A hydrogen induced cracking molecular dynamics-cohesion multiscale simulation method

Abstract

The application discloses a hydrogen-induced cracking molecular dynamics-cohesion cross-scale simulation method, comprising the following steps: constructing a geometric model reflecting the actual microstructure of a material based on the multi-scale structure characteristics such as grain size and grain boundary angle obtained through metallographic observation and electron backscatter diffraction experiments; simulating the fracture process of a micro-interface under different hydrogen concentrations through a molecular dynamics method, obtaining traction-separation data, and calibrating the core parameters of a cohesion model; embedding the above parameters into a polycrystalline finite element model constructed based on a tessellation polygon, realizing parameter transmission and coupled calculation from a micro-scale to a meso-scale; and accurately describing hydrogen-induced grain boundary damage and crack propagation behavior through a cohesion element. The method significantly improves the reliability and prediction accuracy of the model through multi-scale correlation modeling and direct parameter calibration, and provides a theoretical basis and an engineering applicable tool for hydrogen-induced cracking resistance design and life assessment of equipment materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of finite element numerical simulation of hydrogen-induced crack propagation of metal materials, and particularly relates to a molecular dynamics-cohesive force cross-scale simulation method for hydrogen-induced cracking. BACKGROUND

[0002] As a core clean energy carrier to achieve the goal of carbon neutrality, hydrogen energy has the dual advantages of high energy density and zero carbon emission, and has become the core direction of global energy transformation. Its combustion product is only water, which has significantly lower environmental load than fossil energy, and has the advantage of being renewable, and has irreplaceable value for building a sustainable energy system. The large-scale application of hydrogen energy is highly dependent on safe and efficient transportation technology, and hydrogen-doped natural gas pipelines become the most economical solution because they can reuse existing infrastructure. This practical demand makes it necessary to deeply study the behavior mechanism of materials in a hydrogen environment, especially the interaction mechanism of hydrogen and metal materials, which is a key scientific and technological proposition to ensure the safety of energy transportation.

[0003] Hydrogen embrittlement seriously restricts the engineering application of hydrogen-doped pipelines. Hydrogen embrittlement refers to the phenomenon that the toughness of the material suddenly decreases after hydrogen penetrates into the metal lattice, causing unpredictable brittle fracture of the pipeline under service stress, which directly threatens the reliability of the energy transportation system. Hydrogen-induced cracking behavior has typical multi-scale characteristics, which originates from the nucleation of micro-cracks caused by the interaction of hydrogen atoms and crystal defects at the microscale, then the cracks propagate along the grain boundary network at the mesoscale, and finally burst into brittle fracture at the macroscale. Due to the hysteresis of hydrogen diffusion and the instantaneous nature of crack propagation, traditional single-scale simulation methods have inherent limitations. Molecular dynamics can reveal the microscale hydrogen-defect interaction, but cannot capture the mesoscale crack propagation dynamics. The cohesive force model can describe the mesoscale crack propagation, but lacks constitutive parameters derived from atomic mechanisms. Existing technologies fail to establish a parameter transfer path across micro-mesoscale, resulting in a disconnection between micro hydrogen aggregation mechanism and mesoscale crack propagation behavior. Therefore, it is urgent to develop a cross-scale simulation method that combines micro-mechanism and meso-evolution, which can accurately analyze the whole process of hydrogen-induced cracking from microscale to mesoscale by coupling molecular dynamics and cohesive force model, and further understand the mechanism of hydrogen-induced crack propagation of metals. SUMMARY

[0004] To solve the above technical problems, the present application provides a molecular dynamics-cohesive force cross-scale simulation method for hydrogen-induced cracking, which is used for simulating and analyzing the microscale and mesoscale mechanism of hydrogen-induced cracking behavior of metal materials in a hydrogen environment.

[0005] The present application is implemented by using the following technical solutions:

[0006] A molecular dynamics-cohesive force cross-scale simulation method for hydrogen-induced cracking, comprising the following steps:

[0007] Step S1: Conduct metallographic observation experiments on metallic materials to obtain the grain characteristic distribution of metallic materials;

[0008] Step S2: Conduct electron backscatter diffraction microscopic characterization experiments on metallic materials to obtain the grain boundary angle distribution and grain size distribution of metallic materials;

[0009] Step S3: Based on the grain feature distribution obtained in step S1 and the grain boundary angle distribution obtained in step S2, construct a molecular dynamics interface model containing initial cracks and hydrogen atoms.

[0010] Step S4: Perform displacement loading and tensile simulation on the molecular dynamics grain boundary model constructed in step S3 to obtain stress-strain data and traction-separation data of the crack propagation process, and fit the parameters of the cohesive constitutive model.

[0011] Step S5: Based on the grain size distribution obtained in step S2, a polycrystalline geometric model is generated using the Thiessen polygon algorithm, and a compact tensile specimen model is established on the periphery, which are then combined into a finite element model based on grain boundaries.

[0012] Step S6: Embed zero-thickness cohesive units at the grain boundaries of the polycrystalline geometric model obtained in step S5, and assign the parameters of the cohesive constitutive model fitted in step S4 to the zero-thickness cohesive units.

[0013] Step S7: Perform finite element simulation based on grain boundary cohesion model under hydrogen-exposed environment, analyze hydrogen-induced crack propagation behavior of different microstructures, and obtain support reaction force-strain data and crack propagation path data.

[0014] Specifically, step S1 includes: preparing the metal material into a test sample according to the sample preparation requirements of the metallographic microscope, and obtaining the grain characteristic distribution data of the metal material through metallographic observation.

[0015] Specifically, step S2 includes:

[0016] Based on the surface condition requirements of the electron backscatter diffractometer, the metallic material is prepared as the test sample;

[0017] The microstructure of metallic materials is characterized by scanning electron microscopy, and the observation data is analyzed and processed using analysis software to obtain crystal characteristic parameters.

[0018] Specifically, step S3 includes: constructing an interface calculation model based on the grain feature distribution and grain boundary angle distribution data according to the structural requirements of the atomic model in molecular dynamics simulation, and obtaining a defect-containing hydrogen-induced crack evolution model by implanting initial cracks and hydrogen atoms.

[0019] Specifically, step S4 includes: applying displacement boundary conditions to the hydrogen-induced crack evolution model according to the technical requirements of the loading process in molecular dynamics simulation, simulating crack propagation behavior through the tensile process, extracting stress-strain data and traction-separation data of the grain boundary region, and obtaining cohesive constitutive model parameters based on bilinear fitting.

[0020] Specifically, the stress-strain data and traction-separation data include one or more of the following: stress-strain curves, stress contour maps, and interfacial tension separation displacement curves; the cohesive constitutive model parameters include critical interfacial tension, initial damage displacement, critical damage displacement, stiffness, and critical fracture energy.

[0021] Specifically, the generation of the polycrystalline geometric model in step S5 is based on the requirements of the cohesive force model for the geometric modeling of polycrystalline structures.

[0022] Specifically, the constitutive model of the cohesive unit in step S6 includes:

[0023] Elastic phase ( ):

[0024] ;

[0025] in, For traction force; For stiffness; This represents the damage displacement;

[0026] Damage stage ( ):

[0027] ;

[0028] ;

[0029] ;

[0030] ;

[0031] in, The damage factor for the cohesive unit; This represents the maximum damage displacement; This represents the maximum equivalent damage displacement under the mixed cracking mode; This is the critical damage displacement; This represents the normal damage displacement; This represents the tangential damage displacement.

[0032] Free surface ( ):

[0033] .

[0034] Specifically, the characteristics of different microstructures in step S7 include one or more of the following: grain boundary angle and grain size; the support reaction force-strain data and crack propagation path data include one or more of the following: support reaction force-strain curve, crack initiation location, crack initiation time, crack propagation path, and crack propagation rate.

[0035] The beneficial effects of this invention are as follows:

[0036] (1) By integrating microscopic characterization data with cross-scale parameter transfer mechanisms, the entire process of hydrogen-induced cracking behavior of metallic materials from microscopic damage to mesoscopic expansion was accurately analyzed.

[0037] (2) Based on the microstructure characteristics obtained by metallographic observation and electron backscatter diffraction, a molecular dynamics interface model of real material response is constructed to accurately capture the aggregation behavior of hydrogen atoms at the grain boundary and the damage evolution law. The micro-interface mechanical behavior output by molecular dynamics is transformed into cohesive constitutive model parameters through bilinear functions, completely avoiding the distortion of physical mechanism caused by empirical assumptions. Combined with the polycrystalline geometric model that matches the generated Thiessen polygons with the measured grain size distribution, parameterized cohesive units are embedded at the grain boundary to achieve high-precision simulation of crack propagation path and rate along the grain.

[0038] (3) A non-destructive transmission chain of “real experimental data → microscale mechanism → microscale failure behavior” has been established, which can quantitatively analyze the coupling effect of hydrogen concentration, microstructure and crack propagation, and provide a decision-making basis with both theoretical rigor and engineering practicality for the hydrogen embrittlement resistance design and safety assessment of hydrogen-contaminated equipment. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0040] Figure 1 This is a flowchart of the molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking of the present invention.

[0041] Figure 2 These are microstructure images of the weld zone and heat-affected zone in this embodiment;

[0042] Figure 3 This is a statistical diagram of the angular grain boundary distribution and grain size in the weld zone of the X80 pipe in this embodiment;

[0043] Figure 4This is a diagram of the Bagaryatskii orientation relationship ferrite-cementite two-phase interface model in this embodiment;

[0044] Figure 5 This is a stress-strain curve diagram of the ferrite-cementite two-phase interface model under different hydrogen concentrations in this embodiment.

[0045] Figure 6 This is a traction-separation curve of the ferrite-cementite two-phase interface model with a 0.5% hydrogen concentration in this embodiment;

[0046] Figure 7 This is a schematic diagram of the bilinear cohesive constitutive model in this embodiment;

[0047] Figure 8 This is a schematic diagram of the polycrystalline finite element model in this embodiment;

[0048] Figure 9 The support reaction force-strain curves and critical stress intensity factor curves for different grain sizes are shown in this embodiment.

[0049] Figure 10 The images show crack propagation diagrams for polycrystalline models with 1μm and 3μm grain sizes in this embodiment. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0051] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0052] The following is in conjunction with the appendix Figures 1-10 The following describes some embodiments of the present invention in detail. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0053] This invention proposes a molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking. In a preferred embodiment, this method is as follows: Figure 1 As shown, it includes the following steps:

[0054] Step S1: Conduct metallographic observation experiments on metallic materials to obtain the grain characteristic distribution of metallic materials;

[0055] Step S2: Conduct electron backscatter diffraction microscopic characterization experiments on metallic materials to obtain the grain boundary angle distribution and grain size distribution of metallic materials;

[0056] Step S3: Based on the grain feature distribution obtained in step S1 and the grain boundary angle distribution obtained in step S2, construct a molecular dynamics interface model containing initial cracks and hydrogen atoms.

[0057] Step S4: Perform displacement loading and tensile simulation on the molecular dynamics grain boundary model constructed in step S3 to obtain stress-strain data and traction-separation data of the crack propagation process, and fit the parameters of the cohesive constitutive model.

[0058] Step S5: Based on the grain size distribution obtained in step S2, a polycrystalline geometric model is generated using the Thiessen polygon algorithm, and a compact tensile specimen model is established on the periphery, which are then combined into a finite element model based on grain boundaries.

[0059] Step S6: Embed zero-thickness cohesive units at the grain boundaries of the polycrystalline geometric model obtained in step S5, and assign the parameters of the cohesive constitutive model fitted in step S4 to the zero-thickness cohesive units.

[0060] Step S7: Perform finite element simulation based on grain boundary cohesion model under hydrogen-exposed environment, analyze hydrogen-induced crack propagation behavior of different microstructures, and obtain support reaction force-strain data and crack propagation path data.

[0061] The following section describes the detailed technical solutions and implementation of each step of this method, using specific data and examples:

[0062] Step S1: Conduct metallographic observation tests on the metallic material to obtain the grain characteristic distribution: In this embodiment, the grain characteristic distribution of the metallic material is obtained through metallographic observation tests. According to the sample preparation requirements for metallographic microscopy, a cuboid sample containing the weld zone, heat-affected zone, and base material zone is cut along the axial direction of the X80 pipeline, with dimensions of 30 mm × 10 mm × 10 mm. The observation surface of the sample is sequentially polished with sandpaper until the surface is free of scratches. Then, it is etched with a 4% nitric acid alcohol solution to expose the microstructure. The types and distribution of microstructures in each region of the X80 pipeline steel ring weld are obtained as follows: Figure 2 As shown.

[0063] Step S2: Conduct electron backscattering diffraction microscopic characterization experiments on metallic materials to obtain microstructural characteristics: In this embodiment, the microstructural characteristics of metallic materials are obtained through electron backscattering diffraction microscopic characterization experiments. According to the sample preparation requirements of electron backscattering diffraction experiments, cubic samples of 10mm×10mm×10mm are cut along the X80 pipe for the weld zone, heat-affected zone, and base material zone respectively. The observation surfaces of the samples are mechanically polished step by step with sandpaper until the surface is free of scratches. A polishing solution is prepared and electrolytically polished on the observation surfaces. The polishing solution consists of 665ml acetic acid + 35ml deionized water + 125ml chromic acid. The polishing voltage is set to 16V, and polishing is performed for 10min. The polished sample is placed in the scanning electron microscope sample chamber, and the scanning step size is set to 1μm and the scanning range is 500μm×500μm. Electron backscattering diffraction data of the weld zone, heat-affected zone, and base material zone are collected. The microstructure of metallic materials was observed using a scanning electron microscope equipped with EBSD, and the observation data was analyzed and processed using the OIM Analysis software to obtain, for example... Figure 3 (a) shows the grain boundary angle distribution diagram and as shown in the figure. Figure 3 (b) shows the grain size distribution diagram.

[0064] Step S3: Constructing a molecular dynamics interface model with an initial crack: In this embodiment, based on the obtained microstructure types and grain boundary angle distribution of the metallic material, two types of molecular dynamics interface models were established using Atomsk modeling software: a Bagaryatskii orientation relationship ferrite-cementite two-phase interface model and a ferrite-ferrite symmetric tilted grain boundary model with different grain boundary angles. A 40Å × 10Å rectangular initial crack was set at the center of the grain boundary cohesive region, and hydrogen atoms were implanted at a ratio of grain boundary region: non-grain boundary region = 4:1, with hydrogen concentration gradients set to 0.5%, 1%, and 2%. The Bagaryatskii orientation relationship ferrite-cementite two-phase interface model is shown below. Figure 4 As shown.

[0065] Step S4: Perform displacement loading and tensile simulation of the molecular dynamics interface model to obtain stress-strain and traction-separation data during crack propagation. Fit the parameters of the cohesive constitutive model to minimize the energy of the constructed molecular dynamics interface model containing the initial crack and hydrogen atoms. Optimize the atomic positions using the conjugate gradient method. Then, relax the system for 50 ps in a 300 K isothermal environment under the NPT ensemble to reach equilibrium. Switch to the NVT ensemble, fix 5 Å thick atomic layers at the top and bottom of the model as loading boundaries, and apply a reverse displacement load to achieve uniaxial tension. Control the strain rate to 1 × 10⁻⁶. 9s⁻¹, continuously loaded for 20 ps until the model fractured. Stress-strain data, atomic force and displacement data of the grain boundary cohesive region were recorded using LAMMPS software, and stress-strain data and traction separation data of different hydrogen concentrations and different micro-interface models were analyzed.

[0066] The specific analysis includes:

[0067] (1) Stress-strain curve analysis of ferrite-cementite two-phase interface model under different hydrogen concentrations

[0068] like Figure 5 As shown, it displays the stress-strain curves of the ferrite-cementite interface model under different hydrogen concentrations. Analysis reveals that all curves sequentially undergo three stages: elastic deformation, plastic deformation, and fracture. Figure 5 (a) It can be seen that the introduction of hydrogen atoms reduces the peak stress of the ferrite-cementite grain boundary model from 11.007 GPa to 10.478 GPa, a decrease of 4.81%. Furthermore, the hydrogen-containing grain boundary model begins to enter the plastic deformation stage at a strain of 0.045, at which point slip occurs at the grain boundaries accompanied by a phase transformation; while the hydrogen-free grain boundary model only enters plastic deformation at a strain of 0.049. Compared to the hydrogen-containing model, the initial plastic strain is increased by 8.89%. Figure 5 (b) It can be seen that with the increase of hydrogen atom concentration in the grain boundary model, the peak stress, plastic initiation strain, and fracture initiation strain all show a decreasing trend, but the magnitude of the decrease is different. The results indicate that the presence of hydrogen atoms reduces the damage resistance of the grain boundary, causing it to be damaged at lower stresses, thereby further weakening the load-bearing capacity of the grain boundary.

[0069] (2) Analysis of traction-separation curves of ferrite-cementite two-phase interface model under different hydrogen concentrations

[0070] like Figure 6 As shown, the traction-separation curves of the ferrite-cementite two-phase interface model at a hydrogen concentration of 0.5% are displayed. Data points represent simulation results, curves are fitted curves, and pentagrams indicate the endpoints of bilinear fitting. Bilinear fitting was performed on the traction-separation curves at different hydrogen concentrations, and the parameters of the cohesive constitutive model are shown in Table 1. Table 1 shows that the introduction of hydrogen atoms leads to a decrease in the critical interfacial tension, critical damage displacement, and critical fracture energy of the grain boundary model. With increasing hydrogen concentration, the tension at the crack interface gradually weakens, and the model's deformation capacity significantly degrades. This result confirms the characteristic that metallic materials are more prone to brittle fracture in hydrogen environments.

[0071] The parameters of the cohesive constitutive model include: the critical interfacial tension obtained through bilinear fitting. Initial damage displacement Critical damage displacement The stiffness was calculated based on the above parameters. Critical fracture energy ;

[0072] in, ; .

[0073] Table 1. Parameters of the bilinear cohesive constitutive model

[0074]

[0075] Step S5: Constructing a polycrystalline geometric model based on the Thiessen polygon algorithm. Prior to this implementation, a polycrystalline geometric model is constructed using the Thiessen polygon algorithm. Based on the grain size distribution data obtained in step S2, characteristic grain sizes are extracted from the weld zone, heat-affected zone, and base metal zone. A Python program is written based on the Thiessen polygon algorithm, and this script is executed by calling the Abaqus Python interface, thereby generating a Thiessen polygon geometric model conforming to the aforementioned characteristic grain sizes in the Abaqus environment. The model size is set to 60 μm × 7.5 μm, and the grain boundary thickness is set to 0 to meet the embedding requirements of zero-thickness cohesive elements. Subsequently, a compact tensile specimen model of the grain periphery is established according to the standard ASTM E399, with dimensions of 150 μm in length, 144 μm in width, and a circular hole diameter of 30 μm. This compact tensile specimen model is then merged with the Thiessen polygon geometric model to finally form a complete model that can be used for crystal finite element analysis.

[0076] Step S6: Embed zero-thickness cohesive units at the grain boundaries of the polycrystalline model. Based on the cohesive constitutive model parameters obtained from molecular dynamics simulations, considering the influence of hydrogen concentration, zero-thickness cohesive units are embedded at the grain boundary positions of the polycrystalline geometry, and the cohesive constitutive model parameters are assigned to the cohesive units. In this embodiment, the following is selected: Figure 7 The bilinear cohesive constitutive model shown is used to describe the hydrogen-induced damage and cracking behavior of grain boundaries in metallic materials under hydrogen-exposed environments. This constitutive model divides grain boundary damage into three stages: elastic stage, damage stage, and free surface stage. The constitutive relations of each stage are shown in the following equations:

[0077] Elastic phase ( ):

[0078] ;

[0079] in, For traction force; For stiffness; This represents the damage displacement;

[0080] Damage stage ( ):

[0081] ;

[0082] ;

[0083] ;

[0084] ;

[0085] in, The damage factor for the cohesive unit; This represents the maximum damage displacement; This represents the maximum equivalent damage displacement under the mixed cracking mode; This is the critical damage displacement; This represents the normal damage displacement; This represents the tangential damage displacement.

[0086] Free surface ( ):

[0087] .

[0088] In this embodiment, the maximum nominal stress criterion is selected as the damage initiation criterion for the cohesive element:

[0089] .

[0090] In the formula: This is the normal stress value; This represents the maximum normal stress value. The shear stress is in the first direction; The shear stress is in the first direction; This refers to the shear stress in the second direction. This represents the shear stress in the second direction.

[0091] To balance computational accuracy and efficiency, this embodiment sets the element size to 0.1 μm for the polycrystalline geometric model region and 1 μm for the compact tensile specimen region. After meshing, a total of 23725 CPE4R elements, 56005 CPS4R elements, and 2567 COH2D4 grain boundary cohesive elements are generated. The established crystal finite element model is as follows: Figure 8 As shown.

[0092] Step S7: Perform finite element simulation analysis of hydrogen-induced cracking behavior with different microstructure characteristics to obtain stress-strain data and crack data. In this embodiment, finite element simulation analysis of hydrogen-induced cracking with different microstructure characteristics is performed using grain size as an example, including:

[0093] (1) Support reaction curves and critical stress intensity factor analysis of ferrite-cementite models with different grain sizes at 0% hydrogen concentration

[0094] Tensile simulations were performed on polycrystalline models with different average grain sizes, and the support reaction force-displacement curves were obtained as follows: Figure 9 As shown, the critical stress intensity factor was calculated to quantitatively evaluate the influence of various factors on the fracture toughness of the model. Simulation results show that grain refinement can significantly improve the critical stress intensity factor of the model. When the grain size is 1.0 μm, the critical stress intensity factor is 10.533 MPa·m¹ / ²; while when the grain size is 5.0 μm, the value drops to 9.678 MPa·m¹ / ², a decrease of 8.12%. This phenomenon is attributed to the increased number of grain boundaries brought about by grain refinement. Grain boundaries, as effective barriers to dislocation movement and crack propagation, significantly enhance the strength of the material.

[0095] (2) Crack propagation path analysis of ferrite-cementite models with different grain sizes at 0% hydrogen concentration

[0096] Crack propagation simulations were performed on models with grain sizes of 1 μm and 3 μm, and the evolution process is as follows: Figure 10 As shown, when the grain size is 3 μm, the large grains are continuously distributed, weakening the hindering effect of grain boundaries on crack propagation, resulting in cracks mainly propagating in a straight line. In contrast, when the grain size is 1 μm, the grain boundary density is significantly increased, inducing a significant deflection of the crack path, with the propagation trajectory exhibiting a curved shape at the end. Further observation shows that reducing the grain size significantly promotes the initiation of microcracks: the number of microcracks in the 1 μm model is far greater than that in the 3 μm model. This behavior mechanism stems from the fact that fine grains induce local plastic deformation, causing the crack tip to become blunt, inhibiting its direct penetration into the grain, thereby promoting the formation of microcracks.

[0097] This invention establishes a cross-scale simulation method by coupling molecular dynamics simulation and cohesive force modeling to accurately analyze the hydrogen-induced cracking behavior of metallic materials in hydrogen-exposed environments. Based on multi-scale microstructure characteristics such as grain size and grain boundary angles obtained from metallographic observation and electron backscatter diffraction experiments, a geometric model reflecting the microstructure of the actual material is constructed. The fracture process of micro-interfaces under different hydrogen concentrations is simulated using molecular dynamics methods to obtain traction-separation data and calibrate the core parameters of the cohesive force model. These parameters are then embedded into a polycrystalline finite element model based on Thiessen polygons, achieving parameter transfer and coupled calculation from the microscale to the mesoscale. The cohesive force element accurately describes hydrogen-induced grain boundary damage and crack propagation behavior, quantitatively revealing the influence mechanism of mesoscale factors such as hydrogen concentration, grain boundary characteristics, and grain size on the critical stress intensity factor and crack propagation path. This method, through multi-scale correlation modeling and direct parameter calibration, significantly improves the reliability and prediction accuracy of the model, providing a theoretical basis and engineering-applicable tool for the hydrogen embrittlement resistance design and life assessment of materials for hydrogen-exposed equipment.

[0098] For the foregoing embodiments, in order to simplify the description, they are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, because according to this application, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily essential to this application.

[0099] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Modifications and variations made by those skilled in the art without departing from the spirit and scope of the invention should be within the protection scope of the appended claims.

Claims

1. A molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking, characterized in that, Includes the following steps: Step S1: Conduct metallographic observation experiments on metallic materials to obtain the grain characteristic distribution of metallic materials; Step S2: Conduct electron backscatter diffraction microscopic characterization experiments on metallic materials to obtain the grain boundary angle distribution and grain size distribution of metallic materials; Step S3: Based on the grain feature distribution obtained in step S1 and the grain boundary angle distribution obtained in step S2, construct a molecular dynamics interface model containing initial cracks and hydrogen atoms. Step S4: Perform displacement loading and tensile simulation on the molecular dynamics grain boundary model constructed in step S3 to obtain stress-strain data and traction-separation data of the crack propagation process, and fit the parameters of the cohesive constitutive model. Step S5: Based on the grain size distribution obtained in step S2, a polycrystalline geometric model is generated using the Thiessen polygon algorithm, and a compact tensile specimen model is established on the periphery, which are then combined into a finite element model based on grain boundaries. Step S6: Embed zero-thickness cohesive units at the grain boundaries of the polycrystalline geometric model obtained in step S5, and assign the parameters of the cohesive constitutive model fitted in step S4 to the zero-thickness cohesive units. Step S7: Perform finite element simulation based on grain boundary cohesion model under hydrogen-exposed environment, analyze hydrogen-induced crack propagation behavior of different microstructures, and obtain support reaction force-strain data and crack propagation path data.

2. The molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking as described in claim 1, characterized in that, Step S1 specifically includes: preparing the metal material as a test sample according to the sample preparation requirements of the metallographic microscope, and obtaining the grain characteristic distribution data of the metal material through metallographic observation.

3. The molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking as described in claim 1, characterized in that, Step S2 specifically includes: Based on the surface condition requirements of the electron backscatter diffractometer, the metallic material is prepared as the test sample; The microstructure of metallic materials is characterized by scanning electron microscopy, and the observation data is analyzed and processed using analysis software to obtain crystal characteristic parameters.

4. The molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking as described in claim 1, characterized in that, Step S3 specifically includes: constructing an interface calculation model based on the grain feature distribution and grain boundary angle distribution data according to the structural requirements of the atomic model in molecular dynamics simulation, and obtaining a defect-containing hydrogen-induced crack evolution model by implanting initial cracks and hydrogen atoms.

5. The molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking as described in claim 4, characterized in that, Step S4 specifically includes: applying displacement boundary conditions to the hydrogen-induced crack evolution model according to the technical requirements of the loading process in molecular dynamics simulation, simulating crack propagation behavior through the tensile process, extracting stress-strain data and traction-separation data of the grain boundary region, and obtaining cohesive constitutive model parameters based on bilinear fitting.

6. The molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking as described in claim 5, characterized in that, The stress-strain data and traction-separation data include one or more of the following: stress-strain curves, stress contour maps, and interfacial tension separation displacement curves; the cohesive constitutive model parameters include critical interfacial tension, initial damage displacement, critical damage displacement, stiffness, and critical fracture energy.

7. The molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking as described in claim 1, characterized in that, The generation of the polycrystalline geometric model in step S5 is based on the requirements of the cohesive force model for the geometric modeling of polycrystalline structures.

8. The molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking as described in claim 1, characterized in that, The constitutive model of the cohesive unit in step S6 includes: Elastic phase ( ): ； in, For traction force; For stiffness; This represents the damage displacement; Damage stage ( ): ； ； ； ； in, The damage factor for the cohesive unit; This represents the maximum damage displacement; This represents the maximum equivalent damage displacement under the mixed cracking mode; This is the critical damage displacement; This represents the normal damage displacement; This represents the tangential damage displacement. Free surface ( ): 。 9. The molecular dynamics-cohesive cross-scale simulation method for hydrogen-induced cracking as described in claim 1, characterized in that, The characteristics of different microstructures in step S7 include one or more of the following: grain boundary angle and grain size; the support reaction force-strain data and crack propagation path data include one or more of the following: support reaction force-strain curve, crack initiation location, crack initiation time, crack propagation path and crack propagation rate.

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