Method for simulating crack propagation mode of metal material
Through molecular dynamics, the crack propagation process of metal sheet architecture is simulated, and the crack tip stress field and dislocation evolution are analyzed, which solves the problem of difficult to simulate the microkinetic behavior of crack propagation of metal materials in the prior art, and achieves crack propagation In-depth understanding of models and mechanisms and the establishment of multi-scale mechanisms.
Patent Information
- Application Number
- CN202411691708.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-25
- Publication Date
- 2025-02-14
AI Technical Summary
The prior art is difficult to effectively simulate and analyze the microkinetic behavior of crack propagation of metal materials, and it is impossible to obtain crack morphology, crack opening displacement and crack tip dislocation evolution behavior.
Through molecular dynamics, metal sheet architecture is established, single-sided cracks are prefabricated, and different types of loads are applied to simulate the crack propagation process and analyze the crack tip stress field, strain field and dislocation evolution.
In-depth clarification of the crack propagation mode and mechanism of metal materials was achieved, and a multi-scale crack propagation mechanism was established, providing a basis for combating fatigue design and alloy composition design.
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of crack propagation prediction of metal materials, and in particular relates to a method for simulating crack propagation modes of metal materials. Background Art
[0002] During the service process, metal structural parts will gradually develop cracks as the load is continuously applied, and the crack propagation speed directly determines the service life of the structure or even the entire system. Ambient temperature, load size, load type, etc. directly affect the crack propagation rate and mode, which is mainly reflected in the intensity of dislocation movement and precipitation phase behavior inside the metal material. In addition, the precipitation phase, element segregation, crystal orientation, etc. inside the metal material have a significant impact on the crack propagation behavior and mechanism of the material. Exploring the crack propagation mode of metal materials can provide support for understanding the basic properties of the material and establishing a suitable anti-fatigue design method. It can also provide a basis for subsequent alloy composition design and heat treatment system optimization. In order to deeply understand the service performance of metal materials, carry out targeted anti-fatigue design, and extend the service life as much as possible under the premise of ensuring structural safety, it is very necessary to conduct a multi-scale analysis of the crack propagation form of the material. At present, conventional crack propagation tests can only obtain the surface morphology of the crack after fracture. Combined with data-image correlation technology, the crack tip stress field, strain field and other characteristics can be analyzed, but the crack morphology, crack opening displacement and crack tip dislocation evolution behavior cannot be obtained. Summary of the invention
[0003] The technical problem to be solved by the present invention is to provide a method for simulating the crack propagation mode of metal materials in view of the deficiencies in the above-mentioned prior art. Based on molecular dynamics, a metal material plate system structure composed of different metal material elements is established to observe the microscopic dynamic behavior of the crack from load application to fracture. Based on the crack tip morphology and dislocation structure evolution, the crack propagation mode and mechanism are explained, and a multi-scale crack propagation mechanism is established; it has a significant impact on the crack propagation behavior and mechanism of materials such as the precipitation phase, element segregation, and crystal orientation inside the metal material. At the same time, exploring the crack propagation mode of metal materials can provide support for understanding the basic properties of the material and establishing a suitable anti-fatigue design method, and can also provide a basis for subsequent alloy composition design and heat treatment system optimization.
[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for simulating the crack propagation mode of a metal material, characterized in that the method comprises the following steps: Step 1: Use molecular dynamics to establish the metal material plate system structure and prefabricate a single-side crack; Step 2: Apply different types of loads to the metal sheet system structure; Step 3: Relax the structure of the metal sheet and obtain the coordinates and stress values of all atoms; Step 4: Process the deformed metal sheet structure as follows: Step 401, analyzing the morphological characteristics and numerical characteristics of the crack tip stress field and strain field during the deformation process, and analyzing the relationship between the characteristic atoms and the maximum stress, and the relationship between the characteristic atoms and the minimum stress; Step 402, analyzing the crack tip morphology and crack opening displacement at different deformation stages, and calculating the dislocation evolution based on the dislocation extraction algorithm; Step 5: Summarize and analyze the crack propagation mode of metal materials.
[0005] The above-mentioned method for simulating the crack propagation mode of metal materials is characterized in that: in step one, an area is selected on the established metal material plate system structure for division, and the two divided sub-areas are made not to generate interaction force with each other during the process of prefabricating single-sided cracks.
[0006] The above-mentioned method for simulating the crack propagation mode of a metal material is characterized in that: in step 2, by applying different constant motion speeds to the metal material sheet system structure, the type of load applied to the metal material sheet system structure is changed, thereby changing the type of load applied to the atoms in the two sub-regions; When a load acts on the metal material sheet system structure, crack propagation occurs, and temperature control is performed based on the Nose-Hoover hot bath method during the crack propagation process.
[0007] The above-mentioned method for simulating the crack propagation mode of metal materials is characterized in that: in step four, molecular dynamics modeling is used to simulate the morphological characteristics and numerical characteristics of the crack tip stress field and strain field of the two sub-regions during the deformation process, as well as the crack tip morphology and crack opening displacement at different deformation stages.
[0008] The above-mentioned method for simulating the crack propagation mode of metal materials is characterized in that: in step five, at the initial stage of crack propagation, the crack tip morphology is sharp, which is a brittle propagation caused by the rupture of atomic interaction under the action of tensile stress; then the crack is dislocated, and under the dual action of atomic uneven motion and dislocation, the crack rapidly propagates, and the crack tip begins to blunt; when the crack expands to a certain size, the dislocation proliferation and evolution degree intensifies, plastic deformation occurs, resulting in increased crack tip blunting until complete fracture.
[0009] The beneficial effects of the present invention are that by establishing a metal material plate system structure composed of different metal material elements based on molecular dynamics, the microscopic dynamic behavior of the crack in the whole process from load application to fracture can be observed, and based on the crack tip morphology and dislocation structure evolution, the crack propagation mode and mechanism are clarified, and a multi-scale crack propagation mechanism is established; it has a significant impact on the crack propagation behavior and mechanism of materials such as the internal precipitation phase, element segregation, and crystal orientation of the metal material. At the same time, exploring the crack propagation mode of the metal material can provide support for understanding the basic properties of the material and establishing a suitable anti-fatigue design method, and can also provide a basis for subsequent alloy composition design, heat treatment system optimization, etc.
[0010] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Figure 1 This is a diagram of the atomic structure model of the low-density niobium alloy with through-cracks of the present invention.
[0012] Figure 2 This is a schematic diagram of stress distribution during crack propagation at room temperature 300K in the present invention.
[0013] Figure 3 This is a schematic diagram of stress distribution during crack propagation under high temperature 600K conditions of the present invention.
[0014] Figure 4 This is a schematic diagram of stress distribution during crack propagation under high temperature 920K conditions of the present invention.
[0015] Figure 5 This is a diagram of the crack morphology evolution during the crack propagation process at room temperature 300K of the present invention.
[0016] Figure 6 This is a diagram of the crack morphology evolution during crack propagation under high temperature 600K conditions of the present invention.
[0017] Figure 7 This is a diagram of the crack morphology evolution during the crack propagation process under high temperature 920K conditions of the present invention.
[0018] Figure 8 This is the dislocation evolution diagram during crack propagation at room temperature 300K of the present invention.
[0019] Fig. 9 This is the dislocation evolution diagram during crack propagation under high temperature 600K conditions of the present invention.
[0020] Fig.10 The figure is a flowchart of the method of the present invention. DETAILED DESCRIPTION
[0021] like Figures 1 to 10A method for simulating a crack propagation mode of a metal material is shown, the method comprising the following steps: Step 1: Use molecular dynamics to establish the metal material plate system structure and prefabricate a single-side crack; Step 2: Apply different types of loads to the metal sheet system structure; Step 3: Relax the structure of the metal sheet and obtain the coordinates and stress values of all atoms; Step 4: Process the deformed metal sheet structure as follows: Step 401, analyzing the morphological characteristics and numerical characteristics of the crack tip stress field and strain field during the deformation process, and analyzing the relationship between the characteristic atoms and the maximum stress, and the relationship between the characteristic atoms and the minimum stress; Step 402, analyzing the crack tip morphology and crack opening displacement at different deformation stages, and calculating the dislocation evolution based on the dislocation extraction algorithm; Step 5: Summarize and analyze the crack propagation mode of metal materials.
[0022] In the present invention, the metal material plate system structure composed of different metal material elements is established based on molecular dynamics, which can observe the microscopic dynamic behavior of the crack from load application to fracture. Based on the crack tip morphology and dislocation structure evolution, the crack propagation mode and mechanism are explained, and a multi-scale crack propagation mechanism is established; it has a significant impact on the crack propagation behavior and mechanism of materials such as the precipitation phase, element segregation, and crystal orientation inside the metal material. At the same time, exploring the crack propagation mode of metal materials can provide support for understanding the basic properties of materials and establishing appropriate fatigue resistance design methods. It can also provide a basis for subsequent alloy composition design and heat treatment system optimization.
[0023] In the present invention, the test data of low-density niobium alloy is taken as an example. In step 1, based on the element composition of low-density niobium alloy, an atomic structure model with a size of 20a×80a×60a is established, where a is the distance between adjacent atoms, and the overall model contains 389620 atoms. Figure 1 The two regions A and B shown are set to have no interaction during the calculation process to achieve the purpose of prefabricated cracks. The preset crack propagation direction is the positive direction of the Y axis, and the initial crack length is 8a. The crack position is marked in the figure.
[0024] In step 2, when simulating crack propagation behavior, the system first fully relaxes for 50 ps under the NVT ensemble, and then uses the Velocity command to impose a constant motion velocity on the atoms in the upper boundary area of the model. During the crack propagation process, the temperature is controlled based on the Nose-Hoover heat bath method to explore the crack propagation behavior at different temperatures (room temperature 300K, high temperature 600K and high temperature 920K).
[0025] In step 3, the simulation time step is 0.001ps, and the coordinates, stress values and other thermodynamic parameters of all atoms in the two sub-regions are output every 2ps to monitor the temperature and system stability during the simulation in real time. Based on the analysis of dislocation evolution and atomic arrangement configuration, the effect of temperature on crack propagation mechanism is explored.
[0026] In step 401, the stress distribution of the model at the initial moment of unilateral crack extension and during the process under room temperature is as follows: Figure 2 As shown, Figure 2 (a) is a schematic diagram of stress distribution at the beginning of crack extension at room temperature 300K. Figure 2 (b) is a schematic diagram of stress distribution during the crack propagation process at room temperature 300K. By comparing the stress distribution diagrams at different times, it can be seen that the role of the initial load is to open the crack, and when the crack opens to a certain extent, stress concentration will occur in the crack tip area under the action of the tensile load. As the load continues to be applied, the stress in the crack tip area exceeds the yield limit of the material, resulting in plastic deformation, causing the crack to propagate forward, and a butterfly-shaped area is formed in front of the crack tip, namely the crack tip plastic zone, which is consistent with the crack tip observation results of the microscopic crack propagation test. Overall, since the original model contains 4 randomly distributed element atoms, even if the crack is located in the middle of the model, the stress distribution during crack propagation is asymmetric. However, the stress in the area in front of the crack tip along the crack propagation direction is the largest, and generally shows a trend of gradual decrease.
[0027] The calculation results of crack propagation stress distribution under high temperature 600K and 920K environment are as follows Figure 3 and Figure 4 As shown, Figure 3 (a) is a schematic diagram of stress distribution at the beginning of crack extension under high temperature 600K. Figure 3 (b) Schematic diagram of stress distribution during crack extension process at high temperature 600K; Figure 4 (a) is a schematic diagram of stress distribution at the beginning of crack extension under high temperature 920K. Figure 4(b) is a schematic diagram of stress distribution during crack propagation at high temperature of 920K. Similarly, stress is first concentrated at the crack tip, followed by the formation of a butterfly-shaped region. However, in a high temperature environment, atomic motion is more violent, resulting in the area of the region with greater stress in front of the crack tip increasing with increasing temperature. Comparing the stress distribution structure with the arrangement characteristics of different elements in the original model, it can be found that the stress around the Cr atom is always greater. The results of microscopic in-situ crack propagation show that the stress in the area close to the crack tip is equal, but at the microscopic scale, due to the difference in the forces between different atoms, the stress distribution in this area is uneven. In addition, the atomic arrangement in the area with greater stress under room temperature and high temperature environments has changed to a certain extent compared to the initial state, which shows that the change in the atomic arrangement structure causes a change in the forces between atoms. When the external force is greater than the bonding force between atoms, the original structure is destroyed, resulting in dislocations. It should be noted that during the entire extension process, at certain moments, the atoms in front of the crack tip will detach before the atoms at the crack tip, forming holes. As stress continues to be applied, the original crack and the hole merge, resulting in crack extension, such as Figure 3 (b) as shown.
[0028] In step 402, the crack morphology at different times during the crack propagation process at room temperature 300K is as follows: Figure 5 As shown. At t=8.5ps, the tensile stress of the crack tip atoms reaches a peak value, causing the atomic arrangement to change and the crack to begin to expand. In this stage, the crack tip atoms are displaced under the action of external forces. Due to the randomness of the atomic arrangement, there are differences in the displacement of atoms at the same time. The atoms with weaker binding force deviate from their original positions, destroying the original atomic configuration and forming vacancies, which is manifested as the crack expanding forward, while the atoms with stronger binding force have smaller displacements, which is manifested as the crack not expanding forward. In this case, the crack tip morphology is not the flat state at the initial moment. During this stage, the atomic configuration and crack opening size in the crack tip area did not change; when t=15ps, the crack propagation direction was compared with the previous direction, and the crack tip size increased along the Z-axis direction, that is, the crack tip was blunted, and as the load continued to be applied, the crack continued to propagate forward; when t=20ps, the crack morphology was rougher than before, indicating that the stress state in the crack tip area was more complex after the crack tip was blunted, and the crack propagation degrees were different at different positions at the same time; when t=25ps, the rough crack surface proved that the crack rapidly expanded in the same mode during this process, and the crack opening size also increased; subsequently, when the crack size increased to a certain extent, the unbroken part of the system underwent obvious plastic deformation, resulting in a decrease in the crack propagation rate at this time, while the crack opening size continued to increase, and the crack tip was further blunted.
[0029] Figure 6 and Figure 7The evolution of crack morphology during crack propagation in high-temperature 600K and 920K environments, respectively. Comparing the calculation results of crack propagation at room temperature, it can be seen that the crack propagation mode in high-temperature environment is similar to that in room temperature environment, but the higher the temperature at the same time, the rougher the crack surface morphology, which is related to the activity of atomic movement. Due to the violent atomic movement in high-temperature environment, the atomic configuration is easy to change, and the atomic activity is more frequent under the same external force. In addition, the higher the temperature, the more likely it is that micropores and other structures will appear inside the structure, and these micropores will proliferate into hole defects under the action of external forces. The more hole defects are formed in the area in front of the crack tip, the larger the size, and the more frequent evolution will occur in high-temperature environment. These factors promote crack propagation to a certain extent. Similarly, the crack propagation rate in high-temperature environment shows the characteristics of "stable-fast-slowing down", which is similar to the calculation results at room temperature. However, it should be noted that the higher the temperature, the earlier the crack propagation enters the rate slowing stage.
[0030] Based on the analysis of stress field, atomic arrangement and crack morphology during crack propagation under room temperature and high temperature environments, it can be explored that the atomic configuration at the crack tip will change during crack propagation, and the change in atomic configuration will induce the initiation and evolution of dislocation and slip. Figure 8 The figure shows the crack morphology and microstructural features such as dislocations in the crack structure during room temperature crack propagation. As can be seen from the figure, at t=17ps, the crack tip emits the first Shockley partial dislocation along the <0 1 1> direction. Before that, no dislocation structure is formed. This shows that there is no atomic configuration evolution in the early crack propagation process, and the crack propagation is only caused by the uneven separation of atoms in the crack tip area. After that, the length of the Shockley dislocation gradually increases under the action of external force, including more atoms, and begins to form a stacking fault structure. The crack surface begins to become rough under the influence of dislocations, and the crack opening size begins to increase. As the load continues to be applied, the original dislocations continue to proliferate, while the crack tip emits new Shockley dislocations, and induces stacking faults inside the structure. In addition, due to the deepening of the atomic configuration evolution, Stair-rod pressure bar dislocations and Frank partial dislocations appear inside, but Shockley dislocations are still the main ones. With the continuous proliferation and evolution of dislocations, as well as the emission of new dislocations, the crack tip is further blunted; at this time, the dislocations inside the system are still concentrated near the crack tip, and the evolution and proliferation of dislocations provide a higher crack growth rate. When the crack grows to a certain size, the strength of the remaining unbroken part under the action of external force is not enough to maintain the initial atomic configuration, so the dislocations inside the system no longer exist only in the crack tip area. In this case, the dislocations inside the system proliferate in large quantities, and the interactions become more frequent. In the process of repeated dislocation fusion and evolution, the stacking faults are also moving and expanding, and the slip starts to cause plastic deformation of the system. The crack opening size continues to increase while the crack growth rate decreases to complete fracture.
[0031] The dislocation evolution results of the system under high temperature 600K environment are as follows Fig. 9 As shown in the figure. It can be seen from the figure that the time when the crack tip first emits dislocations under 600K conditions is 16.5ps, which is slightly earlier than the time when the crack tip first emits Shockley dislocations under room temperature conditions. This is caused by the more violent movement of atoms in high temperature environments; after 2.75ps, the dislocation at the crack tip proliferates into multiple entangled Shockley dislocations and a single Stair-rod pressure rod dislocation, forming a dislocation wall. Due to the existence of the immovable Stair-rod dislocation, the crack tip here has not been blunted; but when the load continues to be applied, other positions of the crack tip begin to emit dislocations, and new Stair-rod dislocations and other dislocations are formed where the original dislocations are entangled. Combined with the crack morphology at this moment, it can be seen that even if there are a large number of dislocations around the crack tip at this time, due to the existence of Stair-rod dislocations, the movement of the stacking fault here is also hindered to a certain extent, so the crack extends forward a small distance here, and the crack tip has not been blunted. The crack extends forward at the position of the newly emitted dislocation, and the crack opening size increases; the existence of a large number of dislocation structures at the crack tip and more frequent interactions under the action of external forces provide favorable conditions for crack expansion; similar to the room temperature results, after the crack maintains rapid expansion for a certain period of time, the remaining unbroken part of the system undergoes plastic deformation under the action of external forces, after which the crack expansion rate decreases and the crack tip blunting intensifies until it breaks.
[0032] In step five, at the initial stage of crack propagation, the crack tip is sharp, which is a brittle extension caused by the rupture of atoms under tensile stress; then the crack emits dislocations, and the crack rapidly propagates under the dual effects of atomic uneven motion and dislocations, and the crack tip begins to blunt. However, specific dislocation structures and dislocation entanglements will hinder crack propagation to a certain extent; when the crack expands to a certain size, the dislocation multiplication and evolution degree intensify, and because the strength of the unbroken part of the material is not enough to maintain the original atomic configuration under the action of external forces, micropores, dislocations and stacking faults are gradually formed, plastic deformation occurs, and the crack tip blunting is aggravated. Further blunting of the crack tip reduces the crack propagation rate until it completely breaks.
[0033] In this embodiment, in step 1, an area is selected on the established metal material plate system structure for division, and the two divided sub-areas are made to generate no interaction force between each other during the process of prefabricating the single-side crack.
[0034] In this embodiment, in step 2, by applying different constant motion speeds to the metal material sheet system structure, the type of load applied to the metal material sheet system structure is changed, thereby changing the type of load applied to the atoms in the two sub-regions; When a load acts on the metal material sheet system structure, crack propagation occurs, and temperature control is performed based on the Nose-Hoover hot bath method during the crack propagation process.
[0035] In this embodiment, in step 4, molecular dynamics modeling is used to simulate the morphological and numerical characteristics of the crack tip stress field and strain field of the two sub-regions during the deformation process, as well as the crack tip morphology and crack opening displacement at different deformation stages.
[0036] In this embodiment, in step five, at the initial stage of crack propagation, the crack tip is sharp, which is a brittle extension caused by the rupture of atoms under the action of tensile stress; then dislocation occurs in the crack, and the crack rapidly propagates under the dual action of atomic uneven motion and dislocation, and the crack tip begins to blunt; when the crack expands to a certain size, the dislocation multiplication and evolution degree intensifies, and plastic deformation occurs, resulting in increased crack tip blunting until complete fracture.
[0037] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.
Claims
1. A method for simulating crack propagation mode of metal material, characterized in that: The method comprises the following steps: Step 1: Use molecular dynamics to establish the metal material plate system structure and prefabricate a single-side crack; Step 2: Apply different types of loads to the metal sheet system structure; Step 3: Relax the structure of the metal sheet and obtain the coordinates and stress values of all atoms; Step 4: Process the deformed metal sheet structure as follows: Step 401, analyzing the morphological characteristics and numerical characteristics of the crack tip stress field and strain field during the deformation process, and analyzing the relationship between the characteristic atoms and the maximum stress, and the relationship between the characteristic atoms and the minimum stress; Step 402, analyzing the crack tip morphology and crack opening displacement at different deformation stages, and calculating the dislocation evolution based on the dislocation extraction algorithm; Step 5: Summarize and analyze the crack propagation mode of metal materials.
2. A method for simulating crack propagation mode of metal material according to claim 1, characterized in that: In step one, a region is selected on the established metal material plate system structure for division, and the two divided sub-regions are made to generate no interaction force between each other during the process of prefabricating the single-side crack.
3. The method for simulating crack propagation mode of metal material according to claim 2, characterized in that: In step 2, by applying different constant motion speeds to the metal material sheet system structure, the type of load applied to the metal material sheet system structure is changed, thereby changing the type of load applied to the atoms in the two sub-regions; When a load acts on the metal material sheet system structure, crack propagation occurs, and temperature control is performed based on the Nose-Hoover hot bath method during the crack propagation process.
4. The method for simulating crack propagation mode of metal material according to claim 2, characterized in that: In step 4, molecular dynamics modeling is used to simulate the morphological and numerical characteristics of the crack tip stress field and strain field in the two sub-regions during the deformation process, as well as the crack tip morphology and crack opening displacement at different deformation stages.
5. The method for simulating crack propagation mode of metal material according to claim 2, characterized in that: In step five, at the initial stage of crack propagation, the crack tip is sharp, which is a brittle extension caused by the rupture of atomic forces under tensile stress; then dislocation occurs in the crack, and the crack rapidly propagates under the dual effects of atomic uneven motion and dislocation, and the crack tip begins to blunt; when the crack expands to a certain size, the dislocation multiplication and evolution degree intensifies, and plastic deformation occurs, resulting in increased crack tip blunting until complete fracture.