Study on the fatigue crack propagation and crack closure of over-matched welding joints

摘要

Overmatched welded joint with a crack in hard weld is simplified as a cracked body of CCP type SHS a hard layer sandwiched between two soft material heterogeneity on fatigue crack growth and crack closure of this model are studied by experimental and elastic-plastic finite element methods. It is found that, residual plastic deformation remaining in the wake of a growing crack tip, which causes crack closure, is affected by the plastic deformation in adjacent soft material near by the crack tip. Both the shape of crack tip plastic zone and stress distribution ahead of crack tip in heterogeneous cracked body ard different from that of homogeneous one. Crack closure (opening) loads are estimated by investigating the changes of crack tip opening displacement during fatigue loading, and a new model of crack tip opening displacement during fatigue loading, and a new model of crack opening process is presented. Because of the difference in the effect of mechanical heterogeneity on displacement of non-fatigue crack and fatigue crack, conventional CTOD can not reflect the real deformation at crack tip of SHS specimens.