Method for simulating fatigue small crack propagation of polycrystalline metal material

Abstract

The invention relates to a method for simulating fatigue small crack propagation of a polycrystalline metal material. The method comprises the following steps: determining a crystal plastic constitutive model and accurate values of all undetermined parameters of the crystal plastic constitutive model; establishing a crack propagation finite element model of the polycrystalline metal material, and embedding the crystal plasticity constitutive model of which each undetermined parameter has a respective accurate value and a pre-obtained crack propagation criterion into the crack propagation finite element model; applying load and boundary conditions to the crack propagation finite element model, and performing crack propagation finite element analysis to obtain a finite element analysis result, including stress-strain data calculated based on the crystal plasticity constitutive model and crack propagation data calculated based on a crack propagation criterion and the stress-strain data. According to the method for simulating the fatigue small crack growth of the polycrystalline metal material, the Hall epicy size effect is introduced into the crystal plasticity constitutive model to consider the influence of the grain size on the sliding resistance, so that the simulation accuracy is improved.

Description

Technical Field

[0001] The invention relates to the technical field of fatigue numerical simulation, and more specifically to a method for simulating the propagation of small fatigue cracks in polycrystalline metal materials. Background Art

[0002] In engineering, the service load at which fatigue failure occurs is lower than the yield point of the material. However, although safety factors are considered after design and inspection schedules are established, more than 80% of parts cannot be detected by non-destructive testing during the service life (penetration of liquids, etc.), simply because the crack size is too small (less than 1mm). It is necessary to analyze the sensitivity of cracks from a microscopic perspective. The entire fatigue crack growth stage is divided into two stages: stage I is related to small fatigue crack growth (FSCG), and stage II is related to long fatigue cracks (LCG). During the entire fatigue life, the time of fatigue small crack growth accounts for more than 85% of the total time. Predicting the growth of fatigue cracks at the microstructural level is of great significance to many engineering industries. The diversity of crack growth on the length scale of the microstructure requires the use of current modeling techniques to accurately predict fatigue life. In polycrystalline microstructures, short crack paths have a great influence on the crack growth rate, but it is difficult to accurately predict, especially in the prediction of small crack growth in HCP (close-packed hexagonal lattice structure) materials.

[0003] Crystal plasticity theory is a theory that describes the deformation behavior of materials at a microscopic scale. It can consider the influence of grain orientation, grain size and grain boundary on the crack propagation path and rate. It is particularly important in the research field of small fatigue crack propagation in polycrystalline materials. In the process of studying crack propagation behavior, there are many theoretical models that can describe this characteristic, such as the commonly used node release technology (VCCT), cohesive force model method (CZM), and extended finite element technology (XFEM). Among them, with the development of computer technology, the XFEM method has obvious advantages. XFEM has the flexibility to simulate any path of crack initiation and propagation. This flexibility enables this method to simulate crack propagation without re-meshing. This XFEM is used to simulate dynamic crack propagation. The effect is better, and a large part of the workload of re-meshing can be reduced during the simulation process. At the same time, XFEM is also the most accurate model, which is more suitable for predicting small fatigue crack propagation.

[0004] In the existing XFEM-based research on fatigue crack propagation at the microscale, numerical simulation of material fatigue crack propagation has been achieved. However, the existing crystal plasticity constitutive model does not consider the effect of grain size on slip resistance, so the accuracy of its simulation results for polycrystalline metal materials is low. Summary of the invention

[0005] The purpose of the present invention is to provide a method for simulating the growth of small fatigue cracks in polycrystalline metal materials, and to introduce the Hall-Petch size effect into the crystal plasticity constitutive model to consider the influence of grain size on the slip resistance, thereby improving the accuracy of the simulation.

[0006] Based on the above purpose, the present invention provides a method for simulating small fatigue crack growth of polycrystalline metal materials, comprising:

[0007] Determine the crystal plasticity constitutive model and the accurate values ​​of each unknown parameter of the crystal plasticity constitutive model;

[0008] A crack propagation finite element model of a polycrystalline metal material is established, and a crystal plasticity constitutive model in which each parameter to be determined has its own accurate value and a pre-acquired crack propagation criterion are embedded in the crack propagation finite element model;

[0009] Loads and boundary conditions are applied to the crack propagation finite element model, and crack propagation finite element analysis is performed to obtain finite element analysis results; the finite element analysis results include stress-strain data of the crack propagation finite element model calculated based on the crystal plasticity constitutive model and crack propagation data of the crack propagation finite element model calculated based on the crack propagation criterion and stress-strain data.

[0010] Furthermore, the crystal plasticity constitutive model includes a kinematic model, a thermally activated flow law model and a kinematic hardening model.

[0011] Furthermore, the kinematic model includes:

[0012] F=F e F p

[0013]

[0014] Among them, F is the deformation gradient tensor, F e represents elastic deformation, F p represents the nonlinear plastic response, L p is the plastic velocity gradient, is the slip rate on the α slip system, m is the slip direction, n is the normal of the slip plane, N is the number of slip systems, α is a positive integer, and α∈[1,N].

[0015] Furthermore, the thermally activated flow law model includes:

[0016]

[0017]

[0018] h αβ =h s [ω+(1-ω)δαβ ]

[0019]

[0020] in, is the reference slip rate, X α and S α are the kinematic hardening and sliding resistance of the sliding system α, T is the absolute temperature, k is the Boltzmann constant, τ α is the decomposition of shear stress, sgn is the sign function, p and q are the exponential and pre-exponential parameters respectively, F 0 The free energy required to overcome the lattice resistance; τ 0 is the lattice friction stress at the current temperature; the function is bracketed by <.> so that for z ≥ 0, <z>≡z, otherwise <z>≡0;S sat is the saturated slip resistance, and its initial value is S 0 ;h s is the metal material parameter, δ αβ is the Kronecker function, ω is the potential hardening ratio; S 0 * is the initial slip resistance with normal grain size, k s is the affected slope coefficient and d is the size of the considered grain.

[0021] Furthermore, the kinematic hardening model includes:

[0022]

[0023] Among them, r D is a dynamic response parameter, h b is the hardening modulus, h b * is the critical hardening modulus of the uniform grain structure, k b is the hardening parameter induced by heterogeneous deformation, d n is the average size of the grains around the considered grain;

[0024] F 0 , τ 0 、ω、 p, q, S 0 * , k s 、h s 、r D 、h b , k b All parameters are pending.

[0025] Furthermore, S 0 * , k s As the first parameter, divide S 0 * , k s The other undetermined parameters other than are taken as the second parameters; the accurate values ​​of the undetermined parameters of the crystal plasticity constitutive model are determined, including:

[0026] Obtaining a first sample and a second sample made of a polycrystalline metal material, wherein the first sample and the second sample have different grain sizes;

[0027] Performing a quasi-static tensile test on the first sample and the second sample at room temperature to obtain stress-strain curves of the first sample and the second sample respectively;

[0028] respectively obtaining microstructure information of the first sample and the second sample, including average grain size and crystal orientation information;

[0029] A cubic crystal plasticity simulation model of the first sample is established according to the microstructure information of the first sample as a first simulation model; a crystal plasticity constitutive model in which each first parameter has a preset fixed value is used as the first crystal plasticity constitutive model, the first crystal plasticity constitutive model is embedded in the first simulation model, and a simulation analysis is performed on the first simulation model to obtain a stress-strain curve of the first simulation model;

[0030] Keeping the fixed values ​​of the first parameters of the first crystal plasticity constitutive model unchanged, and adjusting the values ​​of the second parameters of the first crystal plasticity constitutive model, so that the stress-strain curve of the first simulation model has the same shape as the stress-strain curve of the first sample; obtaining the values ​​of the second parameters at this time as the accurate values ​​of the second parameters;

[0031] A cubic crystal plasticity simulation model of the second sample is established according to the microstructure information of the second sample as the second simulation model; a crystal plasticity constitutive model in which the values ​​of each second parameter have respective accurate values ​​is used as the second crystal plasticity constitutive model, the second crystal plasticity constitutive model is embedded in the second simulation model, and a simulation analysis is performed on the second simulation model to obtain a stress-strain curve of the second simulation model;

[0032] The values ​​of the second parameters of the second crystal plasticity constitutive model are kept unchanged, and the values ​​of the first parameters of the second crystal plasticity constitutive model are adjusted so that the stress-strain curve of the second simulation model is consistent with the stress-strain curve of the second specimen; the values ​​of the first parameters at this time are obtained as the accurate values ​​of the first parameters.

[0033] Furthermore, a crack propagation finite element model of polycrystalline metal materials is established, specifically including:

[0034] Obtaining a third sample made of a polycrystalline metal material, wherein the third sample comprises a first portion and a second portion, and a prefabricated crack is provided on the second portion;

[0035] Acquiring microstructure information of the second portion of the third sample;

[0036] Establishing a geometric model of the third sample, wherein the geometric model includes a macroscopic part and a microscopic part, wherein the macroscopic part is constructed according to the first part of the third sample, and the microscopic part is constructed according to the microstructural information of the second part of the third sample;

[0037] The macroscopic part and the microscopic part are meshed respectively, and isotropic parameters are assigned to the macroscopic part. The macroscopic part and the microscopic part are connected in a common node manner to transfer stress and deformation, so as to obtain a crack propagation finite element model.

[0038] Furthermore, a crystal plasticity constitutive model in which each undetermined parameter has its own accurate value and a pre-acquired crack growth criterion are embedded in the crack growth finite element model, specifically including:

[0039] A crystal plasticity constitutive model in which each undetermined parameter has its own accurate value and a pre-acquired crack growth criterion are embedded into the microscopic part of the crack growth finite element model.

[0040] Furthermore, the crack extension criterion is a cumulative strain energy criterion, and the cumulative strain energy criterion includes:

[0041]

[0042]

[0043] Among them, G α is the accumulated strain energy value of slip system α, G max is the maximum value of the accumulated strain energy of each slip system, G crit is the preset critical value of cumulative strain energy, tol is the tolerance;

[0044] like satisfy The crack initiation standard is reached, and the crack propagation direction is G max The corresponding sliding direction of the slip system.

[0045] The method for simulating the growth of small fatigue cracks in polycrystalline metal materials of the present invention introduces the Hall-Page size effect equation into the crystal plasticity constitutive model, allocates the sliding resistance ratio in the parameters according to the experimental conditions, combines the extended finite element method, and defines the cracking criterion of the cumulative strain energy. It can more accurately describe the influence of the microstructure on the deflection and rate of the growth of small fatigue cracks, and can describe the microscopic small fatigue crack growth behavior of polycrystalline metal materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flowchart of a method for simulating small fatigue crack growth of a polycrystalline metal material according to an embodiment of the present invention;

[0047] Figure 2 A schematic diagram of the structure of a cubic crystal plasticity simulation model according to an embodiment of the present invention;

[0048] Figure 3 A stress-strain curve diagram of a first sample, a second sample, a first simulation model, and a second simulation model according to an embodiment of the present invention;

[0049] Figure 4 This is a diagram showing the slip system activation result of a small fatigue crack propagation according to an embodiment of the present invention;

[0050] Figure 5 A schematic diagram of a curve of crack length and cycle number obtained after finite element analysis of a third sample with a first grain size and a second grain size according to an embodiment of the present invention;

[0051] Figure 6 Schematic diagram of a curve of crack growth rate and stress intensity factor (ΔK) obtained after finite element analysis of a third sample with a first grain size and a second grain size according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.

[0053] like Figure 1 As shown, an embodiment of the present invention provides a method for simulating small fatigue crack growth of a polycrystalline metal material, which includes the following steps S100-S300:

[0054] S100: Determine the crystal plasticity constitutive model and accurate values ​​of various undetermined parameters of the crystal plasticity constitutive model.

[0055] The crystal plasticity constitutive model predicts the mechanical behavior of materials under external loads and their relationship with microstructure by describing microscopic plastic deformation mechanisms such as crystal slip. The crystal plasticity constitutive model includes a kinematic model, a thermally activated flow law model, and a kinematic hardening model. The kinematic model describes the geometric relationship of crystal deformation, the thermally activated flow law model defines the relationship between the plastic slip rate and the decomposed shear stress of the slip system, and the kinematic hardening model describes the interaction between the hardening and softening mechanisms, reflecting the hardening dynamic process of the slip system in the crystal.

[0056] The kinematic model is:

[0057] F=F e F p (1)

[0058]

[0059] Among them, F is the deformation gradient tensor, F e represents elastic deformation, F p represents the nonlinear plastic response, L p is the plastic velocity gradient, is the slip rate on the α slip system, m is the slip direction, n is the normal of the slip plane, N is the number of slip systems, α is a positive integer, and α∈[1,N].

[0060] The flow law model for thermal activation is:

[0061]

[0062] in, is the reference slip rate, X α and S α are the kinematic hardening and sliding resistance of the sliding system α, T is the absolute temperature, k is the Boltzmann constant, τ α is the decomposition of shear stress, sgn is the sign function. For a given slip system, the material constants are: exponential and pre-exponential parameters p and q; F 0 The free energy required to overcome the lattice resistance; τ 0 is the lattice friction stress at the current temperature; in addition, the function is bracketed by <.> so that for z ≥ 0, <z>≡z, otherwise <z>≡0.

[0063] Slip resistance S α Can evolve into:

[0064]

[0065] Among them, S sat is the saturated slip resistance, and its initial value is S 0 , β is a positive integer and β∈[1,N], h αβ is the slip hardening matrix. αβ Can evolve into:

[0066] h αβ =h s [ω+(1-ω)δ αβ ] (5)

[0067] Among them, h s is the metal material parameter, δ αβ is the Kronecker function, ω is the potential hardening ratio. The hardening matrix h αβ Represents cross hardening between slip systems.

[0068] Here, the Hall-Petch size effect equation is introduced to reflect the initial sliding resistance caused by grain boundary hardening, S 0 The expression is:

[0069]

[0070] Among them, S 0 * is the initial slip resistance with normal grain size, k s is the slope of the Hall-Page size effect equation, and d is the size of the grain under consideration.

[0071] The kinematic hardening model is as follows:

[0072]

[0073] Among them, r D is a dynamic response parameter, h b Represents the hardening modulus, which is related to the material properties.

[0074] In the above crystal plasticity constitutive model, F 0 , τ 0 、ω、 p, q, S 0 * , k s 、h s 、r D 、h b , k b All parameters are pending.

[0075] In some embodiments, S 0 * , k s As the first parameter, divide S 0 * , k s The other undetermined parameters other than the first parameter are used as the second parameters, and the method for determining the undetermined parameters includes the following steps S110-S170:

[0076] S110: obtaining a first sample and a second sample made of a polycrystalline metal material, wherein the first sample and the second sample have different grain sizes;

[0077] S120: performing a quasi-static tensile test on the first sample and the second sample at room temperature, respectively, to obtain stress-strain curves of the first sample and the second sample, respectively;

[0078] S130: respectively obtaining microstructure information of the first sample and the second sample, including average grain size (i.e., average value of grain sizes of each sample) and crystal orientation information;

[0079] S140: establishing a cubic crystal plasticity simulation model of the first sample as a first simulation model according to the microstructure information of the first sample; embedding the first crystal plasticity constitutive model into the first simulation model, and performing simulation analysis on the first simulation model to obtain a stress-strain curve of the first simulation model; wherein each first parameter of the first crystal plasticity constitutive model has a preset fixed value;

[0080] S150: keeping the fixed values ​​of the first parameters of the first crystal plasticity constitutive model unchanged, and adjusting the values ​​of the second parameters of the first crystal plasticity constitutive model so that the stress-strain curve of the first simulation model has the same shape as the stress-strain curve of the first sample; obtaining the values ​​of the second parameters at this time as the accurate values ​​of the second parameters;

[0081] S160: establishing a cubic crystal plasticity simulation model of the second sample according to the microstructure information of the second sample as the second simulation model; embedding the second crystal plasticity constitutive model into the second simulation model, and performing simulation analysis on the second simulation model to obtain a stress-strain curve of the second simulation model; wherein the values ​​of the second parameters of the second crystal plasticity constitutive model are respectively accurate values ​​of the second parameters;

[0082] S170: Keep the values ​​of the second parameters of the second crystal plasticity constitutive model unchanged, and adjust the values ​​of the first parameters of the second crystal plasticity constitutive model so that the stress-strain curve of the second simulation model is consistent with the stress-strain curve of the second specimen; obtain the values ​​of the first parameters at this time as the accurate values ​​of the first parameters.

[0083] In this way, the accurate values ​​of each first parameter and each second parameter can be obtained, that is, the accurate values ​​of each undetermined parameter can be obtained.

[0084] In step S150, since the values ​​of each first parameter are randomly assigned values, when adjusting the values ​​of each second parameter, the stress-strain curve of the first simulation model may not be completely consistent with the stress-strain curve of the first sample. At this time, it is only necessary to adjust the shapes of the two stress-strain curves to be consistent. The same shape indicates that each second parameter has been adjusted to an accurate value, but each first parameter is not an accurate value. The accurate value of each first parameter needs to be obtained by step S170. Since the accurate value of each second parameter has been obtained in step S150, in step S170, each second parameter needs to remain unchanged, and only the value of each first parameter needs to be adjusted. When each first parameter is adjusted to an accurate value, the stress-strain curve of the second simulation model will be consistent with the stress-strain curve of the second sample. The crystal plasticity constitutive model in which each first parameter and each second parameter have their own accurate values ​​can be applied to samples of any grain size, that is, samples of any grain size are simulated using the crystal plasticity constitutive model in which each first parameter and each second parameter have their own accurate values, and accurate stress-strain data can be obtained.

[0085] In some embodiments, both the first simulation model and the second simulation model can be established in ABAQUS software. For example, a 10*10*10 cubic model can be established in ABAQUS, the model includes 1000 grains, each grain is divided into a unit, and the microstructure information of the first sample is assigned to each grain to obtain the first simulation model, and then the first crystal plastic constitutive model can be written into the UMAT subroutine of the ABAQUS software to embed it into the first simulation model; then the first simulation model is subjected to the same load and boundary conditions as the quasi-static tensile test, and a simulation analysis is performed on it to obtain the stress-strain curve of the first simulation model; similarly, the microstructure information of the second sample is assigned to each grain to obtain the second simulation model, and the stress-strain curve of the second simulation model can be obtained based on the same method as the first simulation model.

[0086] In some embodiments, the grain size of the first sample is 10 microns, and the grain size of the second sample is 40 microns.

[0087] In some embodiments, the microstructure information of the first sample and the second sample can be obtained through experimental observation (such as scanning electron microscope SEM, transmission electron microscope TEM, electron backscatter diffraction EBSD, etc.) or literature research.

[0088] S200: Establishing a crack propagation finite element model of a polycrystalline metal material, and embedding a crystal plasticity constitutive model in which each undetermined parameter has its own accurate value and a pre-acquired crack propagation criterion into the crack propagation finite element model.

[0089] In some embodiments, the method for establishing a crack propagation finite element model of a polycrystalline metal material includes the following steps S210-S240:

[0090] S210: obtaining a third sample made of a polycrystalline metal material, the third sample comprising a first part and a second part, and a prefabricated crack is provided on the second part;

[0091] S220: Obtain microstructure information of the second part of the third sample; for example, it can be obtained through experimental observation (such as scanning electron microscope SEM, transmission electron microscope TEM, electron backscatter diffraction EBSD, etc.) or literature research.

[0092] S230: establishing a geometric model of the third sample, the geometric model including a macroscopic part and a microscopic part, the macroscopic part is constructed according to the first part of the third sample, and the microscopic part is constructed according to the microstructure information of the second part of the third sample;

[0093] S240: The macroscopic part and the microscopic part of the geometric model are meshed separately, and isotropic parameters (such as elastic modulus and Poisson's ratio) are assigned to the macroscopic part. The macroscopic part and the microscopic part are connected in a common node manner to transfer stress and deformation, so as to obtain a crack propagation finite element model.

[0094] The crystal plasticity constitutive model with accurate values ​​of all unknown parameters and the pre-obtained crack growth criterion are embedded in the crack growth finite element model, including:

[0095] A crystal plasticity constitutive model with accurate values ​​of all unknown parameters and a pre-acquired crack growth criterion are embedded into the microscopic part of the crack growth finite element model.

[0096] S300: applying loads and boundary conditions to the crack propagation finite element model, and performing crack propagation finite element analysis to obtain finite element analysis results; the finite element analysis results include stress-strain data of the crack propagation finite element model calculated based on the crystal plasticity constitutive model and crack propagation data of the crack propagation finite element model calculated based on the crack propagation criterion and the stress-strain data.

[0097] In some embodiments, steps S200 and S300 can be implemented using ABAQUS software. During finite element analysis, ABAQUS will call the UMAT subroutine with a pre-written crystal plasticity constitutive model to solve the stress-strain data of each slip system of the model, and call the UDMGINI subroutine with a pre-written crack extension criterion to solve the crack extension data.

[0098] In some embodiments, the crack growth criterion is a cumulative strain energy criterion, which is:

[0099]

[0100]

[0101] Among them, G α is the accumulated strain energy value of slip system α, G max is the maximum value of the accumulated strain energy of each slip system, G crit is the preset critical value of cumulative strain energy, tol is the tolerance, if If formula (9) is satisfied, the crack initiation criterion is reached and the crack extension command is executed, with the extension direction parallel to the sliding direction of the most active slip system (the slip system with the largest cumulative strain energy value is the most active slip system).

[0102] In order to speed up the calculation efficiency, set G crit =1.1; to improve convergence, set tol=0.1.

[0103] In some embodiments, the crack growth data includes crack length, crack growth rate, crack growth direction, crack tip opening and closing stress, and the like.

[0104] The following uses TA7 titanium alloy material as an example to illustrate the application of the method for simulating small fatigue crack growth in polycrystalline metal materials of the present invention.

[0105] First, the exact values ​​of the unknown parameters of the crystal plasticity constitutive model and other parameter values ​​of the material are determined. The results are shown in Table 1 below:

[0106] Table 1 The exact values ​​of the unknown parameters of the crystal plasticity constitutive model and other material parameter values

[0107] In Table 1, d1 is the grain size of the first sample, d2 is the grain size of the second sample, E is the elastic modulus, and ν is the Poisson's ratio. C11-C66 are the values ​​on the main diagonal of the local elastic stiffness matrix, and the local elastic matrix is ​​a 6-row 6-column matrix.

[0108] like Figure 2 The structure diagram of the established cubic crystal plasticity simulation model is shown in FIG. Figure 3 The stress-strain curves of the first specimen, the second specimen, the first simulation model and the second simulation model are shown. Figure 3 It can be seen that the stress-strain curve obtained by the crystal plasticity constitutive model with accurate values ​​of each unknown parameter is consistent with the stress-strain curve obtained by the quasi-static tensile test, indicating that the crystal plasticity constitutive model of the present invention has high accuracy and is applicable to specimens of different grain sizes.

[0109] After obtaining the accurate values ​​of the parameters to be determined, a crack propagation finite element model was established for the sample with an average grain size of 40 μm and a finite element analysis was performed to obtain the analysis results. Figure 4 In order to only show the effect of grain size on the growth of small fatigue cracks, without changing the model geometry and orientation information, the size of each grain in the model was reduced by 4 times to obtain a crack growth model with an average grain size of 10 μm. The crack growth rates extracted from the two models were analyzed and obtained. Figure 5 and Figure 6 It was found that fine grains have a strong hindering effect on cracks during the growth stage of small fatigue cracks, and the hindering effect gradually decreases with the increase of stress intensity factor.

[0110] The method for simulating the growth of small fatigue cracks in polycrystalline metal materials according to the embodiment of the present invention can obtain the following prediction results:

[0111] 1) Introducing the Hell-Petch effect equation into the crystal plasticity constitutive model can more accurately predict the deflection of small fatigue cracks and the initiation of slip systems.

[0112] 2) From the prediction results of crack growth rate of two grain sizes, when the crack length is within 100 microns, that is, when the stress intensity factor is relatively low, the fatigue small crack growth rate of fine grains is significantly lower than that of coarse grains, which is consistent with the experimental phenomenon.

[0113] The method for simulating the growth of small fatigue cracks in polycrystalline metal materials according to an embodiment of the present invention introduces the Hall-Page size effect equation into the crystal plasticity constitutive model, allocates the sliding resistance ratio in the parameters according to the experimental conditions, and defines the cracking criterion of the cumulative strain energy in combination with the extended finite element. It can more accurately describe the influence of the microstructure on the deflection and rate of the growth of small fatigue cracks, and can describe the microscopic small fatigue crack growth behavior of polycrystalline metal materials.

[0114] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiment of the present invention can also be modified in various ways. That is, all simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.< / z> < / z> < / z> < / z>

Claims

1. A method for simulating small fatigue crack growth in polycrystalline metal materials, characterized in that: include: Determine the crystal plasticity constitutive model and the accurate values ​​of each unknown parameter of the crystal plasticity constitutive model; A crack propagation finite element model of a polycrystalline metal material is established, and a crystal plasticity constitutive model in which each parameter to be determined has its own accurate value and a pre-acquired crack propagation criterion are embedded in the crack propagation finite element model; Loads and boundary conditions are applied to the crack propagation finite element model, and crack propagation finite element analysis is performed to obtain finite element analysis results; the finite element analysis results include stress-strain data of the crack propagation finite element model calculated based on the crystal plasticity constitutive model and crack propagation data of the crack propagation finite element model calculated based on the crack propagation criterion and stress-strain data.

2. The method for simulating small fatigue crack growth of polycrystalline metal materials according to claim 1, characterized in that: The crystal plasticity constitutive model includes a kinematic model, a thermally activated flow law model and a kinematic hardening model.

3. The method for simulating small fatigue crack growth of polycrystalline metal materials according to claim 2, characterized in that: The kinematic model includes: F=F e F p Among them, F is the deformation gradient tensor, F e represents elastic deformation, F p represents the nonlinear plastic response, L p is the plastic velocity gradient, is the slip rate on the α slip system, m is the slip direction, n is the normal of the slip plane, N is the number of slip systems, α is a positive integer, and α∈[1,N].

4. The method for simulating small fatigue crack growth of polycrystalline metal materials according to claim 3, characterized in that: The thermally activated flow law model includes: h αβ =h s [ω+(1-ω)δ αβ ] in, Reference slip rate, X α and S α are the kinematic hardening and sliding resistance of the sliding system α, T is the absolute temperature, k is the Boltzmann constant, τ α To decompose the shear stress, sgn is the sign function, p and q are the exponential and pre-exponential parameters respectively, F0 is the free energy required to overcome the lattice resistance; τ0 is the lattice friction stress at the current temperature; the function is bracketed by <.> so that for z ≥ 0, <z>≡z, otherwise <z>≡0;S sat is the saturated slip resistance, with an initial value of S0; h s is the metal material parameter, δ αβ is the Kronecker function, ω is the potential hardening ratio; S0 * is the initial slip resistance with normal grain size, k s is the affected slope coefficient and d is the size of the considered grain.< / z> < / z> 5. The method for simulating small fatigue crack growth of polycrystalline metal materials according to claim 4, characterized in that: The kinematic hardening model includes: Among them, r D is a dynamic response parameter, h b is the hardening modulus, h b * is the critical hardening modulus of the uniform grain structure, k b is the hardening parameter induced by heterogeneous deformation, d n is the average size of the grains around the considered grain; F0, τ0, ω, p、q、S0 * , k s 、h s 、r D 、h b , k b All parameters are pending.

6. The method for simulating small fatigue crack growth of polycrystalline metal materials according to claim 5, characterized in that: S0 * , k s As the first parameter, divide S0 * , k s The other undetermined parameters except are taken as the second parameters; the accurate values ​​of the undetermined parameters of the crystal plasticity constitutive model are determined, including: Obtaining a first sample and a second sample made of a polycrystalline metal material, wherein the first sample and the second sample have different grain sizes; Performing a quasi-static tensile test on the first sample and the second sample at room temperature to obtain stress-strain curves of the first sample and the second sample respectively; respectively obtaining microstructure information of the first sample and the second sample, including average grain size and crystal orientation information; A cubic crystal plasticity simulation model of the first sample is established according to the microstructure information of the first sample as a first simulation model; a crystal plasticity constitutive model in which each first parameter has a preset fixed value is used as the first crystal plasticity constitutive model, the first crystal plasticity constitutive model is embedded in the first simulation model, and a simulation analysis is performed on the first simulation model to obtain a stress-strain curve of the first simulation model; Keeping the fixed values ​​of the first parameters of the first crystal plasticity constitutive model unchanged, and adjusting the values ​​of the second parameters of the first crystal plasticity constitutive model, so that the stress-strain curve of the first simulation model has the same shape as the stress-strain curve of the first sample; obtaining the values ​​of the second parameters at this time as the accurate values ​​of the second parameters; A cubic crystal plasticity simulation model of the second sample is established according to the microstructure information of the second sample as the second simulation model; a crystal plasticity constitutive model in which the values ​​of each second parameter have respective accurate values ​​is used as the second crystal plasticity constitutive model, the second crystal plasticity constitutive model is embedded in the second simulation model, and a simulation analysis is performed on the second simulation model to obtain a stress-strain curve of the second simulation model; The values ​​of the second parameters of the second crystal plasticity constitutive model are kept unchanged, and the values ​​of the first parameters of the second crystal plasticity constitutive model are adjusted so that the stress-strain curve of the second simulation model is consistent with the stress-strain curve of the second specimen; the values ​​of the first parameters at this time are obtained as the accurate values ​​of the first parameters.

7. The method for simulating small fatigue crack growth of polycrystalline metal materials according to claim 1, characterized in that: Establish a finite element model of crack propagation in polycrystalline metal materials, including: Obtaining a third sample made of a polycrystalline metal material, wherein the third sample comprises a first portion and a second portion, and a prefabricated crack is provided on the second portion; Acquiring microstructure information of the second portion of the third sample; Establishing a geometric model of the third sample, wherein the geometric model includes a macroscopic part and a microscopic part, wherein the macroscopic part is constructed according to the first part of the third sample, and the microscopic part is constructed according to the microstructural information of the second part of the third sample; The macroscopic part and the microscopic part are meshed respectively, and isotropic parameters are assigned to the macroscopic part. The macroscopic part and the microscopic part are connected in a common node manner to transfer stress and deformation, so as to obtain a crack propagation finite element model.

8. The method for simulating small fatigue crack growth of polycrystalline metal materials according to claim 7, characterized in that: The crystal plasticity constitutive model with accurate values ​​of all unknown parameters and the pre-obtained crack growth criterion are embedded in the crack growth finite element model, including: A crystal plasticity constitutive model in which each undetermined parameter has its own accurate value and a pre-acquired crack growth criterion are embedded into the microscopic part of the crack growth finite element model.

9. The method for simulating small fatigue crack growth of polycrystalline metal materials according to claim 1, characterized in that: The crack extension criterion is a cumulative strain energy criterion, and the cumulative strain energy criterion includes: Among them, G α is the accumulated strain energy value of slip system α, G max is the maximum value of the accumulated strain energy of each slip system, G crit is the preset critical value of cumulative strain energy, tol is the tolerance; like satisfy The crack initiation standard is reached, and the crack propagation direction is G max The corresponding sliding direction of the slip system.

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