残余应力对激光修复紧凑拉伸试件疲劳性能的影响

Effect of Residual Stress on Fatigue Performance of Compact Tension Specimen Repaired by Laser

以304不锈钢制作的含裂纹紧凑拉伸试样为研究对象,开展了裂纹尖端激光修复实验研究。基于热力顺序耦合有限元方法,模拟了激光作用后裂纹尖端修复区残余应力的分布情况,并分析了裂纹扩展对应力重分布和塑性区尺寸的影响;同时,得到了考虑残余应力影响的应力强度因子,并由此建立了改进的裂纹扩展速率预测模型以评价修复试件的疲劳性能。最后通过开展疲劳裂纹扩展实验验证了本文模型的有效性。结果表明,裂纹尖端激光修复会使修复区产生残余拉应力,裂纹的扩展会使残余应力场重新分布,并减小裂纹尖端的塑性区尺寸。残余拉应力的存在会增大试件所受载荷的有效应力比,提高疲劳裂纹扩展速率,降低构件的疲劳寿命。

The cracked compact tension specimen made of 304 stainless steel was used as the research object to study the experiment of laser repair at crack tip.Based on the thermal-mechanical sequential coupled finite element method,the residual stress distribution in the vicinity of crack tip was simulated.The influence of crack propagation on the stress redistribution and plastic zone size was analyzed.Meanwhile,the stress intensity factor considering residual stress was obtained.Then,an improved crack growth rate prediction model was established to evaluate the fatigue performance of the repaired specimen.Finally,the effectiveness of the proposed model was verified by the fatigue crack propagation experiment.The results show that laser repair at the crack tip produces residual tensile stress in the repaired area.The crack propagation leads to the redistribution of residual stress field and reduces the plastic zone size at crack tip.The existence of residual tensile stress increases the effective stress ratio of the load,which can increase the fatigue crack growth rate and reduce the fatigue life of the component.