A PROBABILISTIC MODEL FOR INITIATION AND PROPAGATION OF SURFACE CRACKS IN WELDED-JOINTS

Monte Carlo simulations of fatigue in welded joints have been performe d using an approach which combines a model for initiation with a multi ple surface crack propagation model. The results have compared with ex periments on T-plate welded joints in which initiation and propagation of surface cracks were monitored using potential drop techniques. Pre dictions of initiation life using a local strain approach were conserv ative. Despite this underprediction of initiation life, predictions of total fatigue life were very good as a consequence of accurate simula tions of propagation life and the fact that initiation represented on average only 12 to 22% of total life, depending on stress level. The i nitiation model considered variability due to the local weld toe angle and radius, and material strain-life behaviour. The only variability considered in the propagation analysis was the position and timing of initiation events, which leads to variability in coalescence. The unde rprediction of the variability in propagation and total lives was attr ibuted to the underprediction of initiation life and the fact that out -of-plane coalescence effects were ignored.