Material fracture numerical analysis method based on cohesion model in hydrogen environment

Abstract

The invention discloses a material fracture numerical analysis method based on a cohesion model in a hydrogen environment. The method comprises the following steps: carrying out an unnotched sample tensile experiment in air; carrying out a hydrogen permeation experiment; carrying out an air environment fracture experiment; a series of high-pressure hydrogen charging and hydrogen measuring experiments are carried out; simulating stress distribution and hydrogen distribution of the notch sample; according to a simulation result, selecting a corresponding hydrogen environment, and carrying out a fracture experiment in the environment; and hydrogen damage simulation based on the cohesion model is carried out according to parameters obtained by the experiment. According to the method, the tension displacement relationship of a cohesion region is taken as a core, and the metal tensile fracture simulation process is researched by depending on finite element sequential coupling simulation and combining related performance in a hydrogen environment. According to the method, the required experimental quantity is small, and a load-displacement curve in the tensile process in the hydrogen environment can be well reproduced.

Description

Technical Field

[0001] This invention belongs to the field of materials fracture mechanics and numerical simulation technology, and specifically relates to a numerical analysis method for materials fracture behavior combined with a cohesive force model in a hydrogen environment. Background Technology

[0002] Hydrogen energy is the cleanest potential energy source and can effectively mitigate the greenhouse effect. Vigorously developing hydrogen energy has become an urgent need for my country's energy transition. However, during hydrogen storage and transportation, the metal materials in contact with it may suffer hydrogen damage and subsequently fail. Hydrogen damage refers to the process by which hydrogen gas decomposes into hydrogen atoms through adsorption and dissociation, entering the interior of metal materials. This leads to a decrease in the material's toughness or plasticity, causing ductile damage or even cracking in hydrogen-exposed materials. Therefore, evaluating traditional and newly developed materials in hydrogen environments is essential.

[0003] However, for specific materials, a systematic evaluation of their material properties in a hydrogen environment is required. This necessitates extensive experiments at different hydrogen pressures, which presents drawbacks such as high experimental risks and long experimental cycles, resulting in a relative scarcity of research on the damage of hydrogen-exposed materials in a hydrogen environment. Numerical simulation methods, such as finite element analysis, have become important tools for studying hydrogen embrittlement processes, providing deeper guidance for exploring and developing novel hydrogen-resistant materials and designing hydrogen storage and transportation engineering. Currently, numerical analysis methods for material fracture in hydrogen environments can be broadly classified into two categories. The first uses micromechanical models to study ductile fracture, including void nucleation and growth aggregation, such as the Gurson-Tvergaard-Needleman (GTN) model. The second category uses phenomenological models of ductile fracture, such as the cohesive zone model. In practical applications, these methods generally require obtaining relevant model parameters, such as cohesive energy, initial stiffness, damage initiation stress, and damage initiation displacement. Existing research generally calculates the impact of hydrogen on the mechanical properties of materials using empirical formulas, which have limited applicability to specific steels, resulting in low accuracy of the calculation results.

[0004] This method combines hydrogen embrittlement evaluation experiments, hydrogen diffusion simulations, and fracture simulations in hydrogen environments, resulting in highly accurate, realistic, and practically applicable data. It provides theoretical guidance for studying the hydrogen embrittlement behavior of materials under complex environments. Furthermore, this method obtains the local hydrogen content at specific locations under service conditions through simulation calculations, and then conducts mechanical evaluation experiments in hydrogen environments accordingly, effectively reducing the amount of experimentation and demonstrating high efficiency and economy.

[0005] Patent application No. 202410261154.X discloses a numerical analysis method for the brittle fracture of a small punch specimen in a hydrogen environment. This method uses Abaqus finite element software and simulates the fracture of the small punch specimen in a hydrogen environment using a GTN model through subroutines, which differs significantly from the method presented here.

[0006] Patent application No. 202310737859.X discloses a method for predicting the cyclic cohesion model of hydrogen-induced fatigue crack propagation in subsea pipeline steel. This method uses a finite element model, applying cyclic stress to the model to predict the hydrogen-induced fatigue crack propagation process. This method is based on secondary development of the finite element model, implementing fatigue damage at the crack tip through subroutines, and the impact of the hydrogen environment on material properties is derived from theoretical formulas. In contrast, this proposed method does not require secondary development of the finite element model, and the hydrogen-related properties of the material are obtained experimentally, showing a significant difference from this proposed method.

[0007] Patent application No. 202311810463.X discloses a method for simulating hydrogen compatibility under high pressure based on hydrogen diffusion. This method uses the results of smooth slow tensile simulation tests and fracture toughness tests to assess high-pressure hydrogen embrittlement, and can obtain the hydrogen embrittlement properties of materials under different hydrogen pressure environments. However, this method does not utilize numerical simulation methods, involves a large amount of experimentation, and differs significantly from the method presented here.

[0008] Patent application No. 202311299347.6 discloses a numerical analysis method for hydrogen embrittlement of pipes under multi-field coupling conditions. This method focuses on the tension-displacement relationship within the cohesive zone, conducting multi-field sequential coupling to simulate the tensile fracture process of metals at any hydrogen diffusion moment; and performs multi-field direct coupling numerical calculations and analyses of hydrogen-induced fracture based on assumptions about hydrogen diffusion behavior. This method employs electrochemical hydrogen production and charging, and optimizes the theoretical relationship between hydrogen adhesion rate and metal cohesion based on experimental results. This method, however, obtains hydrogen concentrations in the material under different hydrogen pressures through high-pressure gaseous hydrogen charging, and conducts fracture toughness experiments under specific hydrogen pressures based on simulation results, showing significant differences from this method.

[0009] The paper titled "Numerical Simulation of Hydrogen-Induced Hysteresis Fracture of AISI4135 High-Strength Steel Based on Cohesive Model" uses the finite element method ABAQUS software and a cohesive model to predict the hysteresis fracture time and crack initiation location of pre-charged H-filled cylindrical notched AISI4135 high-strength steel specimens under constant tensile load. However, this paper uses the calculated H concentration-cohesive energy relationship as the initial simulation condition and does not conduct hydrogen embrittlement evaluation tests under hydrogen conditions for the simulated steel, which differs significantly from the method presented here. Summary of the Invention

[0010] The purpose of this invention is to provide a numerical analysis method for material fracture based on a cohesive model in a hydrogen environment. This method focuses on the tension-displacement relationship within the cohesive region, relying on sequential coupled finite element simulation and combining relevant properties under hydrogen conditions to study the tensile fracture simulation process of metals. This invention requires fewer experiments and can effectively reproduce the load-displacement curves of the tensile process in a hydrogen environment.

[0011] To achieve the above objectives, the present invention employs the following technical solution:

[0012] A numerical analysis method for material fracture based on a cohesive model in a hydrogen environment includes the following steps: conducting tensile tests on unnotched samples in air; conducting hydrogen permeation tests; conducting fracture tests in an air environment; conducting a series of high-pressure hydrogen charging and hydrogen measurement tests; simulating the stress distribution and hydrogen distribution of notched samples; selecting a corresponding hydrogen environment based on the simulation results and conducting fracture tests under that environment; and conducting hydrogen damage simulation based on the cohesive model based on the experimental parameters.

[0013] The specific method is as follows:

[0014] 1) Conduct tensile tests on unnotched samples in air to obtain the mechanical properties of the experimental steel, including the engineering stress-engineering strain curve, Young's modulus, and Poisson's ratio; and convert the engineering stress and engineering strain into true stress and plastic strain according to the following formulas to obtain the true stress-plastic strain curve.

[0015]

[0016]

[0017]

[0018] In the formula, True stress, For engineering stress, For engineering contingency, For true response, For plastic strain, Young's modulus;

[0019] 2) Hydrogen permeation experiments were conducted on the experimental steel using a DS dual electrolytic cell via electrochemical hydrogen charging to obtain the hydrogen diffusion rate of the experimental steel;

[0020] 3) Process CT specimens and conduct air environment fracture tests to obtain the fracture toughness of the experimental steel under hydrogen-free conditions. And calculate the cohesive energy-related parameters using the following formulas;

[0021]

[0022]

[0023]

[0024] In the formula, For cohesive energy, For fracture toughness in a hydrogen environment, For Young's modulus, Poisson's ratio, For damage initiation stress, This is the fracture displacement. For initial stiffness, This represents the initial displacement of the damage.

[0025] 4) Conduct a series of high-pressure hydrogen charging experiments. After hydrogen charging, use a hydrogen analyzer to measure the hydrogen content in the steel. Establish the relationship between hydrogen pressure and hydrogen content in the steel per unit time for the experimental steel type, and clarify the initial hydrogen content in the steel under different hydrogen environments.

[0026] 5) Sequential coupling simulation was performed using Abaqus finite element software, based on the service environment. Selecting the initial hydrogen content By simulating stress concentration and hydrogen concentration in notched tensile samples during service, the local hydrogen content at stress concentration points of the material under stress was obtained. ;

[0027] 6) Based on the simulated local hydrogen content in the steel Select the corresponding hydrogen pressure Fracture experiments were conducted under the same hydrogen environment to obtain the fracture toughness of the experimental steel under the corresponding hydrogen environment. And calculate the relevant parameters of cohesion;

[0028] 7) Based on the calculated parameters, material damage simulation based on the cohesive force model and the hydrogen-related tension-displacement model is carried out using finite element software to obtain the material fracture behavior in hydrogen-free environment and specific hydrogen environment.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. By combining hydrogen permeation experiments, high-pressure hydrogen charging and hydrogen measurement data, and finite element sequential coupling simulation, a realistic hydrogen pressure-hydrogen content mapping relationship was established, which significantly improved the accuracy of hydrogen embrittlement fracture behavior prediction.

[0031] 2. By using simulation to obtain local hydrogen concentration under service environment, targeted hydrogen pressure verification experiments can be carried out, which greatly reduces the amount of experiments compared with traditional full-range hydrogen pressure testing and effectively improves R&D efficiency.

[0032] 3. Effectively avoids the risks of high-pressure hydrogen charging experiments and reduces safety costs.

[0033] 4. No secondary development of finite element software such as Abaqus is required. Standardized hydrogen damage simulation can be achieved based on measured parameters, making it highly versatile. Attached Figure Description

[0034] Figure 1 This is a flowchart of the present invention.

[0035] Figure 2This is a stress distribution diagram according to an embodiment of the present invention.

[0036] Figure 3 This is a hydrogen distribution diagram from an embodiment of the present invention.

[0037] Figure 4 These are simulation results of the fracture behavior of experimental steel under air and hydrogen environments in embodiments of the present invention. Detailed Implementation

[0038] The specific embodiments of the present invention will be further described below with reference to the examples. The following examples are used to specifically illustrate the content of the present invention. These examples are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0039] A numerical analysis method for material fracture based on a cohesive model in a hydrogen environment includes the following steps: conducting tensile tests on unnotched samples in air; conducting hydrogen permeation tests; conducting fracture tests in an air environment; conducting a series of high-pressure hydrogen charging and hydrogen measurement tests; simulating the stress distribution and hydrogen distribution of notched samples; selecting a corresponding hydrogen environment based on the simulation results and conducting fracture tests under that environment; and conducting hydrogen damage simulation based on the cohesive model based on the experimental parameters.

[0040] The specific method is as follows:

[0041] 1) Conduct tensile tests on unnotched samples in air to obtain the mechanical properties of the experimental steel, including engineering stress-engineering strain curves, Young's modulus, and Poisson's ratio; and convert engineering stress and engineering strain into true stress and plastic strain according to the following formulas to obtain true stress-plastic strain curves.

[0042]

[0043]

[0044]

[0045] In the formula, True stress, For engineering stress, For engineering contingency, For true response, For plastic strain, Young's modulus;

[0046] 2) Hydrogen permeation experiments were conducted on the experimental steel using a DS dual electrolytic cell via electrochemical hydrogen charging to obtain the hydrogen diffusion rate of the experimental steel;

[0047] 3) Process CT specimens and conduct air environment fracture tests to obtain the fracture toughness of the experimental steel under hydrogen-free conditions. And calculate the cohesive energy-related parameters using the following formulas;

[0048]

[0049]

[0050]

[0051] In the formula, For cohesive energy, For fracture toughness in a hydrogen environment, For Young's modulus, Poisson's ratio, For damage initiation stress, This is the fracture displacement. For initial stiffness, This represents the initial displacement of the damage.

[0052] 4) Conduct a series of high-pressure hydrogen charging experiments. After hydrogen charging, use a hydrogen analyzer to measure the hydrogen content in the steel. Establish the relationship between hydrogen pressure and hydrogen content in the steel per unit time for the experimental steel type, and clarify the initial hydrogen content in the steel under different hydrogen environments.

[0053] 5) Sequential coupling simulation was performed using Abaqus finite element software, based on the service environment. Selecting the initial hydrogen content By simulating stress concentration and hydrogen concentration in notched tensile samples during service, the local hydrogen content at stress concentration points of the material under stress was obtained. ;

[0054] 6) Based on the simulated local hydrogen content in the steel Select the corresponding hydrogen pressure Fracture experiments were conducted under the same hydrogen environment to obtain the fracture toughness of the corresponding experimental steel. And calculate the relevant parameters of cohesion;

[0055] 7) Based on the calculated parameters, material damage simulation based on the cohesive force model and the hydrogen-related tension-displacement model is carried out using finite element software to obtain the material fracture behavior in hydrogen-free environment and specific hydrogen environment.

[0056] Example:

[0057] 1. Select experimental steel and finely process it into smooth round bar specimens. Conduct tensile tests in air to obtain the basic mechanical properties of the experimental steel, including engineering stress-engineering strain curves, Young's modulus, Poisson's ratio, etc.; and convert the engineering stress and engineering strain into true stress and plastic strain to obtain true stress-plastic strain curves.

[0058] 2. Experiments on hydrogen permeation: Hydrogen permeation experiments were conducted on experimental steel using a DS double electrolytic cell through electrochemical hydrogen charging to obtain the hydrogen diffusion rate in the experimental steel.

[0059] 3. Process CT specimens, conduct air environment fracture tests to obtain the fracture toughness of the experimental steel under hydrogen-free conditions, and calculate the relevant parameters of cohesive energy.

[0060] 4. Using the experimental steel from step 1, process multiple sets of hydrogen-measuring samples and conduct a series of high-pressure hydrogen charging experiments. After hydrogen charging is completed, measure the hydrogen content in the steel using a hydrogen analyzer. Determine the initial hydrogen content in the steel under different hydrogen environments.

[0061] 5. Using Abaqus finite element software, a stress and hydrogen diffusion model of the notched tensile specimen was established. Through sequential coupling simulation, the stress concentration and hydrogen concentration of the notched tensile specimen during service were simulated to obtain the local hydrogen content at the stress concentration points of the material under stress. Figure 2 and Figure 3 As shown. The relevant parameters for the embodiment are: -10MPa 2ppm 4.5ppm -50MPa.

[0062] 6. Based on the simulated local hydrogen content in the steel, select the corresponding hydrogen pressure and conduct fracture experiments under this environment to obtain the fracture toughness of the experimental steel under hydrogen conditions. And calculate the relevant parameters of cohesion.

[0063] 7. Based on the calculated parameters, material damage simulations were conducted using finite element method software, based on the cohesive force model and the hydrogen-related tension-displacement model, to obtain the material fracture behavior in hydrogen-free environments and specific hydrogen environments. The results are as follows: Figure 4 As shown in Table 1, the specific mechanical properties and simulated usage parameters of the experimental steel are as follows.

[0064] Table 1 Mechanical properties of the steel plates in the embodiments of the present invention and the parameters required for simulation

[0065]

Claims

1. A numerical analysis method for material fracture based on a cohesive force model in a hydrogen environment, characterized in that, Specifically, the methods and steps are as follows: 1) Conduct tensile tests on unnotched samples in air to obtain the mechanical properties of the experimental steel, including the engineering stress-engineering strain curve, Young's modulus, and Poisson's ratio; and convert the engineering stress and engineering strain into true stress and plastic strain according to the following formulas to obtain the true stress-plastic strain curve. In the formula, True stress, For engineering stress, For engineering contingency, For true response, For plastic strain, Young's modulus; 2) Hydrogen permeation experiments were conducted on the experimental steel using a DS dual electrolytic cell via electrochemical hydrogen charging to obtain the hydrogen diffusion rate of the experimental steel; 3) Process CT specimens and conduct air environment fracture tests to obtain the fracture toughness of the experimental steel under hydrogen-free conditions. And calculate the cohesive energy-related parameters using the following formulas; In the formula, For cohesive energy, For fracture toughness in a hydrogen environment, For Young's modulus, Poisson's ratio, For damage initiation stress, This is the fracture displacement. For initial stiffness, This represents the initial displacement of the damage. 4) Conduct a series of high-pressure hydrogen charging experiments. After hydrogen charging, use a hydrogen analyzer to measure the hydrogen content in the steel. Establish the relationship between hydrogen pressure and hydrogen content in the steel per unit time for the experimental steel type, and clarify the initial hydrogen content in the steel under different hydrogen environments. 5) Sequential coupling simulation was performed using Abaqus finite element software, based on the service environment. Selecting the initial hydrogen content By simulating stress concentration and hydrogen concentration in notched tensile samples during service, the local hydrogen content at stress concentration points of the material under stress was obtained. ; 6) Based on the simulated local hydrogen content in the steel Select the corresponding hydrogen pressure Fracture experiments were conducted under the same hydrogen environment to obtain the fracture toughness of the experimental steel under the corresponding hydrogen environment. And calculate the relevant parameters of cohesion; 7) Based on the calculated parameters, material damage simulation based on the cohesive force model and the hydrogen-related tension-displacement model is carried out using finite element software to obtain the material fracture behavior in hydrogen-free environment and specific hydrogen environment.

Images