Estimating the fatigue behaviour of welded joints

The present work is concerned with an attempt to predict the fatigue strength of welded joints by means of a fracture mechanics approach that takes into account the fatigue behaviour of short cracks. The methodology estimates the fatigue crack propagation rate as a function of the difference between the applied driving force and the material threshold for crack propagation, a function of crack length. The fatigue strength of butt-welded specimens stressed transversely was analyzed. Experimental results from the literature were used for comparisons. Good estimations are obtained by using only the fatigue limit and the fatigue propagation threshold for long cracks corresponding to the base metal, and the applied stress distribution along the crack path obtained from simple FE models. The influence of plate thickness, initial crack length and reinforcement angle on fatigue strength of butt-welded joints was analyzed and results show good agreement with experimental trends. In order to verify the ability of the methodology to estimate the fatigue behaviour of welded joints, a dedicated experimental methodology have to be implemented for the detection and monitoring of the development of surface small cracks initiated at weld toes. Some initial results of a multi-strain gauges technique implemented for those purposes are also shown