan the indentation morphology through laser confocal equipment to obtain the maximum stacking height ; S24, by comparing the average loading curvature in different indentation tests and maximum stacking height , infer the deformation characteristics of the material under different loads, and thus calculate the initial values ​​of the constitutive parameters of the surface to be tested.

4. The analysis method for inverting the constitutive structure of metal materials based on indentation test according to claim 3 is characterized by: The S22 is specifically as follows: ； in, is the average loading curvature of the surface to be tested; ; is the number of indentation points; ； in, For the Load at each indentation point; For the The loading curvature of each indentation point; For the The indentation depth of each indentation point.

5. The analysis method for inverting the constitutive structure of metal materials based on indentation test according to claim 4 is characterized by: In S22, the friction between the indenter and the surface to be tested and the influence of the contact surface are introduced to optimize the process of obtaining the loading curvature. After optimization, the specific results are: ； in, For the The contact area of ​​each indentation point; is a constant related to the geometry of the indenter; ； in, For the Contact pressure at each indentation point; ； in, is the contribution of friction to the load; ； but: ； in, After optimization The loading curvature of each indentation point; ； in, is the average loading curvature of the tested surface after optimization.

6. The analysis method for inverting the constitutive structure of metal materials based on indentation test according to claim 5 is characterized by: The constitutive parameters in S24 include elastic modulus, yield strength and hardening exponent.

7. The analysis method for inverting the constitutive structure of metal materials based on indentation test according to claim 6 is characterized by: The S24 elastic modulus, yield strength and hardening index are specifically obtained as follows: ； in, is the elastic modulus of the material of the surface to be tested; is the Poisson's ratio of the material; ； in, is the yield strength of the material of the surface to be tested; is the load that causes the material to yield; is the contact area at the maximum stacking height; ； in, is the hardening index of the material of the surface to be tested; is the stress of the material at the end of the indentation test; is the strain of the material at the end of the indentation test; is the yield strain.

8. The analysis method for inverting the constitutive structure of metal materials based on indentation test according to claim 7 is characterized by: In S2, the constraint conditions for establishing the finite element model include axisymmetric boundary conditions and fixed boundary conditions; wherein the symmetric boundary condition means that the entire finite element model is axisymmetrically set, the indenter is located on the symmetry axis, and the axisymmetric boundary condition is applied to the left side of the material to avoid deformation in the radial direction; the fixed boundary condition means that the bottom of the material is The direction is fixed, that is, all nodes at the bottom are not allowed to be Move in direction.

9. The method for analyzing the constitutive structure of metal materials based on indentation test according to claim 8, characterized in that: In S3, the iterative update of the constitutive parameters by the iterative equation is specifically as follows: ； in, For the The elastic modulus of the iteration; For the The contact stiffness of the iteration; For the The contact stiffness of the iteration; For the The elastic modulus of the iteration; ； in, For the Yield strength of iterations; is the loading curvature of the test; For the The loading curvature of the iteration; For the Yield strength of iterations; ； in, For the The hardening index of the iteration; is the maximum stacking height of the test; For the The maximum stacking height of the iteration; For the The hardening exponent for the iteration.

10. The analysis method for inverting the constitutive structure of metal materials based on indentation test according to claim 9, characterized in that: In S3, the iteration stops until the preset conditions are met, specifically: an error threshold is preset in advance, and each iteration determines whether the error result of the constitutive parameters output by the finite element model is less than the error threshold. If the error result is greater than the threshold, the iteration continues until the error result of the constitutive parameters output by the finite element model is within the error threshold, then the iteration stops and the result is output.

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