三维疲劳裂纹扩展仿真技术研究

应用参数化、模块化有限元建模技术和接触技术仿真半椭圆表面裂纹（前缘曲线和节点），提出了在裂纹前缘形成辐射状奇异单元网格的建模方法和采用有限元接触技术来施加裂纹模型边界条件的方法，实现了裂纹前缘奇异应力场和裂纹模型远场应力的模拟，建立了三维块体初始半椭圆表面裂纹多自由度扩展仿真模型．通过裂纹前缘离散点的正交扩展和拟合得到裂纹扩展前缘形状，使裂纹扩展更加具有自由度．提出了裂纹前缘拟合误差控制扩展步长的方法，使裂纹扩展过程中扩展步长可变．采用参数化、模块化建模技术建立了扩展裂纹模型，实验与仿真结果的比较表明两者基本吻合，说明本文所采用的方法具有很好的实用性．

Study on Simulation Technique of 3D Fatigue Crack Propagation

Using parameterized and modularized finite element model building and contact techniques, the semi-ellipse surface crack （ the front curve and the nodes） was simulated. The model building method of forming radial singular element meshes in the crack front and the method of applying boundary conditions of crack model based on finite element contact technique were put forward. The simulation of the singular stress field of the crack front and the far field stress of the crack model was realized, and then the multiple-freedom propagation simulation model of original semi-ellipse surface crack for the three-dimension block was established. The shape of crack propagation front was obtained by orthogonal extending and fitting of the discrete points in the crack front, which can make the crack propagation have more freedom. Finally, the method of controlling the propagation step length by the fitting error of the crack front was also provided, which made the propagation step length variable during crack propagation process. The extended crack model was rebuilt by building tech-nique of parameterized and modularized model. Its simulation results basically cohere with the test results, which show that the method the paper applied has good practicability.