Quantitative relationship between weld defect characteristic and fatigue crack initiation life for high-cycle fatigue property

摘要

In this paper, the effect of interior defects on high cycle fatigue (HCF) life of welded joint made by narrow-gap arc welding was investigated. The HCF tests were conducted with a stress ratio (R) of - 1 at room temperature, including two specimens pre-tested with R = 0.1. Interior defect fatigue crack origins (IDFCO) like inclusion and pore were studied by fracture surface observation. The crack initiation life (N-i), non-ignorable for short-life specimens, was obtained by excluding the long crack propagation life within the fish-eye area. The traditional threshold value of stress intensity factor at R = 0 (Delta K-th.0) can be regarded as a suitable parameter for fatigue life partition by considering the incremental life in the near-threshold regime. The fatigue initiation life is mainly affected by the applied stress level and projection area of defect. The defect shape plays an important role in the stress distribution at the defect-matrix interface, which is also indirectly affected by defect size due to elastic anisotropy and inhomogeneous microstructure. The combined effect of defect shape and size may induce multi cracks formation at the defect-matrix interface. A new numerical model considering the multi-cracks formation effect was proposed to predict the fatigue initiation life, which agrees with the experimental results.