A method and system for crack tip opening angle prediction for ductile metal materials

Abstract

The application discloses a crack tip cracking prediction method and system for ductile metal materials, which can accurately characterize the strain energy density distribution of the crack tip of a ductile metal structure, and accurately and quantitatively characterize the crack initiation criterion verification and damage tolerance fatigue life prediction of the crack tip. The method comprises the following steps: obtaining the strain field of the crack tip of the ductile metal material to be measured based on DIC technology; constructing a constitutive model of the ductile metal material to be measured based on a uniaxial tensile test; calculating and obtaining the stress field of the crack tip of the ductile metal material to be measured according to the strain field and the constitutive model based on plastic deformation theory and Newton-Raphson iteration algorithm; calculating the elastic strain energy density field and the plastic strain energy density field of the crack tip of the ductile metal material to be measured according to the obtained stress field and strain field, and obtaining the critical plastic strain energy; and predicting the cracking of the crack tip of the ductile metal material to be measured according to the critical plastic strain energy.

Description

Technical Field

[0001] This invention belongs to the field of fracture behavior prediction technology for metallic materials, specifically relating to a method and system for predicting crack tip cracking in ductile metallic materials. Background Technology

[0002] Fracture prediction of metallic materials has significant guiding value for the design and application of engineering materials. Among fracture prediction methods, the strain energy density method is a very effective method for evaluating the static and fatigue fracture behavior of notched and unnotched components in engineering structures. Because it can simultaneously consider the effects of stress and strain on fracture, strain energy-based methods have begun to be studied and explored in depth.

[0003] Currently, methods for predicting crack tip initiation include: methods based on the application of strain energy density theory to predict the growth and propagation direction of complex cracks; or methods using models to predict the propagation of single and complex fatigue cracks; and the S-criterion proposed by Sih is applied to solve the crack initiation and propagation direction of circumferential cracks in T-bars and tubes under complex loading conditions.

[0004] However, due to the difficulty in characterizing the actual elastoplastic strain energy density distribution at the notch and crack tip, the analytical formulas for the elastic stress field at the crack tip in the linear elastic fracture mechanics framework cannot be directly applied to predict crack tip cracking in ductile metals, leading to significant errors. Furthermore, the theoretical solution for the HRR singular field (Hutchinson, Rice, Rosengren) at the crack tip in the elastoplastic fracture mechanics framework is very complex and difficult to apply quickly and conveniently in engineering practice. Therefore, there is currently no accurate method for characterizing the strain energy density distribution at the crack tip of ductile metal structures, and accurate fracture prediction for ductile metal structures is also impossible. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method and system for predicting crack tip initiation in ductile metal materials. It can accurately characterize the strain energy density distribution at the crack tip of ductile metal structural components and accurately quantitatively characterize the crack tip initiation criterion verification and fatigue life prediction of damage tolerance.

[0006] This invention is achieved through the following technical solution:

[0007] A method for predicting crack tip initiation in ductile metallic materials includes the following steps:

[0008] The strain field at the crack tip of the tough metallic material under test is obtained based on DIC technology;

[0009] A constitutive model of the toughness of the metal material under test was constructed based on uniaxial tensile tests.

[0010] Based on the theory of plastic deformation and the Newton-Raphson iterative algorithm, the stress field at the crack tip of the tough metallic material under test is calculated according to the strain field and constitutive model.

[0011] Based on the obtained stress and strain fields, the elastic strain energy density field and plastic strain energy density field at the crack tip of the tough metal material under test are calculated to obtain the critical plastic strain energy.

[0012] The cracking at the crack tip of the tough metallic material under test is predicted based on the critical plastic strain energy.

[0013] Preferably, the step of obtaining the strain field at the crack tip of the tough metallic material under test based on DIC technology specifically includes the following steps:

[0014] Prepare fracture mechanics specimens and perform surface treatment on the fracture mechanics specimens;

[0015] The fracture mechanics specimen was loaded onto the electronic universal tensile tester. After debugging the DIC test system, it was started, and the imaging device of the DIC test system was used to collect photographs of the fracture mechanics specimen.

[0016] The displacement and strain fields of fracture mechanics specimen photographs were calculated using the software processing device of the DIC test system.

[0017] Preferably, the preparation of the fracture mechanics specimen includes:

[0018] The specimens are prepared using a compact tensile test specimen or a three-point bend test specimen.

[0019] Preferably, the surface treatment of the fracture mechanics specimen includes:

[0020] The surface of the fracture mechanics specimen is uniformly sprayed with white paint for the DIC test;

[0021] The surface of the fracture mechanics specimen is uniformly sprayed with black speckles from the DIC test.

[0022] Preferably, the DIC test system includes the camera angle, the lamp illumination angle, and the distance between the camera and the fracture mechanics specimen.

[0023] Preferably, the constitutive model for constructing the toughness of the metallic material under test based on uniaxial tensile testing includes:

[0024] Stress-strain curves of tough metallic materials under test were obtained based on uniaxial tensile tests.

[0025] The Ramberg–Osgood model was used to fit the stress-strain curves to obtain relevant material parameter values.

[0026] Preferably, the stress-strain curve of the toughness-testing metallic material obtained based on the uniaxial tensile test includes:

[0027] Engineering stress-strain data and yield stress of the tough metallic material under test were collected by uniaxial tensile testing.

[0028] The stress-strain curve of the tough metallic material under test is obtained by converting the engineering stress-strain data. The conversion formula is as follows:

[0029] σ=s(1+e)

[0030] ε = ln(1 + e)

[0031] In the formula, s represents engineering stress, e represents engineering strain, σ represents equivalent stress, and ε represents equivalent strain.

[0032] Preferably, the model expression for the elastic strain energy density field is:

[0033]

[0034] In the formula, ω e Let E represent the elastic strain energy density field, and let σ represent the elastic modulus. e The stress is expressed as equivalent stress, ν represents Poisson's ratio, and σ represents the stress. x σ y Let τ be the normal stress in the plane. xy This is expressed as the shear stress in the plane.

[0035] Preferably, the model expression for the plastic strain energy density field is:

[0036]

[0037] In the formula, ω p Let σ represent the plastic strain energy density field, where α and n are constants related to the toughness of the metal material being tested, E represents the elastic modulus, and σ represents the plastic strain energy density field. e It is expressed as equivalent stress.

[0038] A crack tip propagation prediction system for ductile metallic materials includes:

[0039] The strain field acquisition module is used to acquire the strain field at the crack tip of the tough metal material under test based on DIC technology.

[0040] The constitutive model construction module is used to construct constitutive models of metallic materials with the required toughness based on uniaxial tensile tests.

[0041] The stress field calculation module is used to calculate the stress field at the crack tip of the tough metal material under test based on the plastic deformation theory and the Newton-Raphson iterative algorithm, according to the strain field and constitutive model.

[0042] The strain energy density field calculation module is used to calculate the elastic strain energy density field and plastic strain energy density field at the crack tip of the tough metal material under test based on the obtained stress field and strain field, and to obtain the critical plastic strain energy.

[0043] The crack prediction module is used to predict the cracking at the crack tip of the tough metal material under test based on the critical plastic strain energy.

[0044] Compared with the prior art, the present invention has the following beneficial technical effects:

[0045] This invention provides a method for predicting crack tip initiation in ductile metallic materials. Addressing the difficulty in quickly and accurately calculating the plastic strain energy density field at the crack tip in ductile metallic materials with existing cracks, this invention designs a method for dynamically solving the crack tip energy density distribution based on digital image correlation (DIC) testing technology. Specifically, it acquires the displacement and strain fields at the crack tip of the ductile metal using DIC testing technology. DIC testing technology can accurately capture the strain field at the crack tip of the ductile metallic sample surface from the start of cracking to fracture at different times, improving the accuracy of strain field calculation. Simultaneously… Constitutive models of the tough metallic materials under test are obtained through uniaxial tensile testing. Fitting these models improves the accuracy of data conversion in actual engineering projects, yielding more precise material-related constants. Furthermore, by combining plastic deformation theory and the Newton-Raphson iterative algorithm, the stress field at the crack tip of the tough metallic material is calculated. A MATLAB program is compiled and used to solve the nonlinear equations using the Newton-Raphson iterative algorithm, allowing the acquisition of the strain field in the crack tip region from the start of cracking to any point at fracture. Finally, the elastic strain energy density field and plastic strain energy density field are calculated by combining the stress and strain fields at the crack tip, thus obtaining the critical plastic strain energy as a crack initiation criterion. The crack tip initiation prediction method described in this invention can accurately characterize the elastoplastic stress field and elastoplastic strain energy density distribution at the crack tip of tough metal structural components, reduce the complexity of the strain energy density method, simplify the solution process, improve the solution accuracy and speed, and facilitate the use of the strain energy density method to guide the verification of crack tip initiation criteria and the quantitative characterization of damage tolerance in practical engineering applications. At the same time, it provides key basic data for predicting crack propagation, and can better guide the design of industrial structural component materials and the calculation of crack life. Attached Figure Description

[0046] Figure 1 This is a flowchart of the crack tip cracking prediction method of the present invention;

[0047] Figure 2This is a flowchart of the steps for solving the crack tip cracking criterion of the present invention;

[0048] Figure 3 This is a diagram showing the dimensions of the CT sample in an embodiment of the present invention;

[0049] Figure 4 The ε region of the 6092Al / SiCp composite material with 17.5% SiCp reinforcement in this embodiment of the invention is... y Schematic diagram of strain field;

[0050] Figure 5 This is a diagram showing the elastic strain energy density distribution in the crack tip region in an embodiment of the present invention;

[0051] Figure 6 This is a plastic strain energy density distribution diagram of the crack tip region in an embodiment of the present invention. Detailed Implementation

[0052] The principles and features of the present invention will be further described in detail below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clearly assist in illustrating the embodiments of the present invention.

[0053] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or it can be in a centered component. When a component is said to be "connected to" another component, it can be directly connected to the other component or it may also be in a centered component. When a component is said to be "set to" another component, it can be directly set on the other component or it may also be in a centered component.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0055] The present invention provides a method for predicting crack tip initiation in ductile metallic materials, such as... Figure 1 As shown, it includes the following steps:

[0056] The strain field at the crack tip of the tough metallic material under test is obtained based on DIC technology;

[0057] A constitutive model of the toughness of the metal material under test was constructed based on uniaxial tensile tests.

[0058] Based on the theory of plastic deformation and the Newton-Raphson iterative algorithm, the stress field at the crack tip of the tough metallic material under test is calculated according to the strain field and constitutive model.

[0059] Based on the obtained stress and strain fields, the elastic strain energy density field and plastic strain energy density field at the crack tip of the tough metal material under test are calculated to obtain the critical plastic strain energy.

[0060] The cracking at the crack tip of the tough metallic material under test is predicted based on the critical plastic strain energy.

[0061] This invention provides a method for predicting crack tip initiation in ductile metal materials. Addressing the difficulty in quickly and accurately calculating the plastic strain energy density field at the crack tip in ductile metal materials with existing cracks, this invention designs a method for dynamically solving the crack tip energy density distribution based on digital image correlation (DIC) testing technology. Specifically, it acquires the displacement and strain fields at the crack tip of the ductile metal using DIC testing technology. DIC testing technology can accurately capture the strain field at the crack tip of the ductile metal sample surface from the start of crack initiation to fracture at different times, improving the accuracy of strain field calculation. Simultaneously, a uniaxial tensile test is employed... The constitutive model of the tough metallic material to be tested is obtained through verification. Fitting the model can improve the accuracy of the conversion of actual engineering data and obtain more accurate material-related constants. Then, by combining the plastic deformation theory and the Newton-Raphson iterative algorithm, the stress field at the crack tip of the tough metallic material is calculated. After compiling and calculating the Newton-Raphson iterative solution of the nonlinear equation system in MATLAB, the strain field of the crack tip region from the start to any time of fracture can be obtained. Finally, the elastic strain energy density field and the plastic strain energy density field are calculated by combining the stress field and strain field at the crack tip, so as to obtain the critical plastic strain energy for predicting the crack initiation at the crack tip of the tough metallic material.

[0062] The crack tip initiation prediction method described in this invention can accurately characterize the elastoplastic stress field and elastoplastic strain energy density distribution at the crack tip of tough metal structural components. It reduces the complexity of solving the strain energy density method, simplifies the solution process, and improves the accuracy and speed of the solution. It facilitates the use of the strain energy density method to guide the verification of crack tip initiation criteria and the quantitative characterization of damage tolerance in practical engineering applications. It can accurately calculate the energy density distribution at the crack tip, and thus be applied to the calculation of damage tolerance of key structural components in industries such as military. At the same time, it provides key basic data for predicting crack propagation, and can guide the design and crack calculation of industrial structural component materials, and better provide key data for the research and development of materials such as aerospace materials and petroleum equipment materials.

[0063] like Figure 2 As shown, the specific steps of the crack tip cracking prediction method of the present invention are as follows:

[0064] Step 1: Obtain the strain field at the crack tip using DIC (Digital Image Correlation) testing of the crack propagation specimen;

[0065] ① To prepare fracture mechanics specimens, compact tensile specimens (CT specimens) or three-point bending specimens can be used.

[0066] ② Spray white paint specifically for DIC testing evenly onto the sample surface to coat the sample surface with a uniform layer of white paint;

[0067] ③ Spray the DIC test-specific black speckle evenly onto the sample surface;

[0068] ④ Clamp the sample on the electronic universal tensile testing machine so that the sprayed speckled side can be photographed from the front by the camera of the DIC testing system;

[0069] ⑤ Adjust the camera angle, lamp illumination angle, and distance between the camera and the sample of the DIC test system to be at their optimal state;

[0070] ⑥ Start the DIC test imaging system and acquire multiple speckle photos (20 in this embodiment). Use the DIC test software processing system to calculate the displacement field and strain field of the multiple static speckle photos. If the displacement field and strain field can be calculated and the strain cloud map has no voids, dynamic photo acquisition can continue.

[0071] ⑦ Simultaneously activate the DIC test imaging system and the electronic universal tensile tester to obtain all photographs of the fracture mechanics specimen from the start of loading to the final fracture.

[0072] ⑧ The software processing system of DIC test is used to calculate the strain field at the crack tip of the specimen surface from the start to the fracture at different times, and output the data.

[0073] Step 2: Uniaxial tensile test;

[0074] 1) Prepare uniaxial tensile specimens (plate or rod) of the toughness metal material to be tested according to GB / T 228, and conduct uniaxial tensile tests to obtain engineering stress-strain data and yield stress σ0.

[0075] 2) The stress-strain curve of the uniform deformation stage is converted using the following formula:

[0076] σ=s(1+e)

[0077] ε = ln(1 + e)

[0078] Where s represents engineering stress, e represents engineering strain, σ represents equivalent stress, and ε represents equivalent strain, the elastic modulus E is first obtained by linear fitting of the elastic stage, and then the solution is performed. Then, ε-ε0 / E is used to process the data of the entire curve points to obtain ε.p Finally, regarding σ and ε p The data utilizes the Ramberg–Osgood model The fitting process is performed to obtain the values ​​of α and n, where α and n represent constants related to the toughness of the metal material being tested.

[0079] Step 3: Calculate the elastoplastic stress field;

[0080] 1) The nonlinear equations relating the strain field and the strain field under plane stress conditions are as follows:

[0081]

[0082] In the formula, ε x ε y Let σ represent the normal strain of the plane, γ represent the shear strain of the plane, ν represent Poisson's ratio, and σ represent the normal strain of the plane. e It is expressed as equivalent stress.

[0083] Among them, stress component s x and s y for:

[0084]

[0085]

[0086] Where, σ x σ y Let τ be the normal stress in the plane. xy This is expressed as the shear stress in the plane.

[0087] Wherein, the equivalent stress σ e Expressed as:

[0088]

[0089] 2) Compile a MATLAB program for solving nonlinear equations using the Newton-Raphson iterative method;

[0090] 3) The input data is the strain field (ε) at the crack tip region from the start of the fracture mechanics test to any moment of fracture. x , ε y and γ).

[0091] 4) The stress field (σ) in the crack tip region was obtained by calculating the nonlinear equations using the MATLAB program Newton-Raphson iterative solution. x , σ y and τ xy ).

[0092] Step 4: Calculate the elastic and plastic strain energy density fields;

[0093] After obtaining the stress and strain field at the crack tip region of a ductile metal fracture mechanics specimen at a certain moment of loading, the strain field (ε) is... x , ε y and γ) and stress field (σ) x , σ y and τ xy Substituting into the following formula, the elastic strain energy density can be obtained:

[0094]

[0095] strain field (ε) x , ε y and γ) and stress field (σ) x , σ y and τ xy Substituting into the following formula, the plastic strain energy density can be obtained.

[0096]

[0097] In the formula, ω e Represented as the elastic strain energy density field, ω p It is represented as the plastic strain energy density field.

[0098] Step 5: Calculate the critical plastic strain energy;

[0099] After obtaining the plastic strain energy density field of the crack tip region at a certain moment of loading of the ductile metal fracture mechanics specimen, the plastic strain energy of the entire strain field calculation region at the crack tip is obtained by discrete summation. The calculation method is as follows:

[0100]

[0101] In the formula, W p ω represents the plastic strain energy of the entire strain field calculation region at a certain moment. pi denoted as the plastic strain energy density at the smallest unit of the DIC method in different regions at a certain moment, v represents the volume at the smallest unit, and the thickness direction can be set to unit length.

[0102] The critical plastic strain energy density at fracture can be calculated using the above formula.

[0103] The criterion for crack tip initiation in ductile materials can be determined by the plastic strain energy W. p Has it been achieved? Make judgments and predictions when W p achieve When the crack tip cracks, the crack will open. This invention provides a quantitative characterization as a basis for judging the crack tip cracking, and makes predictions and takes corresponding measures in advance based on this.

[0104] This invention also provides a crack tip cracking prediction system for ductile metallic materials, used to implement the crack tip cracking prediction method described in this invention, comprising:

[0105] The strain field acquisition module is used to acquire the strain field at the crack tip of the tough metal material under test based on DIC technology.

[0106] The constitutive model construction module is used to construct constitutive models of metallic materials with the required toughness based on uniaxial tensile tests.

[0107] The stress field calculation module is used to calculate the stress field at the crack tip of the tough metal material under test based on the plastic deformation theory and the Newton-Raphson iterative algorithm, according to the strain field and constitutive model.

[0108] The strain energy density field calculation module is used to calculate the elastic strain energy density field and plastic strain energy density field at the crack tip of the tough metal material under test based on the obtained stress field and strain field, and to obtain the critical plastic strain energy.

[0109] The crack prediction module is used to predict the cracking at the crack tip of the tough metal material under test based on the critical plastic strain energy.

[0110] Example

[0111] This embodiment uses 6092Al / SiCp, a SiCp-reinforced 6092 aluminum matrix composite material with a particle volume fraction of 17.5%, as the implementation object. The determination process includes the following steps:

[0112] 1. DIC loading test of CT specimens

[0113] Take CT specimens (e.g.) Figure 3 As shown, loading tests were conducted on the CT specimens, and images of the loading process were acquired using the Vic-3D (Correlatedsolution) DIC testing system. Based on the acquired images of the CT specimens from the start of loading to before fracture, the Vic-3D software system was used to process the acquired images and obtain the ε at the crack tip. x , ε y and γ strain field, where ε is at the moment before the CT specimen fractures. y strain field such as Figure 4 As shown.

[0114] 2. Uniaxial tensile test

[0115] Uniaxial tensile specimens of 6092Al / SiCp, a 17.5% SiCp-reinforced 6092 aluminum matrix composite, were prepared and subjected to uniaxial tensile tests on an electronic universal tensile testing machine. The linear elastic phase of the stress-strain curves was fitted, yielding an elastic modulus of 69500 ​​MPa. The yield stress was 382 MPa, and ε0 was 0.0041. True stress and plastic strain curves were obtained using the Ramberg–Osgood model. The true stress and plastic strain curves were fitted, with a fitting α of 0.649 and n of 22.59.

[0116] 3. Calculate the elastoplastic stress field

[0117] 1) Compile a MATLAB program for solving nonlinear equations using the Newton-Raphson iterative method;

[0118] 2) The stress components (σ) under plane stress conditions in the nonlinear equation system x , σ y and τ xy ) and strain component (ε x , ε y Substitute the relationship between γ and γ into the MATLAB program;

[0119]

[0120] 3) Inputting the strain components (ε) at the crack tip region of the 6092Al / SiCp composite material reinforced with 17.5% SiCp into the MATLAB program. x , ε y and γ);

[0121] 4) The stress field (σ) at the crack tip region of the 17.5% SiCp-reinforced 6092 aluminum matrix composite 6092Al / SiCp was calculated using MATLAB. x , σ y and τ xy ).

[0122] 4. Calculate the elastic strain energy density and plastic strain energy density at the crack tip.

[0123] 1) Substitute the strain and stress components of the crack tip region of the 17.5% SiCp-reinforced 6092 aluminum matrix composite 6092Al / SiCp into the following formula to obtain the elastic strain energy density distribution in the crack tip region, such as... Figure 5 As shown.

[0124]

[0125] 2) Substitute the strain and stress components of the crack tip region of the 17.5% SiCp-reinforced 6092 aluminum matrix composite 6092Al / SiCp into the following formula to obtain the plastic strain energy density distribution in the crack tip region, such as... Figure 6 As shown.

[0126]

[0127] 5. Calculate the critical plastic strain energy

[0128] Substituting the plastic strain energy density field of the crack tip region before fracture in the 17.5% SiCp-reinforced 6092 aluminum matrix composite 6092Al / SiCp into the following formula, the critical plastic strain energy is obtained.

[0129]

[0130] The critical plastic strain energy of the crack tip region of the 6092Al / SiCp aluminum matrix composite material with 17.5% SiCp reinforcement at the fracture time was calculated to be 0.038 J.

[0131] Based on the critical plastic strain energy of the crack tip region of the 17.5% SiCp-reinforced 6092 aluminum matrix composite 6092Al / SiCp, the fracture behavior of the 17.5% SiCp-reinforced 6092 aluminum matrix composite 6092Al / SiCp was predicted. Fracture would occur when the plastic strain energy in a certain region reached 0.038J.

[0132] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for predicting crack tip opening of a ductile metal material, characterized by, Includes the following steps: The strain field at the crack tip of the tough metallic material under test is obtained based on DIC technology; A constitutive model of the toughness of the metal material under test was constructed based on uniaxial tensile tests. Based on the theory of plastic deformation and the Newton-Raphson iterative algorithm, the stress field at the crack tip of the tough metallic material under test is calculated according to the strain field and constitutive model. Based on the obtained stress and strain fields, the elastic strain energy density field and plastic strain energy density field at the crack tip of the tough metal material under test are calculated to obtain the critical plastic strain energy. The cracking at the crack tip of the tough metallic material under test is predicted based on the critical plastic strain energy. The constitutive model for constructing the toughness of the metallic material under test based on uniaxial tensile testing includes: Stress-strain curves of tough metallic materials under test were obtained based on uniaxial tensile tests. The stress-strain curves of the tough metallic material to be tested, obtained based on uniaxial tensile testing, include: Engineering stress-strain data and yield stress of the tough metallic material under test were collected by uniaxial tensile testing. The stress-strain curve of the tough metallic material under test is obtained by converting the engineering stress-strain data. The conversion formula is as follows: In the formula, Represented as engineering stress, Represented as engineering strain, Expressed as equivalent stress, Expressed as equivalent strain; The model expression for the plastic strain energy density field is as follows: In the formula, Represented as the plastic strain energy density field, Expressed as the elastic modulus, Represented as equivalent stress; First, a linear fit is performed on the elastic phase to obtain the elastic modulus. Solve Then adopt The data from the entire curve points is processed to obtain Finally, for and The data utilizes the Ramberg–Osgood model ( To perform fitting and obtain and value.

2. The method for predicting crack tip initiation in ductile metallic materials according to claim 1, characterized in that, The method for obtaining the strain field at the crack tip of the tough metallic material under test based on DIC technology specifically includes the following steps: Prepare fracture mechanics specimens and perform surface treatment on the fracture mechanics specimens; The fracture mechanics specimen was loaded onto the electronic universal tensile tester. After debugging the DIC test system, it was started, and the imaging device of the DIC test system was used to collect photographs of the fracture mechanics specimen. The displacement and strain fields of fracture mechanics specimen photographs were calculated using the software processing device of the DIC test system.

3. The method for predicting crack tip initiation in ductile metallic materials according to claim 2, characterized in that, The preparation of the fracture mechanics specimen includes: The specimens are prepared using a compact tensile test specimen or a three-point bend test specimen.

4. The method for predicting crack tip opening displacement of a ductile metal material according to claim 2, wherein The surface treatment of the fracture mechanics specimen includes: The surface of the fracture mechanics specimen is uniformly sprayed with white paint for the DIC test; The surface of the fracture mechanics specimen is uniformly sprayed with black speckles from the DIC test.

5. The method for predicting crack tip opening displacement of a ductile metal material according to claim 2, wherein The DIC test system includes the camera angle, lamp illumination angle, and distance between the camera and the fracture mechanics specimen.

6. The method for predicting crack tip opening displacement of a ductile metal material according to Claim 1, wherein The model expression for the elastic strain energy density field is: In the formula, Represented as the elastic strain energy density field, Expressed as the elastic modulus, Expressed as equivalent stress, Expressed as Poisson's ratio, , These are respectively represented as the normal stresses of the plane. This is expressed as the shear stress in the plane.

7. A crack tip initiation prediction system for ductile metallic materials, characterized in that, The crack tip cracking prediction method based on any one of claims 1-6 includes: The strain field acquisition module is used to acquire the strain field at the crack tip of the tough metal material under test based on DIC technology. The constitutive model construction module is used to construct constitutive models of metallic materials with the required toughness based on uniaxial tensile tests. The stress field calculation module is used to calculate the stress field at the crack tip of the tough metal material under test based on the plastic deformation theory and the Newton-Raphson iterative algorithm, according to the strain field and constitutive model. The strain energy density field calculation module is used to calculate the elastic strain energy density field and plastic strain energy density field at the crack tip of the tough metal material under test based on the obtained stress field and strain field, and to obtain the critical plastic strain energy. The crack prediction module is used to predict the cracking at the crack tip of the tough metal material under test based on the critical plastic strain energy.

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