Method for simulating and analyzing fracture toughness of CT (Computed Tomography) sample by introducing residual stress

Abstract

The invention provides a residual stress introduced CT sample fracture toughness simulation analysis method, and belongs to the cross technical field of fracture mechanics numerical simulation and engineering structure safety evaluation. The method comprises the following steps: step 1, establishing a compression numerical model of a CT sample containing a side groove and a pressure head; 2, introducing cracks and establishing a sub-model; 3, calculating a residual stress field under the crack-containing structure; and 4, calculating a model stress field and performing post-processing to obtain fracture parameters. Based on the adopted sub-model technology, the grid requirement of the whole model can be reduced, the calculation precision is improved, the calculation time is saved and the calculation cost is reduced by carrying out grid refinement on the sub-model, and an accurate, quantifiable and controllable initial residual stress field is introduced through out-of-plane local compression LOPC.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary technical field of fracture mechanics numerical simulation and engineering structure safety assessment, specifically involving a method for simulating and analyzing the fracture toughness of CT specimens with residual stress. Background Technology

[0002] In fracture toughness simulation of CT specimens, extremely high-precision meshing is necessary to accurately capture the stress field distribution and crack propagation behavior in the crack tip region. However, extending this high-precision requirement for the local mesh to the entire specimen model leads to a sharp increase in the overall mesh size, significantly consuming computational resources and prolonging computation time.

[0003] Meanwhile, accurately assessing the impact of initial residual stress is crucial for evaluating structural safety. Obtaining an accurate, quantifiable, and controllable initial residual stress field is the primary challenge in numerical simulation. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, the purpose of this invention is to provide a method for simulating and analyzing the fracture toughness of CT specimens by introducing residual stress, which can improve calculation accuracy and reduce calculation costs.

[0005] This invention provides the following technical solution: a method for simulating and analyzing the fracture toughness of a CT specimen with introduced residual stress, comprising the following steps: Step 1: Establish a three-dimensional model of the CT specimen with side grooves and a compression numerical model of the three-dimensional shell discrete rigid indenter; Step 2: Define the crack size, front edge, and crack propagation direction at the center of the CT specimen, set the crack properties, create a sub-model of the CT specimen, and draw the transition mesh between the sub-model and the overall model. Step 3: Under the condition that the indenter is subjected to an external load, the CT specimen is compressed and unloaded to induce plastic strain inside the CT specimen, and the residual stress field at the crack tip is read after unloading. Step 4: Tensile the CT specimen containing the residual stress field, read the stress field of the CT specimen and post-process it to obtain the fracture parameter J.

[0006] Furthermore, the specific process of step 1 is as follows: Step 1.1, Establishment of geometric model: A three-dimensional solid model of the CT sample with side groove is established using finite element analysis software, and a three-dimensional shell model of the indenter is established. Step 1.2, Assigning material parameters: Define the physical property parameters of the CT specimen with side groove in the finite element analysis software, and define the indenter as discrete rigid; Step 1.3, Model Assembly: Assemble the CT sample with side groove and the indenter in the finite element analysis software, and change the position of the indenter by translation. Step 1.4, Assigning Interactions: In the finite element analysis software, define the inertial reference point and mass properties for the three-dimensional discrete rigid indenter; Step 1.5, Mesh Generation: Mesh the model in the finite element analysis software; Step 1.6, Boundary Condition Setting: Apply symmetrical constraints to the two symmetrical planes of the CT specimen with side grooves; set surface contact on the contact surface between the indenter and the CT specimen with side grooves; apply a displacement load to the indenter.

[0007] Furthermore, the specific process of step 2 is as follows: Step 2.1: Based on the interaction settings in Step 1.4, set the crack surface and crack front at the center of the CT sample; Step 2.2, Mesh Generation: For the crack tip, separate the mesh by setting the integration path radius, the number of circumferential and radial meshes in the integration region, and the number of crack leading edge elements. This separates the sub-model region from the entire model. A transition mesh is drawn in the area where the sub-model and the overall model intersect, and a sweep mesh is generated.

[0008] Furthermore, the specific process of step 3 is as follows: Step 3.1: Establish the analysis step; Step 3.2: In the finite element analysis software, submit the solution task to solve the stress field. Residual stress is generated during the solution process through the compression and unloading of the pressure head. Step 3.3: In the visualization module of the finite element analysis software, read the calculation results after the pressure head is completely unloaded in Step 3.2 to obtain the stress field results of the CT sample with side groove after local compression.

[0009] Furthermore, the specific process of step 4 is as follows: Step 4.1: Establish the analysis step; Step 4.2: Based on the residual stress added in Step 3.2, tensile displacement loads are set at the pins, and a solution task is submitted in the finite element analysis software to solve the stress field. Step 4.3: In the visualization module of the finite element analysis software, read the calculation results of the element coordinates and nodal displacements of the crack tip range of the CT model in Step 4.2, process the elements, and complete the calculation of the fracture parameter J.

[0010] By employing the above-described technology, the beneficial effects of the present invention compared to the prior art are as follows: Based on the sub-model technology employed, this invention can reduce the mesh requirements of the overall model, improve computational accuracy, save computation time, and reduce computational costs by refining the mesh of the sub-model. Furthermore, it introduces an accurate, quantifiable, and controllable initial residual stress field through out-of-plane local compression (LOPC). Attached Figure Description

[0011] Figure 1 This is a flowchart of the calculation method according to an embodiment of the present invention; Figure 2 This is a 1 / 4 scale structural diagram of the CT model and indenter model including the side groove, according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the model assembly according to an embodiment of the present invention; Figure 4 This is a schematic diagram showing the crack location and crack propagation direction in an embodiment of the present invention; Figure 5 This is a schematic diagram of the sub-models in the overall model according to an embodiment of the present invention; Figure 6 This is a residual stress field diagram of an embodiment of the present invention; Figure 7 This is a comparison diagram of the residual stress S11 in relation to the magnitude of the compressive displacement of the indenter in this invention; Figure 8 Embodiments of the present invention Calculation diagram; Figure 9 This is a comparison chart of the J-integral values ​​of the compression displacement of the pressure head in this invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0013] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0014] Please see Figures 1 to 9 A method for simulating and analyzing the fracture toughness of CT specimens by introducing residual stress, specifically for 1 / 4 CT specimens with side grooves, includes the following steps: Step 1: Establish a compression numerical model for a 1 / 4 CT specimen with side grooves and an indenter; details are as follows: Step 1.1, Establishment of geometric model: The three-dimensional solid model of the 1 / 4 CT sample with side groove was established using the finite element analysis software Abaqus, and the three-dimensional shell model of the indenter was established. Step 1.2, Assigning material parameters: Define the physical property parameters of the CT specimen through the Abaqus property module, and define the indenter as discrete rigid; Step 1.3, Model Assembly: Use Abaqus' Create Instance module to assemble the 1 / 4 CT specimen with side grooves and the indenter, and change the position of the indenter by translating the instance.

[0015] Step 1.4, Assigning Interactions: Apply an inertial setting to the three-dimensional discrete rigid indenter using Abaqus's interaction module.

[0016] Step 1.5: Mesh Generation: Use the Meshing module in Abaqus software to generate a mesh for the model; Step 1.6, Boundary Condition Setting: Apply symmetrical constraints to the two symmetrical planes of the 1 / 4 CT specimen with side grooves; set surface contact on the contact surface between the indenter and the 1 / 4 CT specimen with side grooves; apply a displacement load to the indenter.

[0017] Step 2: Introduce the crack and create a sub-model; details are as follows: Step 2.1: Based on the interaction settings in Step 1.4, set the crack size, crack front, and crack propagation direction at the center of the CT sample. Then, set the crack singularity after adding the crack.

[0018] Step 2.2, Mesh Generation: For the crack tip, separate mesh generation is performed by setting the integration path radius, the number of circumferential and radial meshes in the integration region, and the number of crack leading edge elements. Transition meshes are drawn for the area where the sub-model and the overall model intersect, and sweep mesh generation is performed.

[0019] Step 3: Calculate the residual stress field in the cracked structure; details are as follows: Step 3.1: Establish the analysis steps, dividing the compression simulation process into 12 analysis steps. The first analysis step is step 0, which performs local compression; the second analysis step is step 1, which completes the compression simulation of 1 / 5 of the compression; the third analysis step is step 2, which completes the compression simulation of 2 / 5 of the compression; the fourth analysis step is step 3, which completes the compression simulation of 3 / 5 of the compression; the fifth analysis step is step 4, which completes the compression simulation of 4 / 5 of the compression; the sixth analysis step is step 5, which completes the compression simulation of 5 / 5 of the compression; and the seventh analysis step is step 6, which completes the entire compression unloading process. Step 3.2: Submit a solution task in the ABAQUS job module to solve the stress field. Residual stress is generated during the solution process through the compression and unloading of the pressure head. Step 3.3: In the visualization module of ABAQUS, read the calculation results of step 3.2 to obtain the stress field results of the 1 / 4 CT sample with side groove during the local compression process.

[0020] Step 4: Calculate the stress field of the model and perform post-processing to obtain fracture parameters; details are as follows: Step 4.1: Establish an analysis step. The entire model calculation process is divided into one analysis step, step1. Apply a displacement load at the pin of the 1 / 4 CT specimen with side groove to complete the model calculation.

[0021] Step 4.2: Based on the residual stress added in step 3.2, tensile displacement load is set at the pin, and a solution task is submitted in the ABAQUS job module to solve the stress field. Step 4.3: In the visualization module of ABAQUS, read the calculation results of the coordinates of the elements and the nodal displacements of the crack tip range of the CT model in Step 4.2, process the elements, and complete the calculation of the fracture parameter J.

[0022] The formula for calculating J is as follows: ; The calculation formula is as follows: ; The calculation formula is as follows: ; The calculation requires extracting the crack opening displacement at the notch edge. Extract the applied force F, plot it, and calculate the area of ​​the shaded surface using integration. .

[0023] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for simulating and analyzing the fracture toughness of a CT specimen by introducing residual stress, characterized in that, Includes the following steps: Step 1: Establish a three-dimensional model of the CT specimen with side grooves and a compression numerical model of the three-dimensional shell discrete rigid indenter; Step 2: Define the crack size, crack front and crack propagation direction at the center of the CT specimen, set crack properties, build the CT specimen sub-model and draw the transition mesh between the sub-model and the overall model; Step 3: Under the condition that the indenter is subjected to an external load, the CT specimen is compressed and unloaded to induce plastic strain inside the CT specimen, and the residual stress field at the crack tip is read after unloading. Step 4: Tensile the CT specimen containing the residual stress field, read the stress field of the CT specimen and post-process it to obtain the fracture parameter J.

2. The method for simulating and analyzing the fracture toughness of a CT specimen with introduced residual stress according to claim 1, characterized in that, The specific process of step 1 is as follows: Step 1.1, Establishment of geometric model: A three-dimensional solid model of the CT sample with side groove is established using finite element analysis software, and a three-dimensional shell model of the indenter is established. Step 1.2, Assigning material parameters: Define the physical property parameters of the CT specimen with side groove in the finite element analysis software, and define the indenter as discrete rigid; Step 1.3, Model Assembly: Assemble the CT sample with side groove and the indenter in the finite element analysis software, and change the position of the indenter by translation. Step 1.4, Assigning Interactions: In the finite element analysis software, define the inertial reference point and mass properties for the three-dimensional discrete rigid indenter; Step 1.5, Mesh Generation: Mesh the model in the finite element analysis software; Step 1.6, Boundary Condition Setting: Apply symmetrical constraints to the two symmetrical planes of the CT specimen with side grooves; set surface contact on the contact surface between the indenter and the CT specimen with side grooves; apply a displacement load to the indenter.

3. The method for simulating and analyzing the fracture toughness of a CT specimen with introduced residual stress according to claim 2, characterized in that, The specific process of step 2 is as follows: Step 2.1: Based on the interaction settings in Step 1.4, set the crack surface and crack front at the center of the CT sample; Step 2.2, Mesh Generation: For the crack tip, separate the mesh by setting the integration path radius, the number of circumferential and radial meshes in the integration region, and the number of crack leading edge elements. This separates the sub-model region from the entire model. A transition mesh is drawn in the area where the sub-model and the overall model intersect, and a sweep mesh is generated.

4. The method for simulating and analyzing the fracture toughness of a CT specimen with introduced residual stress according to claim 1, characterized in that, The specific process of step 3 is as follows: Step 3.1: Establish the analysis step; Step 3.2: In the finite element analysis software, submit the solution task to solve the stress field. Residual stress is generated during the solution process through the compression and unloading of the pressure head. Step 3.3: In the visualization module of the finite element analysis software, read the calculation results after the pressure head is completely unloaded in Step 3.2 to obtain the stress field results of the CT sample with side groove after local compression.

5. The method for simulating and analyzing the fracture toughness of a CT specimen with introduced residual stress according to claim 1, characterized in that, The specific process of step 4 is as follows: Step 4.1: Establish the analysis step; Step 4.2: Based on the residual stress added in Step 3.2, tensile displacement loads are set at the pins, and a solution task is submitted in the finite element analysis software to solve the stress field. Step 4.3: In the visualization module of the finite element analysis software, read the calculation results of the element coordinates and nodal displacements of the crack tip range of the CT model in Step 4.2, process the elements, and complete the calculation of the fracture parameter J.

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