基于交互作用积分的异种金属焊接区域裂纹扩展模拟方法

Numerical Simulation of Crack Propagation in Dissimilar Metal Welded Region Based on Interaction Integral

核电厂中存在大量的异种金属焊接区域,该区域内裂纹扩展的合理评价与核电厂安全运行密切相关。由于焊接区域材料具有显著的非均匀特点,传统的J积分理论在该区域不再具有守恒性,同时大量的运行经验反馈表明,在焊接区域裂纹扩展呈现出明显的偏折现象,传统基于Ⅰ型裂纹扩展的分析方法不再适用。为解决上述问题,本文建立了基于交互作用积分理论的异种金属焊接区域裂纹扩展模拟方法。通过交互作用积分的引入,能够准确计算焊接区域复合型裂纹的应力强度因子,采用最大周向应力等裂纹扩展准则后,能够快速实现裂纹扩展路径的预测。通过将本文方法与实验结果和解析解进行对比分析,验证了当前方法的精度和有效性。该方法的建立对焊接区域裂纹扩展模拟及核电设备安全分析评价具有重要意义。

A large number of dissimilar metal welded materials exist in nuclear power structures,so the accurate evaluation of crack propagation in welded region is highly relevant to the safe service of nuclear power equipment.Due to the significant nonhomogeneity of the materials in the welded region,the traditional J-growth path integral theory is no longer applicable to welded material.Meanwhile,a large amount of feedback from operating experience shows that the crack propagation in the welded region presents an obvious deflection phenomenon.Combined with the extended finite element method,this research established an effective technology to simulate crack propagation in the welded region of dissimilar metals based on the interaction integral theory.By using domain-independent interaction integral,it could accurately calculate the stress intensity factors of an arbitrary crack in the welded region.The prediction of crack propagation path could be realized after using crack propagation criteria such as maximum circumferential stress.By comparing the calculation results of proposed method with the analytical solutions given in the reference,the tiny relative error(<1.5%)indicates the accuracy and effectiveness of the current method.The welded regions in real nuclear power equipment were taken as the research object,and several different regions were selected for compact tensile fatigue tests.The comparison between the experimental results and the simulation results shows that the current method can effectively predict the crack propagation path(the relative error is less than 20%).The study finds that due to the material properties presenting obvious nonhomogeneous characteristics in the welded region,the stress at the crack tip is constantly changing during the crack propagation process.When the crack grows,according to the maximum circumferential stress criterion to determine the direction of its expansion.It can be found that the crack will be deflected at a certain angle,and it is not anⅠ-type crack expansion.This reflects the complexity of fracture behavior for nonhomogeneous material in the welded region,and the crack propagation path strongly depends on the distribution state of material properties near the crack.In summary,the numerical method based on the domain-independent interaction integral given in this paper is of practical engineering significance for the calculation of the stress intensity factors and crack propagation path prediction in welded regions.