Fatigue crack growth in welds based on a V-notch model for the short crack propagation at the toe

Abstract

This work presents a new fatigue crack growth prediction model for non-load-carrying fillet welded steel joints. For this joint configuration the fatigue cracks will emanate from the weld toe region. Due to the presence of a V-notch in this region the crack initiation point becomes a point of singularity for the stress field. This may in many cases make it difficult to determine the Stress Intensity Factor Range (SIFR) for small cracks by conventional methods based on Linear Elastic Fracture Mechanics (LEFM). The present approach solves this problem by using the Energy Release Rate (ERR) to determine the SIFR in the small crack growth regime. The model is fitted to crack growth curves from tests with cruciform steel welded joint subjected to constant stress ranges in both axial and bending loading mode. The Paris crack propagation law is adopted and the calculation of SIFR for larger cracks outside the material volume influenced by the V-notch singularity is carried out by the conventional approach. The model gives results in agreement with experimental facts and has also the potential of being extended to variable amplitude loading. The model is also well suited for taking into account the crack initiation phase that is significant for high quality welded joints