焊接残余应力对7N01铝合金疲劳裂纹扩展影响

Influence of welding residual stress in fatigue crack growth of 7N01 aluminum alloy

关键词:  焊接残余应力  裂纹扩展  7N01铝合金  尺度效应

Key words:  welding residual stress  fatigue crack propagation behavior  7N01 aluminum alloy  length scale

摘要:

焊接残余应力作为平均应力影响裂纹扩展. 将残余应力与外载平均应力分离，通过构建典型焊接残余应力场，借助扩展有限元计算焊接残余应力场的应力强度因子. 开展了紧凑拉伸（CT）试样的疲劳扩展试验，基于Walker公式将裂纹尖端平均应力强度因子K_m（静态量）和应力强度因子幅值ΔK（动态量）分离，获得疲劳裂纹扩展速率da/dN与K_m及ΔK的非线性关系. 结果表明，不同外载荷下，应力比与裂纹长度为非线性关系；残余应力对裂纹扩展存在尺度效应：CT试样裂纹长度小于2 mm时，残余应力场明显影响疲劳裂纹扩展速率；当裂纹长度大于2 mm，外载荷为主导因素.

Abstract:

Welding residual stress affects crack propagation as an average stress. Residual stress was separated from the average load stress. By constructing a typical welding residual stress field, the stress intensity factor of the welding residual stress field was calculated with the extended finite element method. The fatigue expansion test of the compact tensile (CT) specimen was carried out. Based on the Walker formula, the average stress intensity factor K_m (static amount) at the crack tip and the magnitudeΔK (dynamic amount) of the stress intensity factor were separated to obtain the nonlinear relationship between da/dN versus K_m andΔK. The results showed that the stress ratio was nonlinear with the crack length under different external loads and the residual stress had a scale effect on crack propagation. When the crack length of CT specimen was less than 2 mm, the residual stress field obviously affected the fatigue crack growth rate while the external load was the dominant factor, when the crack length of CT specimen was more than 2 mm.