残余应力对焊接角接头裂纹扩展性能的影响分析

Influence of Welding Residual Stresses on Crack Growth of Fillet Joints

目的分析焊接残余应力对角接接头裂纹扩展特性的影响。方法基于热弹塑性力学法,建立角接头的有限元模型,计算焊接温度场,并采用热机耦合方法计算焊接残余应力。采用断裂力学方法,分析计算焊趾部位的应力强度因子和裂纹扩展寿命,并对比分析残余应力对裂纹扩展的影响。结果计算得到焊缝的残余应力达到了材料屈服极限,呈拉伸应力状态,其Von Mises应力值为345 MPa。在应力为200 MPa以内,考虑残余应力的前提下,分别使用文献试验得到的数据和IIW标准中的数据作为裂纹扩展参数,应力比R=–1时的裂纹扩展寿命分别为2.61×10^(6)和6.84×10^(5)次循环;在应力比R=0时的裂纹扩展寿命分别为1.16×10^(5)和2.90×10^(4)次循环。结论残余应力会加速裂纹扩展。采用控制变量法,将应力范围设定为常值,当应力比R<0时,残余应力扩大了应力强度因子的范围;在应力比R>0时,残余应力一方面会增大最大应力强度因子,使其接近材料的断裂韧度,同时拉伸残余也提高了平均应力强度因子或者提高了应力比R,在这种情况下,残余应力均会加速裂纹的扩展速度。随着裂纹长度的增加,残余应力对裂纹扩展速率的影响会增大。外载荷和残余应力共同对裂纹扩展产生影响,应力比R和残余应力对裂纹扩展的影响机制相同,在焊接结构寿命评估时,需要综合考虑这2个影响因素。

The work aims to analyze the influence of welding residual stresses on the crack growth of fillet joints.A finite element model of fillet joints was established based on the thermal elastic plastic mechanics,the welding temperature field was calculated,and the welding residual stresses were obtained through thermal mechanical coupling.The fracture mechanics method was used to analyze the stress intensity factor and crack growth rate at the weld toe.The influence of residual stresses on crack growth was compared.The calculated residual stresses of the weld reached the material yield limit and were in a tensile stress state,with Von Mises stress of 345 MPa.Under the stress range of 200 MPa,taking residual stresses into account,data obtained from literature tests and data from IIW standards were used as crack growth parameters,the crack growth life was 2.61×10^(6)and 6.84×10^(5)cycles respectively when stress ratio R=-1;when stress ratio R=0,the crack growth life was 1.16×10^(5)and 2.90×10^(4)cycles respectively.Residual stresses will accelerate crack growth.The control various methods can be used to set the stress range to a constant value.The range of stress intensity factor is enlarged by the residual stresses in the case of the stress ratio R<0.The maximum stress intensity factor is increased after combining the residual stresses under the stress ratio R>0,which is closer to the fracture toughness of the material.Moreover,the average value of stress intensity factor or stress ratio R is changed by the tensile residual stresses.So the crack growth rate is accelerated in this condition.With the increase of crack length,the influence of residual stresses on crack growth rate will increase.Both load and residual stresses have an influence on crack growth,the influence mechanism of stress ratio R and residual stresses on crack growth is the same.Two influencing factors need to be comprehensively considered in the life assessment of welded structures.