Fatigue assessment of naval welded assemblies

Abstract

Ship structures are commonly assembled by using welding process and they are submitted to some variable and complex loadings. Moreover, near the weld toe, some local stress concentrations are generated. Accordingly, welded joints could be a critical area regarding fatigue damage. In a previous work, a methodology to predict fatigue life has been developed and tested on butt-welded joints. The present work focuses on more complex assemblies in order to be able to estimate the fatigue life of representative naval structures. The strategy could be split into two steps. First, finite element calculation is performed with constant or variable amplitude loadings in order to analyze the elastic shakedown of the structure. To characterize the material heterogeneity of the welded joint, experimental tests on simulated heat affected zone and some micro-hardness measurements have been conducted. If the structure shakedowns, a post-treatment has been developed to predict the fatigue crack initiation which is based on a two-scale damage model initially developed by Lemaitre et al., using again the heterogeneity of fatigue material properties, in order to obtain an accurate numerical predicted fatigue life. To validate this methodology, some experimental tests have been performed on various welded structures (cruciform joints type representative of naval assemblies) and comparisons between experimental and numerical fatigue life are encouraging.