裂纹尖端各向异性塑性的研究

Study of Anisotropy Plastisity of Crack Tips

对于有裂纹扩展的平面应力问题,阐述了延性铝合金裂尖实测位移场和HRR位移场的差异不能用裂尖弹塑性渐近解的高阶项来拟合。基于垂直和平行于裂纹线的实测对数位移场的斜率不同,在裂纹尖端附近假设存在由大塑性变形导致的各向异性应变硬化。建立了裂纹尖端各向异性塑性模型,发展了莫尔干涉光测实验/数值分析的杂交方法。分析了裂纹前方、沿着θ=0°径向线上的屈服面各向异性的畸变规律。对于相同的实测应变场,用各向异性模型得到的应变能密度和有效应力比用各向同性塑性公式的计算值约大20%。对于延性稳态裂纹扩展,可指望在裂尖附近由各向异性塑性计算的近场J积分值与实验测定的或远场各向同性计算的J积分值趋于吻合。

As far as a plane—strain problem with crack propagation is concerned,the previous experimental investigations of the elasto — plastic crack tip field on ductile aluminum alloys using moire interferometry showed the possible existence of anisotropic strain hardening behavior in this field,which is often described as of isotropic plasticity.In this paper,a crack tip anisotropic model is proposed and a combined moire interferometric/numerical analysis is conducted to evaluate the crack tip anisotropic behavior.Experiments have identified the crack tip anisotropic plasticity and the reasonableness of its anisotropic parameters.Results also indicate that the effective stresses and the strain energy density calculated from this model are about 20% larger than those from the isotropic assumption,therefore,it may be suggested that a path —independent anisotropic J-contour integral exists in the presence of ductile stable crack propagation.