Metal material crack simulation method

Abstract

The invention relates to a metal material crack simulation method which comprises the following steps: acquiring a cohesion model, and determining each undetermined parameter of the cohesion model; obtaining a crystal plastic constitutive model, and determining each undetermined parameter of the crystal plastic constitutive model; establishing a first microstructure finite element model of the metal material, and embedding the cohesion model and the crystal plastic constitutive model into the first microstructure finite element model; applying a tensile load and a boundary condition to the first microstructure finite element model, and performing finite element analysis to obtain a first finite element analysis result; the first finite element analysis result comprises stress-strain data calculated based on the crystal plasticity constitutive model and crack data calculated based on the cohesion model and the stress-strain data. According to the metal material crack simulation method, crack initiation and amplification behaviors of the metal material can be accurately simulated.

Description

Technical Field

[0001] The invention relates to the field of crack calculation, and more specifically to a metal material crack simulation method. Background Art

[0002] In the modern industrial field, materials play a vital role, and their performance directly affects the quality and service life of products. Various engineering projects, such as construction, aerospace, automobile manufacturing, energy equipment, etc., have strict requirements on the strength, toughness, corrosion resistance, etc. of materials. Therefore, the selection and optimization of materials have become the core links in industrial design and production. In this context, how to accurately evaluate the mechanical properties of materials, especially their performance under complex stress conditions, is particularly important.

[0003] Among many materials, metal materials have become the dominant materials in the industrial field due to their excellent mechanical properties and machinability. Compared with ceramics, plastics and other materials, metal materials not only have higher strength and toughness, but also have good electrical and thermal conductivity. These characteristics enable metal materials to maintain stable performance under extreme conditions such as high temperature, high pressure, and fatigue load, and are suitable for occasions that require high strength and high stability, such as aerospace, construction, and machinery manufacturing. Therefore, the selection of metal materials and their reliability research under different load conditions are important topics in various industries.

[0004] However, metal materials are prone to cracking under complex loads, leading to structural failure and posing major risks to industrial production and safety. Crack initiation and expansion is one of the main forms of material failure. Therefore, how to accurately simulate the crack expansion behavior in metal materials has become an important research direction in the field of materials science and engineering. Summary of the invention

[0005] The object of the present invention is to provide a metal material crack simulation method to accurately simulate the crack initiation and propagation behavior of the metal material.

[0006] Based on the above purpose, the present invention provides a metal material crack simulation method, comprising:

[0007] Acquire a cohesion model, and determine various undetermined parameters of the cohesion model;

[0008] Acquiring a crystal plasticity constitutive model, and determining various undetermined parameters of the crystal plasticity constitutive model;

[0009] Establishing a first microstructure finite element model of the metal material, and embedding the cohesive force model and the crystal plasticity constitutive model into the first microstructure finite element model;

[0010] A tensile load and boundary conditions are applied to the first microstructure finite element model, and a finite element analysis is performed to obtain a first finite element analysis result; the first finite element analysis result includes stress-strain data calculated based on the crystal plasticity constitutive model and crack data calculated based on the cohesive force model and the stress-strain data.

[0011] Furthermore, the cohesion model includes:

[0012]

[0013]

[0014] Where F is the traction force, k 1 is the stiffness in the linear elastic stage, x is the displacement, x 1 is the critical damage displacement, F max is the critical damage stress, k 2 is the slope of the traction force-displacement curve in the damage evolution stage, b is the intercept of the traction force-displacement curve in the damage evolution stage, and x 2 is the complete damage displacement, k 1 、x 1 、F max , k 2 , b and x 2 All parameters are pending.

[0015] Further, various undetermined parameters of the cohesion model are determined, specifically including:

[0016] Conduct molecular dynamics simulation on metal materials to obtain the critical damage stress, critical damage displacement and complete damage displacement of metal materials;

[0017] determining the stiffness of the linear elastic stage according to the critical damage stress and the critical damage displacement;

[0018] The slope and intercept of the traction force-displacement curve in the damage evolution stage are determined according to the critical damage stress, the critical damage displacement and the complete damage displacement.

[0019] Furthermore, the crystal plasticity constitutive model includes a kinematic model, a thermally activated flow law model and a kinematic hardening model.

[0020] Furthermore, the kinematic model includes:

[0021] F=F e F p

[0022]

[0023] Among them, F is the deformation gradient tensor, Fe 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].

[0024] Furthermore, the thermally activated flow law model includes:

[0025]

[0026]

[0027] h αβ =h s [ω+(1-ω)δ αβ ]

[0028] S sat =S 0 +S inc

[0029]

[0030] in, Plastic 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, g and q are exponential and pre-exponential parameters, respectively, and 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 , S inc is the sliding resistance added during the simulation; h s is the inherent hardening constant of metal materials, 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 slope coefficient of the size dependence and d is the size of the considered grain.

[0031] Furthermore, the kinematic hardening model includes:

[0032]

[0033]

[0034] Among them, r D is the dynamic restitution coefficient, 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;

[0035] F 0 , τ 0 、ω、 g, q, S 0 * , k s , S inc 、h s 、r D 、h b * , k b All parameters are pending.

[0036] Furthermore, various undetermined parameters of the crystal plasticity constitutive model are determined, specifically including:

[0037] Establishing a second microstructure finite element model of the metal material, embedding the crystal plasticity constitutive model into the second microstructure finite element model, applying a tensile load and boundary conditions to the second microstructure finite element model, and performing finite element analysis to obtain a stress-strain curve of the microstructure finite element model;

[0038] Conduct tensile tests on metal materials to obtain stress-strain curves of metal materials;

[0039] The values ​​of the unknown parameters of the crystal plasticity constitutive model are adjusted so that the error between the stress-strain curve of the second microstructure finite element model and the stress-strain curve obtained by the tensile test is within a preset range, so as to determine the values ​​of the unknown parameters of the crystal plasticity constitutive model.

[0040] Furthermore, a first microstructure finite element model of the metal material is established, specifically comprising:

[0041] Acquiring microstructure data of the metal material;

[0042] Establishing a geometric model based on the microstructure data;

[0043] The geometric model is meshed and assigned material properties to obtain the first microstructure finite element model.

[0044] Furthermore, the crack data includes the number of cracks and the location and size of each crack.

[0045] The metal material crack simulation method of the present invention embeds the cohesive force model and the crystal plasticity constitutive model into the microstructure finite element model of the metal material, and can obtain accurate stress-strain data and crack data after finite element analysis, thereby effectively restoring the tensile fracture behavior of the metal material and accurately predicting the tensile crack of the metal material. The method has the advantages of high precision, strong flexibility, the ability to evaluate the fracture behavior of the metal material, and intuitive display. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a flow chart of a metal material crack simulation method according to an embodiment of the present invention;

[0047] Figure 2 is a schematic diagram of stress-strain data of a metal material obtained through a tensile test and finite element simulation according to an embodiment of the present invention;

[0048] Figure 3 is a schematic diagram of simulation results of tensile cracks of a non-uniform structure metal material under different grain orientations according to an embodiment of the present invention, wherein the entire morphology of the fracture is shown;

[0049] Figure 4 A schematic diagram of simulation results of tensile cracks of a non-uniform structured metal material according to an embodiment of the present invention, wherein the initiation position and amplification direction of the cracks are shown;

[0050] Figure 5 It is a schematic diagram of optimizing the direction after analyzing the crack initiation and propagation mechanism of metal materials according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] The preferred embodiments of the present invention are given below in conjunction with the accompanying drawings and described in detail.

[0052] like Figure 1 As shown, an embodiment of the present invention provides a method for simulating cracks in a metal material, which comprises the following steps:

[0053] S100: Acquire a cohesion model and determine various undetermined parameters of the cohesion model.

[0054] The cohesive force model is a model that describes the behavior of the area near the crack tip based on the interaction force between atoms or molecules of a material (i.e., cohesive force). It can simulate the crack expansion, initiation, and final fracture process during the stress process, thereby revealing the fracture mechanism of the material. The cohesive force model can use a bilinear model to describe the relationship between the traction and displacement of metal materials. In the cohesive force model, the relationship between the traction and displacement includes three stages, namely the linear elastic stage, the damage evolution stage, and the complete failure stage. The relationship between the traction and displacement in each stage is as follows:

[0055] Linear elastic stage:

[0056] F = k 1 x(x≤x 1 ) (1)

[0057]

[0058] Where F is the traction force, k 1 is the stiffness in the linear elastic stage, x is the displacement, x 1 is the critical damage displacement, F max is the critical damage stress, k 1 、x 1 and F max All parameters are pending.

[0059] Damage evolution stages:

[0060] F = k 2 x+b(x 1 <x≤x 2 ) (3)

[0061]

[0062]

[0063] Among them, k 2 is the stiffness at the damage evolution stage (i.e., the slope of the traction-displacement curve), b is the intercept of the traction-displacement curve at the damage evolution stage, and x 2 is the complete damage displacement, k 2 , b and x 2 All parameters are pending.

[0064] Complete failure stage:

[0065] F=0,x>x 2 (6)

[0066] The cohesion model also includes:

[0067]

[0068] Among them, t n ,t s ,t t They represent the stress at a certain position of the model in the normal direction, the first shear direction, and the second shear direction, respectively. 0 n ,t 0 s ,t 0 t They represent the maximum stress of the model in the normal direction, the first shear direction, and the second shear direction, respectively. Here, t 0 n ,t 0 s ,t 0 t The value is F max When a unit satisfies the above formula (7) during the finite element analysis process, it means that cracks will occur in the unit, and the crack data of the model can be obtained.

[0069] In some embodiments, the method for determining the parameters to be determined of the cohesion model is as follows:

[0070] Molecular dynamics simulation is performed on metal materials to obtain the critical damage stress F of metal materials. max , critical damage displacement x 1 and the complete damage displacement x 2 Then, k is calculated according to formula (2): 1 , and calculate k according to formulas (4) and (5) 2 and b, in this way, all the unknown parameters of the cohesion model can be obtained, and the cohesion model is used to calculate the crack data based on the stress-strain data in the later stage. Molecular dynamics simulation is a multi-body simulation method based on computer technology. By giving the molecular system an initial motion state and using the natural motion of the molecules to extract samples in the phase space for statistical calculation, various properties and behaviors of the system can be obtained. Molecular dynamics simulation can be implemented using any suitable simulation software, including Gromacs, Amber, Namd, LAMMPS, etc.

[0071] S200: Obtain a crystal plasticity constitutive model, and determine various undetermined parameters of the crystal plasticity constitutive model.

[0072] The crystal plasticity constitutive model is based on the grain size difference strengthening model, and is obtained by evolving the slip system, crystal orientation, plastic flow and hardening mechanism according to the parameters of the metal material. The crystal plasticity constitutive model includes a kinematic model, a thermally activated flow law model and a kinematic hardening model; the kinematic model is a mathematical model about crystal deformation; the thermally activated flow law model is a mathematical model about the plastic slip rate and decomposed shear stress of the slip system; the kinematic hardening model is a mathematical model about the interaction between the soft phase and the hard phase.

[0073] The kinematic model is:

[0074] F=F e F p (8)

[0075]

[0076] 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].

[0077] The flow law model for thermal activation is:

[0078]

[0079] in, is the plastic 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 g 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.

[0080] Slip resistance S α Can evolve into:

[0081]

[0082] Among them, S sat is the saturated slip resistance, and its initial value is S 0 , which can be expressed as: S sat =S 0 +S inc , S inc is the increased slip resistance during the simulation, β is a positive integer and β∈[1,N]. Slip hardening matrix h αβ Can evolve into:

[0083] h αβ =h s [ω+(1-ω)δ αβ ]

[0084] Among them, h s is the inherent hardening constant of metal materials, δ αβ is the Kronecker function, ω is the potential hardening ratio. The hardening matrix h αβ Here, the Hall-Petch law is introduced to reflect the initial sliding resistance caused by grain boundary hardening, S 0 Evolved into:

[0085]

[0086] Among them, S 0 * is the initial slip resistance with normal grain size, k s is the slope coefficient of the size dependence, which is a parameter affected by the slope determined by the Hall-Page relationship, and d is the size of the considered grain.

[0087] The kinematic hardening model evolves as follows:

[0088]

[0089] Among them, r D is the dynamic restitution coefficient, h b represents the hardening modulus and is defined as a function of the considered grain size and the average size of the adjacent grains:

[0090]

[0091] Among them, h b * is the critical hardening modulus of the uniform grain structure, k b is the hardening parameter induced by heterogeneous deformation, d is the size of the considered grain (i.e., each grain in the model), and d n is the average size of the grains around the considered grain, d and d n All can be obtained through experiments.

[0092] The local average cumulative strain of each slip system is expressed as the cumulative equivalent plastic strain ε eq , which evolves as follows:

[0093]

[0094] Where t is the current time, τ is the integral variable, and the symbol ":" represents the double dot product of the matrix, D p is the plastic strain rate, which evolves as follows:

[0095]

[0096] Among them, L p is the plastic velocity gradient matrix, (L p ) T is the transposed matrix of the plastic velocity gradient matrix, m is the slip direction vector, and n is the normal vector of the slip surface in the slip system.

[0097] In the crystal plasticity constitutive model, the free energy F required to overcome the lattice resistance is 0 , lattice friction stress τ at current temperature 0 , potential hardening ratio ω, g, q, initial slip resistance S with normal grain size 0 * , k s , S inc 、h s 、r D , the critical hardening modulus h of uniform grain structure b * , the hardening parameter k induced by heterogeneous deformation b All parameters are pending.

[0098] In some embodiments, the method for determining the parameters to be determined of the crystal plasticity constitutive model is as follows:

[0099] A second microstructure finite element model of the metal material is established, the crystal plasticity constitutive model is embedded in the second microstructure finite element model, a tensile load and boundary conditions are applied to the second microstructure finite element model of the metal material, and a finite element analysis is performed to obtain a second finite element analysis result, the second finite element analysis result includes a stress-strain curve of the second microstructure finite element model; a tensile test is performed on the metal material to obtain the result of the tensile test, including the stress-strain curve of the metal material; the values ​​of the various undetermined parameters of the crystal plasticity constitutive model are adjusted so that the error between the stress-strain curve of the second microstructure finite element model and the stress-strain curve of the tensile test is within a preset range (that is, so that the result obtained by the finite element analysis is consistent with the test result), and the various undetermined parameters of the crystal plasticity constitutive model at this time are accurate parameter values, thereby determining the values ​​of the various undetermined parameters of the crystal plasticity constitutive model.

[0100] S300: establishing a first microstructure finite element model of the metal material, and embedding a cohesive force model and a crystal plasticity constitutive model into the first microstructure finite element model.

[0101] In some embodiments, ABAQUS software can be used to perform finite element analysis on metal materials. First, the microstructure data of the metal material, including grain shape, size distribution, grain boundary characteristics, and possible defects (such as pores, inclusions), can be obtained through experimental observation (such as scanning electron microscope SEM, transmission electron microscope TEM, electron backscatter diffraction EBSD, etc.) or literature research, and then a geometric model is established according to the microstructure data of the metal material, and then the geometric model is meshed and assigned material properties to obtain a first microstructure finite element model of the metal material. The crystal plasticity constitutive model can be stored in the UMAT subroutine of ABAQUS in code form to embed the crystal plasticity constitutive model into the first microstructure finite element model; the cohesive force model is realized by embedding the Cohesive unit in the first microstructure finite element model, and each undetermined parameter of the crystal plasticity constitutive model and the cohesive force model can be defined by the User Material module of ABAQUS software, so that each undetermined parameter is respectively associated with the crystal plasticity constitutive model and the cohesive force model.

[0102] S400: applying a tensile load and boundary conditions to the first microstructure finite element model, and performing finite element analysis to obtain a first finite element analysis result; the first finite element analysis result includes stress-strain data calculated based on a crystal plasticity constitutive model and crack data calculated based on a cohesive force model and stress-strain data.

[0103] In some embodiments, the boundary conditions may be that the left side constrains the x-direction degree of freedom, the lower side constrains the y-direction degree of freedom, and the right side applies a preset tensile load. After applying the tensile load and boundary conditions, finite element analysis can be performed. During the finite element analysis process, ABAQUS software will call the UMAT subroutine to calculate the stress-strain data of the first microstructure finite element model, and calculate the crack data based on the stress-strain data through the Cohesive unit.

[0104] In some embodiments, the crack data includes the number of cracks and the location and size (eg, length and width) of each crack.

[0105] After obtaining the crack data, the initiation mechanism and expansion law of tensile cracks can be determined based on the Schmidt factor and crack data, including when the crack breaks along the crystal, when it breaks through the crystal, under what grain orientation multiple cracks may occur, etc. The calculation formula of the Schmidt factor is:

[0106] m=cosφ·cosλ (17)

[0107]

[0108]

[0109] Where m is the Schmidt factor, φ is the angle between the external force direction and the normal of the slip surface (normal angle), λ is the angle between the external force direction and the slip direction (slip angle), is the unit vector of the slip direction, is the normal vector direction of the slip surface, is the unit vector in the direction of the applied stress.

[0110] In some embodiments, the relationship between the crack initiation mechanism and the crack expansion law and the macroscopic mechanical properties of the metal material can also be determined based on the stress-strain data and crack data of the first microstructure finite element model. Specifically, in the modeling process, each grain in the model can be given a different orientation. Therefore, through the fracture simulation of grain models with different orientations, the positions where cracks are more likely to initiate and expand can be summarized; combined with the crack expansion position and the speed of the descending section of the stress-strain curve, the direction in which the crack expands on the descending section of the stress-strain curve can be obtained, thereby guiding the regulation of the grain orientation of the metal material in the actual manufacturing process and optimizing the crack resistance of the metal material.

[0111] In some embodiments, the optimization direction of the metal material microstructure can also be determined based on the relationship between the crack initiation mechanism and expansion law and the macroscopic mechanical properties of the metal material. Specifically, the structure with the best fracture resistance can be determined through stress-strain data and crack data, thereby determining the optimization direction.

[0112] The following takes CoCrFeMnNi high entropy alloy metal material as an example to illustrate the specific application of the metal material crack simulation method of the present invention.

[0113] First, the parameters of the cohesive force model and the crystal plasticity constitutive model are determined, and the results are shown in Table 1 below:

[0114] Table 1 Undetermined parameters of the cohesive force model and crystal plasticity constitutive model

[0115] In Table 1, C11, C22, and C44 are the values ​​of the main diagonal of the elastic tensor matrix, E is the elastic modulus, and v is the Poisson’s ratio.

[0116] After determining the parameters to be determined for the cohesive force model and the crystal plasticity model, a microstructure finite element model of the metal material can be established in the ABAQUS software, and the cohesive force model and the crystal plasticity model can be embedded in the finite element model. Then, boundary conditions and loads are applied to the finite element model to obtain finite element analysis results. According to the finite element analysis results, the crack initiation mechanism and propagation law and their relationship with the macroscopic mechanical properties of the metal material and the optimization direction of the metal material microstructure can be determined. Through the crack simulation method of the embodiment of the present invention, the following prediction results can be obtained:

[0117] 1. Prediction of macroscopic mechanical properties of homogeneous and inhomogeneous polycrystalline materials:

[0118] Figure 2 The tensile stress-strain data of the metal material microstructure are shown, wherein the solid line represents the data obtained by finite element analysis, i.e., simulation data, and the circle represents the data obtained by tensile test, i.e., experimental data; Figure 2 It can be seen that the simulation data and the experimental data are in good agreement, which proves that the crystal plasticity constitutive model of the embodiment of the present invention can capture the macroscopic mechanical properties of metal materials.

[0119] 2. Crack data of non-uniform structure with different grain orientations

[0120] like Figure 3 As shown, the non-uniform structure is also affected by the orientation. Similar to the results of the uniform structure, crack initiation always occurs in the crystal with a large Schmidt factor, or between grains with a large Schmidt factor difference. In addition, the cracks in the non-uniform structure under different orientations are consistent with the experimental crack phenomena, proving that the cohesive force model of the embodiment of the present invention can better predict the tensile cracks in the non-uniform structure. Figure 3 In the figure, the left side is the first orientation and the right side is the second orientation. The Schmidt factors corresponding to ①, ②, ③ and ④ on the left side are 0.4327, 0.4131, 0.3991 and 0.4375 respectively, and the Schmidt factors corresponding to ①, ②, ③ and ④ on the right side are 0.4318, 0.2456, 0.3894 and 0.3002 respectively.

[0121] 3. Analysis of crack results of non-uniform structure

[0122] like Figure 4 As shown in the figure, the inhomogeneous structure exhibits the characteristics of multiple cracks initiating and not being easily connected. In the inhomogeneous structure, the independent initiation of multiple cracks leads to the mutual influence of local stress fields. Compared with the initiation of a single crack, the initiation of multiple cracks can effectively absorb more external energy and improve the material's crack resistance. During the simulation, the high stress parts of the inhomogeneous structure are distributed in the fine-grained area. According to the Hall-Petch relationship: compared with coarse grains, fine grains have higher strength and are not easy to initiate cracks, which plays a role in resisting crack initiation. The coarse-grained part has more space and freedom within the crystal to generate and propagate dislocations, resulting in more slip systems being activated at the same time. This means that in coarse-grained materials, dislocations are more likely to start and continue to move, resulting in more plastic deformation. Compared with the uniform structure, in the inhomogeneous structure, during the loading process, large grains absorb part of the stress through plastic deformation, while small grains can resist the concentration of large stress due to their high strength, thereby alleviating the stress concentration of the overall material; large grains can withstand large plastic strains and provide strong deformation capacity, while the presence of small grains limits excessive plastic deformation, thereby reducing the accumulation of dislocations and the activation of slip systems. This structure allows large grains to bear most of the plastic deformation, while allowing small grains to improve the strength of the overall material by providing higher deformation resistance. This stress-strain distribution mechanism can reduce the excessive stress or strain generated at a single grain scale, effectively delay or inhibit the formation of cracks, and extend the service life of the material. While improving the strength of the material, the inhomogeneous structure also improves the ductility to a certain extent.

[0123] 4. Prediction of optimization direction of metal material microstructure

[0124] The synergistic effect between fine grains and coarse grains in the heterogeneous structure improves the strength and ductility of the material. Figure 4 It can be seen that cracks always expand in the fine-grained area first, and then expand into the coarse-grained area. When the crack enters the coarse-grained area from the fine-grained area, the grain size suddenly increases, the grain boundary density decreases, and the crack propagation path changes. This sudden change can easily lead to uneven distribution of stress concentration, and the crack may deflect or even branch during the expansion process. It can be inferred that the spatial arrangement and number of coarse-grained clusters with non-uniform structure under a certain volume will affect its performance, such as Figure 5 As shown in Figure 1, the irregular arrangement of coarse-grained clusters is likely to cause multiple deflections and branches of the crack path, absorb external energy, and reduce the failure rate of the material. Therefore, using this method to simulate the non-uniform structure of different spatial distributions of coarse-grained clusters can determine the direction for material microstructure optimization.

[0125] The metal material crack simulation method of the embodiment of the present invention embeds the cohesive force model and the crystal plasticity constitutive model into the microstructure finite element model of the metal material. After the finite element analysis, accurate stress-strain data and crack data can be obtained, thereby effectively restoring the tensile fracture behavior of the metal material and accurately predicting the tensile crack of the metal material. The method has the advantages of high precision, strong flexibility, the ability to evaluate the fracture behavior of the metal material, and intuitive display.

[0126] 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 cracks in metal materials, characterized in that: include: Acquire a cohesion model, and determine various undetermined parameters of the cohesion model; Acquiring a crystal plasticity constitutive model, and determining various undetermined parameters of the crystal plasticity constitutive model; Establishing a first microstructure finite element model of the metal material, and embedding the cohesive force model and the crystal plasticity constitutive model into the first microstructure finite element model; Applying a tensile load and boundary conditions to the first microstructure finite element model, and performing a finite element analysis to obtain a first finite element analysis result; The first finite element analysis result includes stress-strain data calculated based on the crystal plasticity constitutive model and crack data calculated based on the cohesive force model and the stress-strain data.

2. The metal material crack simulation method according to claim 1, characterized in that: The cohesion model includes: Where F is the traction force, k1 is the stiffness in the linear elastic stage, x is the displacement, x1 is the critical damage displacement, and F max is the critical damage stress, k2 is the slope of the traction force-displacement curve in the damage evolution stage, b is the intercept of the traction force-displacement curve in the damage evolution stage, x2 is the complete damage displacement, k1, x1, F max , k2, b and x2 are all unknown parameters.

3. The metal material crack simulation method according to claim 2, characterized in that: Determine the parameters to be determined of the cohesion model, specifically including: Conduct molecular dynamics simulation on metal materials to obtain the critical damage stress, critical damage displacement and complete damage displacement of metal materials; determining the stiffness of the linear elastic stage according to the critical damage stress and the critical damage displacement; The slope and intercept of the traction force-displacement curve in the damage evolution stage are determined according to the critical damage stress, the critical damage displacement and the complete damage displacement.

4. The metal material crack simulation method according to claim 2, characterized in that: The crystal plasticity constitutive model includes a kinematic model, a thermally activated flow law model and a kinematic hardening model.

5. The metal material crack simulation method according to claim 4, 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].

6. The metal material crack simulation method according to claim 5, characterized in that: The thermally activated flow law model includes: h αβ =h s [ω+(1-ω)δ αβ ] S sat =S0+S inc in, Plastic 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, g and q are 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, S inc is the sliding resistance added during the simulation; h s is the inherent hardening constant of metal materials, 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 slope coefficient of the size dependence and d is the size of the considered grain.< / z> < / z> 7. The metal material crack simulation method according to claim 6, characterized in that: The kinematic hardening model includes: Among them, r D is the dynamic restitution coefficient, 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, g, q, S0 * , k s , S inc 、h s 、r D 、h b * , k b All parameters are pending.

8. The metal material crack simulation method according to claim 7, characterized in that: Determine the parameters to be determined of the crystal plasticity constitutive model, specifically including: Establishing a second microstructure finite element model of the metal material, embedding the crystal plasticity constitutive model into the second microstructure finite element model, applying a tensile load and boundary conditions to the second microstructure finite element model, and performing finite element analysis to obtain a stress-strain curve of the microstructure finite element model; Conduct tensile tests on metal materials to obtain stress-strain curves of metal materials; The values ​​of the unknown parameters of the crystal plasticity constitutive model are adjusted so that the error between the stress-strain curve of the second microstructure finite element model and the stress-strain curve obtained by the tensile test is within a preset range, so as to determine the values ​​of the unknown parameters of the crystal plasticity constitutive model.

9. The metal material crack simulation method according to claim 1, characterized in that: Establishing a first microstructure finite element model of the metal material specifically includes: Acquiring microstructure data of the metal material; Establishing a geometric model based on the microstructure data; The geometric model is meshed and assigned material properties to obtain the first microstructure finite element model.

10. The metal material crack simulation method according to claim 1, characterized in that: The crack data includes the number of cracks and the location and size of each crack.

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