A compound indentation method for obtaining material residual stress and stress-strain relationship

Abstract

The application provides a composite indentation method for obtaining material residual stress and stress-strain relationship, and belongs to the technical field of residual stress, and comprises the following steps: step 1: a composite indenter is used to perform a quasi-static indentation test on a measured material to obtain a continuous load-displacement curve, wherein the composite indenter is a composite structure of a plane and a cone; step 2: a loading coefficient C F and a loading index m are obtained from a load-displacement curve obtained in a plane indentation stage; step 3: a loading coefficient C C is obtained from a P-h curve obtained in a cone indentation stage; step 4: material constitutive relationship parameters and residual stress are obtained according to C F and m obtained in step 2 and C C obtained in step 3, and material stress-strain relationship is obtained.

Description

Technical Field

[0001] This invention relates to the field of residual stress technology, and more specifically to a composite indentation method for obtaining residual stress and stress-strain relationship of a material. Background Technology

[0002] Residual stress and material property testing of materials in service structures are fundamental tasks for structural integrity evaluation. Traditional mechanical property testing generally involves cutting large-sized standard specimens from the raw materials or components under test and measuring the material's mechanical properties, such as elastic modulus, stress-strain relationship, and fatigue performance, on a material testing machine through tensile, compression, bending, shearing, or fatigue methods. Residual stress is also tested through localized destructive methods such as drilling and cutting. However, with the increasing demand for material property testing of service structures and welded joints, limitations in component size and material cutting make it difficult to effectively conduct tests using traditional sampling methods. This has led to widespread attention to nano-sample testing, especially indentation testing methods for obtaining localized material mechanical properties. Developing indentation testing methods that can accurately obtain residual stress and material mechanical properties on the component surface has significant theoretical and engineering value for the safety evaluation of service structures and welded joints. Currently, accurately testing residual stress and material mechanical properties by micro-indenting a specific indenter into the component surface remains challenging. Existing testing techniques can only test material mechanical properties or component residual stress individually, as described below:

[0003] (I) Uniaxial mechanical properties of materials

[0004] (1) In 2020, Liu XK et al. published a paper entitled "Semi-analytical model for flat indentation of metalmaterials and its applications" in the journal Chinese Journal of Aeronautics, Volume 33, Issue 12, pp. 3266-3277. The paper used a cylindrical plane indenter to obtain the uniaxial stress-strain relationship of the material. For metal materials whose stress-strain relationship conforms to the power law shown in formula (9), formula (10) was proposed to describe the stress-strain relationship parameters of the material and the diameter of the plane indenter. D ,energy W and press-in displacement h A theoretical model of the relationship between them.

[0005] (9)

[0006] (10)

[0007] In the formula, EThe elastic modulus of the material being tested. For nominal yield stress, K and n These are the strain hardening coefficient and the strain hardening exponent, respectively. W * The dimensionless compressive energy, W * = KD 3 , k 1~ k 6 is a dimensionless solution constant. This method uses the energy-displacement curve of the cylindrical plane indentation, based on Gauss-Newton iteration, and employs equation (10) to perform nonlinear least-squares fitting on the energy-displacement curve, ultimately obtaining the material stress-strain relationship parameters. K , and n This method requires a tedious iterative process to solve for material parameters, making it inconvenient for engineering applications.

[0008] (2) The invention patent "Method for Predicting Uniaxial Constitutive Relationship of Materials by Double-Cone Indentation" (application number: 201610024076.7) applied by Cai Lixun et al. uses double-cone indentation with different cone angles to obtain the uniaxial stress-strain relationship of materials. Based on the principle of energy density equivalence, an arbitrary combination of cone angles was established. and Loading curvature C With material stress-strain relationship parameters ( E , and n The theoretical model between ) is, i.e.

[0009] (11)

[0010] In the formula, v * Characteristic energy density, E The elastic modulus of the material being tested. and n These are the nominal yield strength and strain hardening exponent, respectively. This method requires two conical indenters with different cone angles to perform two indentation loading operations on the test material to obtain the test load-displacement ratio, and then regress the loading curvature to obtain the load-displacement ratio. C 1 and C 2. Then, the stress-strain relationship parameters of the material are obtained by solving equation (11). This method has different pressure point positions for different cone angle indentation tests, and has high requirements for the uniformity of material properties and surface smoothness.

[0011] (ii) Residual stress

[0012] (3) The invention patent "A Method for Determining Residual Stress of Materials Based on Deviatoric Stress Equivalence" (application number: 202110073404.3) applied for by Cai Lixun et al. uses a conical indenter to predict the residual stress of materials. Based on the principles of deviatoric stress equivalence and energy density equivalence, a dimensionless residual stress is established. R With loading curvature C Material stress-strain relationship parameters ( E , and n and half cone angle The theoretical model between them, namely

[0013] (12)

[0014] In the formula, C 0 represents the loading curvature under zero residual stress. C R The loading curvature under residual stress state, This is an intermediate quantity related to the stress-strain relationship parameters of the material. The loading curvature is obtained by fitting the load-displacement curves obtained from indentation loading under no residual stress and under residual stress conditions of the tested material. C 0 and C R The residual stress is obtained using equation (12). This method requires a load-displacement curve with no residual stress as a reference, or it requires known uniaxial stress-strain parameters of the material to obtain the loading curvature. C 0.

[0015] (4) In 2014, Zhang TH et al. published “Estimation of surface equi-biaxial residual stress by using instrumented sharp indentation” in the journal Materials Science and Engineering: A, Volume 614, pp. 264-272. Based on large-scale numerical calculations, they established a dimensionless residual stress. / The relationship between the loading curvature difference and the formula:

[0016] (13)

[0017] In the formula, C The indentation curvature under residual stress state. C 0 represents the loading curvature under no residual stress. E For elastic modulus, n The strain hardening index is...a 1~ a 6 and b 1~ b 6 is a model constant. This method is based on the loading curvature. C It is determined to be compressive residual stress. C > C 0) or tensile residual stress ( C < C 0), which in turn affects the indentation curvature under residual stress. C and the loading curvature under no residual stress C Substituting 0 into equation (13) and solving for the result, we obtain the solution. This method involves a complex experimental process, requiring prior determination of the material's stress-strain parameters through tests such as tensile strength. E , and n Furthermore, it is necessary to conduct indentation tests on both stressed and stress-free materials separately, which is not conducive to the promotion and application of the indentation residual stress method. Summary of the Invention

[0018] The purpose of this invention is to provide a composite indentation method for obtaining residual stress and stress-strain relationship of materials, thereby solving the technical problem that existing technologies can only test the uniaxial mechanical properties of materials or the residual stress of components.

[0019] This invention discloses a composite indentation method for obtaining residual stress and stress-strain relationship of a material, comprising the following steps:

[0020] Step 1: A quasi-static indentation test is performed on the material under test using a composite indenter to obtain a continuous load-displacement curve. The composite indenter is a composite structure of a plane and a cone.

[0021] Step 2: Obtain the load-displacement curve during the planar indentation stage and determine the loading coefficient. C F and loading index m ;

[0022] Step 3: Obtain the cone pressing stage P - h Curve for obtaining loading coefficient C C ;

[0023] Step 4: Based on the results obtained in Step 2 C F and m and the result obtained in step 3 C C The constitutive parameters and residual stress of the material are obtained, and the stress-strain relationship of the material is also obtained.

[0024] Furthermore, the lower part of the composite indenter is a planar indenter, and the upper part is a conical structure, i.e., a planar-conical composite indenter.

[0025] Furthermore, the lower part of the composite indenter is a conical indenter, and the upper part is a planar structure, i.e., a conical-planar composite indenter.

[0026] Furthermore, the load in the planar pressing stage of step 2 P -displacement h The relation satisfies a good power law, that is

[0027] (14)

[0028] According to the above formula, the regression plane pressing stage P - h Curve acquisition C F and loading index m .

[0029] Furthermore, in step 3, the load during the composite indenter pressing cone pressing stage... P -displacement h Relationships satisfy the Kick law, that is...

[0030] (15)

[0031] According to the above formula, the regression cone pressing stage P - h Curve acquisition C C .

[0032] Furthermore, the method for obtaining the material constitutive parameters and residual stress in step 4 is as follows:

[0033] S1: Obtained from step 2 C F and m F Substituting into equation (16), the initial material constitutive relation parameters are solved. and n 0;

[0034] (16)

[0035] In the formula, E The elastic modulus of the material. n 0 represents the initial strain hardening exponent. and These are the initial nominal yield strength and yield strain, respectively. , D The diameter of the composite indenter plane section is the indenter diameter. k 1F ~k 4F and b ij ( i =0,1,2; j =0,1) are model constants;

[0036] S2: The result obtained in step 3 C c and the material constitutive relation parameters obtained in step S1 and n Substituting 0 into equation (17), the residual stress of the material is solved. ;

[0037] (17)

[0038] In the formula, c ij ( i =0,1,2; j =0,1) and c 3i ( i (=0,1,2) are model constants. C 0 is the loading coefficient of the load-displacement curve of the cone indentation stage under zero residual stress state, which is obtained by equation (18);

[0039] (18)

[0040] In the formula, a 1i and a 2i ( i =0, 1, 2) are the model parameters. The semi-cone angle of the conical part of the composite indenter;

[0041] S3: Apply the plane pressing stage loading index obtained in step 2. m The information obtained in step S1 and obtained in step S2 Substituting into equation (19), the strain hardening index of the material is obtained by solving. n ;

[0042] (19)

[0043] In the formula, m 0 represents the loading exponent of the load-displacement curve during the plane indentation stage under zero residual stress. d ij ( i =0,1,2; j =0,1) and d i (i =0,1) are model constants;

[0044] S4: Obtain the results from step S3 n and obtained in step 2 C F and m Substituting into equation (20) and solving for the nominal yield strength of the material yields the results. ;

[0045] (20)

[0046] Thus, the residual stress of the material was obtained by pressing it in with a composite indenter. (S2) and constitutive parameters and n (S3 and S4).

[0047] Furthermore, in step S2, if C 0> C c Then the residual stress of the component is the tensile residual stress, and the model parameters are selected as the tensile residual stress parameters; if C 0< C c If the residual stress of the component is the compressive residual stress, then the compressive residual stress parameters are selected as the model parameters.

[0048] Furthermore, the stress-strain relationship of the material in step 4 is as follows:

[0049] (twenty one)

[0050] In the formula, E The elastic modulus of the material, and n These are the nominal yield strength and strain hardening index, respectively.

[0051] Furthermore, the elastic modulus of the material E It can be easily obtained through methods such as the Oliver-Pharr method or ultrasonic measurement.

[0052] Furthermore, numerical simulations were used to determine the constants of the aforementioned model.

[0053] Furthermore, numerical simulations were performed using finite element analysis software.

[0054] Compared with the prior art, the beneficial effects of the present invention are:

[0055] 1. This invention overcomes the limitations of existing single-sphere, cone, and plane indentation techniques, which can only obtain the stress-strain relationship of the material or, under the condition of known material mechanical properties and a zero-stress reference indentation curve, can only obtain the residual stress. It proposes a novel composite indentation method that can simultaneously and accurately test the stress-strain relationship and residual stress of the material in a localized indentation area through a single composite indenter indentation. This method is efficient, universal, and accurate, facilitating widespread adoption and application. It is particularly significant for obtaining the stress-strain curves and residual stress of in-service structures and welded joints widely used in engineering fields such as aerospace, nuclear power, and oil and gas transportation. Attached Figure Description

[0056] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0057] Figure 1 This is a schematic diagram of the composite pressure head pressing method of the present invention;

[0058] Figure 2 The indentation load-displacement curve of the planar-conical composite indenter of this invention;

[0059] Figure 3 The indentation load-displacement curve of the cone-plane composite indenter of this invention;

[0060] Figure 4 The finite element analysis mesh model for the planar-cone composite indenter of this invention;

[0061] Figure 5 The present invention provides a finite element analysis mesh model for the cone-plane composite indenter.

[0062] Figure 6 The indentation load-displacement curve of the P92 steel planar-conical composite indenter of this invention;

[0063] Figure 7 This is the prediction result of the residual stress during the indentation of the P92 steel plane-cone composite indenter of the present invention;

[0064] Figure 8 The predicted stress-strain curve of the P92 steel plane-cone composite indenter of this invention is shown. Detailed Implementation

[0065] 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. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0066] A composite indentation method for obtaining residual stress and stress-strain relationship of a material includes the following steps:

[0067] Step 1: Use a composite indenter to perform a quasi-static indentation test on the material under test to obtain a continuous load-displacement curve;

[0068] Planar-conical composite indenters include two combination forms. Form ① has a planar indenter at the bottom and a conical structure at the top, i.e., a planar-conical composite indenter, such as... Figure 1 As shown in (a); Form ② has a conical indenter at the bottom and a planar structure at the top, i.e., a conical-planar composite indenter, as shown in (a). Figure 1 As shown in (b), a single quasi-static indentation loading test was performed on the material surface using a regular plane-cone or cone-plane composite indenter to obtain a continuous two-segment typical load-displacement curve with obvious inflection (see...). Figure 2 and Figure 3 ).

[0069] Step 2: The load-displacement relationship during the plane pressing stage of the combined plane and cone indenter presses in satisfies a good power law. The loading coefficient is obtained by regressing the load-displacement curve of the plane pressing stage using the power law function shown in equation (22). C F and loading index m ;

[0070] (twenty two)

[0071] Step 3: The load-displacement relationship during the cone pressing stage of the planar and conical composite indenter presses in accordance with the Kick law. The loading coefficient is obtained by regressing the load-displacement curve of the cone pressing stage using the Kick law function shown in equation (23). C C ;

[0072] (twenty three)

[0073] Step 4: Based on the results obtained in Step 2 C F and m and the result obtained in step 3 C C The constitutive parameters and residual stress of the material are obtained, and the stress-strain relationship of the material is also obtained.

[0074] elastic modulus of the tested material EIt can be easily obtained through methods such as the Oliver-Pharr method or ultrasonic measurement.

[0075] The process of obtaining the constitutive parameters and residual stress of a material, and then deriving the stress-strain relationship, is as follows:

[0076] S1: Obtained from regression in step 2 C F and m F Substitute the values ​​into the following equation to solve for the initial constitutive parameters of the material. and n 0;

[0077] (twenty four)

[0078] In the formula, E The elastic modulus of the material. n 0 represents the initial strain hardening exponent. and These are the initial nominal yield strength and yield strain, respectively. , D The diameter of the composite indenter plane section is the indenter diameter. k 1F ~ k 4F and b ij ( i =0,1,2; j =0,1) are model constants.

[0079] S2: The result obtained in step 3 C C and the material constitutive relation parameters obtained in step S1 and n Substituting 0 into the following formula, the residual stress of the material can be solved. .

[0080] (25)

[0081] In the formula, c ij ( i =0,1,2; j =0,1) and c 3i ( i (=0,1,2) are model constants. C 0 represents the loading coefficient of the cone indentation stage load-displacement curve under zero residual stress, calculated by the following formula:

[0082] (26)

[0083] In the formula,a 1i and a 2i ( i (=0,1,2) are model constants. This is the semi-cone angle of the conical portion of the composite indenter. If... C 0> C c Then the residual stress of the component is the tensile residual stress, and the model constant is the tensile residual stress constant; if C 0< C c If the residual stress of the component is the compressive residual stress, then the model constant is the compressive residual stress constant.

[0084] S3: Apply the plane pressing stage loading index obtained in step 2. m The information obtained in step S1 and obtained in step S2 Substituting into the following formula, the strain hardening index of the material can be obtained by solving. n .

[0085] (27)

[0086] In the formula, m 0 represents the loading exponent of the load-displacement curve during the plane indentation stage under zero residual stress. d ij ( i =0,1,2; j =0,1) and d i ( i =0,1) are model constants.

[0087] S4: Obtain the results from step S3 n and obtained in step 2 C F and m Substituting into the following formula, we can obtain the nominal yield strength of the material. .

[0088] (28)

[0089] Thus, the residual stress of the material was obtained through pressing with a combination of planar and conical indenters. (S2) and constitutive parameters and n (S3 and S4).

[0090] Substituting the material constitutive parameters obtained in steps S3 and S4 into the following equation:

[0091] (29)

[0092] In the formula, E The elastic modulus of the material, and n These represent the nominal yield strength and the strain hardening index, respectively. The stress-strain curve of the tested material can then be obtained.

[0093] Obtaining accurate load-displacement test curves through quasi-static indentation tests using a planar-conical composite indenter is the primary condition for the technical solution of this invention. This invention selects indenter combination form ① planar-conical composite indenter (planar stage diameter...) D The semi-cone angle of the conical stage is 0.3mm. For conventional macroscopic indentation, in order to obtain sufficient material deformation information, the indentation depth is generally selected from 130μm to 200μm; Indenter combination form ② Cone-plane composite indenter (half cone angle of the conical stage) The angle is 70.3°, and the diameter of the planar stage is... D The indentation depth is typically selected to be 100μm to 150μm (0.3mm). Due to the shallow indentation depth, the surface of the material being tested or the structure in service needs to be ground and polished to achieve a surface roughness better than 0.32μm before a quasi-static indentation test can be carried out. The loading method is as follows: Figure 1 As shown.

[0094] Methods for determining model constants:

[0095] The model constants were determined using numerical simulation. This invention employs finite element analysis software to simulate various material mechanical law parameters (…). E , and n The pressing process of combined indenters under different residual stress conditions is described. Both types of combined indenters described above are axisymmetric problems, and the following is established: Figure 4 The finite element analysis model shown is for common engineering metallic materials, with elastic modulus... E Taken as 200 GPa, nominal yield strength The hardening index is set at 200 MPa to 1000 MPa, with an interval of 200 MPa. n The values ​​range from 0.1 to 0.3, with intervals of 0.05, for a total of 25 ideal materials. The Poisson's ratio for each material is set to 0.3. (The sentence is incomplete and requires further context.) Figure 4 Different levels of residual stress were applied to the specimen as shown, with the applied residual stresses being respectively... / =-5 / 6, -2 / 3, -1 / 2, -1 / 3, -1 / 6, 0, 1 / 6, 1 / 3, 1 / 2, 2 / 3, 5 / 6, a total of 11 levels, where "-" indicates compressive residual stress. Finite element analysis was performed on 275 computational conditions with different material parameters and different combinations of residual stress to obtain simulated load-displacement curves. The load-displacement curves were then regressed to obtain values ​​for the planar indentation stage and the conical indentation stage. C F , m and C C According to the data set { E , , n , D , C F , m}( / =0, a total of 25 sets of data) and equation (24) were substituted into the numerical regression software to obtain the regression results. k 1F ~ k 4F as well as b ij According to the data set { E , , n, D , C C}( / =0, a total of 25 sets of data) and equation (26) in form, were substituted into the numerical regression software to obtain the regression results. a ij According to the data set { E , , n , D , C C , / }(125 sets of data each for pull and compression regression) and equation (25) are substituted into numerical regression software to obtain the regression results. c ij According to the data set { E , , n , D , m , / }(125 sets of data each for pull and compression regression) and equation (27) form, substituted into numerical regression software to obtain the regression results d ij .

[0096] Taking the above-mentioned planar-conical composite indenter specification as an example, the model constant values ​​are shown in the table below. Note that the model constants for other specifications of composite indenters can be determined based on the above model using finite element analysis. The unified constants refer to the constants that need to be used in the solution of tensile and compressive residual stresses.

[0097] Table 1 Model constants

[0098]

[0099] The following uses P92 pipe steel as the test material to verify the reliability of the composite indentation method for obtaining residual stress and stress-strain relationship of the material.

[0100] The first step involved applying residual stresses of 266 MPa (tensile) and 249 MPa (compressive) to two P92 steel crossbeam members using the residual stress application device described in the paper "Residual stress indentation model based on material equivalence" published by Liu XK et al. in the journal *Chinese Journal of Aeronautics*, Vol. 33, No. 12, pp. 3266-3277. Uniaxial tensile specimens were prepared from the P92 steel raw material, and tensile tests were conducted according to GB / T 228.1-2021 *Metallic Materials - Tensile Testing - Part 1: Tensile Testing at Room Temperature* to obtain the stress-strain relationship of the material, which was then compared with the stress-strain curve obtained by the composite indentation test method.

[0101] The second step involves using a planar-cone composite indenter (planar stage diameter) on the IMTS-R indenter. D The semi-cone angle of the conical stage is 0.3 mm. Quasi-static indentation tests were conducted on P92 steel specimens #1 and #2 with pre-applied residual stress (70.3°) to obtain the test load-displacement curves, as shown below. Figure 6 As shown;

[0102] The third step is to obtain the plane loading coefficients by power-law regression for the plane indentation stage and by Kick-law regression for the cone indentation stage of the load-displacement curve. C F Loading index m and cone indentation loading coefficient C C ;

[0103] Fourth step, according to step 4 in the above specific implementation method, C F , m and C CSubstituting into the equation, we obtain the uniform residual stress on the component surface and the stress-strain relationship of the material.

[0104] Figure 7 A comparison is given between the predicted residual stress value and the pre-applied actual residual stress value of the present invention. The relative errors between the indentation test results of the two specimens and the preset residual stress are 6.67% and 3.61%, respectively. Figure 8 The stress-strain curves predicted by the present invention are compared with those obtained by traditional uniaxial tensile tests. The goodness of performance of both is better than that of 98.0%, indicating that the present invention has good prediction accuracy for residual stress and stress-strain relationship of materials.

[0105] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments based on the inspiration of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A combined indentation method for obtaining material residual stresses and stress-strain relations, characterized in that: Includes the following steps: Step 1: A quasi-static indentation test is performed on the material under test using a composite indenter to obtain a continuous load-displacement curve. The composite indenter is a composite structure of a plane and a cone. Step 2: Obtain the loading coefficient from the load-displacement curve during the plane indentation stage. C F and loading index m ; Step 3: Obtain the loading coefficient from the load-displacement curve during the cone indentation stage. C C ; Step 4: Based on the results obtained in Step 2 C F and m and the result obtained in step 3 C C The constitutive parameters and residual stress of the material are obtained, and the stress-strain relationship of the material is also obtained. The composite indenter is a planar-conical composite indenter with a planar indenter at the bottom and a conical structure at the top, wherein the diameters of the parts where the planar indenter and the conical structure meet are equal. Alternatively, the composite indenter may be a cone-plane composite indenter with a conical structure at the bottom and a planar structure at the top, wherein the diameters of the parts where the conical structure and the planar structure meet are equal; The method for obtaining the material constitutive parameters and residual stress in step 4 is as follows: S1: Obtained from step 2 C F and m Substituting into equation (3), the initial material constitutive relation parameters are solved. and n 0; (3) In the formula, E The elastic modulus of the material. n 0 represents the initial strain hardening exponent. and These are the initial nominal yield strength and yield strain, respectively. , D The diameter of the composite indenter plane section is the indenter diameter. k 1F ~ k 4F and b ij Let be the model constant, where i =0,1,2; j =0,1, where n is the strain hardening exponent of the material; S2: The result obtained in step 3 C C and the initial material constitutive relation parameters obtained in step S1 and n Substituting 0 into equation (4), the residual stress of the material is solved. ; (4) In the formula, c ij and c 3i These are model constants. C 0 is the loading coefficient obtained from the load-displacement curve of the cone indentation stage under the state of zero residual stress, which is obtained by equation (5); (5) In the formula, a 1i and a 2i For model parameters, The semi-cone angle of the conical part of the composite indenter; S3: Apply the plane pressing stage loading index obtained in step 2. m The information obtained in step S1 and obtained in step S2 Substituting into equation (6), the strain hardening index of the material is obtained by solving. n ; (6) In the formula, m 0 represents the loading exponent obtained from the load-displacement curve during the plane indentation stage under zero residual stress. d ij and d i These are model constants; S4: Obtain the results from step S3 n and obtained in step 2 C F and m Substituting into equation (7) yields the nominal yield strength of the material. ; (7) Thus, the residual stress of the material was obtained by pressing it in with a composite indenter. and constitutive relation parameters and n .

2. The composite indentation method for obtaining residual stress and stress-strain relationship of a material according to claim 1, characterized in that: The load during the planar pressing stage in step 2 P -displacement h The relation satisfies a good power law, that is (1) According to the above formula, the regression plane pressing stage P - h Curve acquisition C F and loading index m .

3. The composite indentation method for obtaining residual stress and stress-strain relationship of a material according to claim 1, characterized in that: The load during the cone pressing stage in step 3 P -displacement h Relationships satisfy the Kick law, that is... (2) According to the above formula, the regression cone pressing stage P - h Curve acquisition C C .

4. The composite indentation method for obtaining residual stress and stress-strain relationship of a material according to claim 1, characterized in that: In step S2, if C 0> C c Then the residual stress of the component is the tensile residual stress, and the model constant is the tensile residual stress constant; if C 0< C c If the residual stress of the component is the compressive residual stress, then the model constant is the compressive residual stress constant.

5. The composite indentation method for obtaining residual stress and stress-strain relationship of a material according to claim 1, characterized in that: The stress-strain relationship of the material in step 4 is as follows: (8) In the formula, E The elastic modulus of the material, and n These are the nominal yield strength and strain hardening index, respectively.

6. The composite indentation method for obtaining residual stress and stress-strain relationship of a material according to claim 1, characterized in that: elastic modulus of material E It can be easily obtained through the Oliver-Pharr method or ultrasonic measurement.

7. The composite indentation method for obtaining residual stress and stress-strain relationship of a material according to claim 1, characterized in that: The constants of the above model were determined using numerical simulation.

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