Predicting the fatigue strength of small thickness welded joints using the implicit gradient method

Abstract

This paper discusses the problem of the fatigue behaviour of small thickness welded joints using the implicit gradient method. Welds have been designed using 3D CAD and then subjected to finite element analysis, using the same computational procedure developed in the past for large thickness welded joints. In order to determine the Woehler curves for the various test series described in the literature, reference shall be made to either a monoaxial strength criterion or a multiaxial strength criterion capable of more efficiently evaluating the effect of a complex stress state while maintaining linear elastic behaviour for the material. The fatigue fault initiation zone is automatically evaluated by the computational procedure which indirectly returns the Woehler curve for the particular test. Application of the computational procedure to several test series taken from the literature has been performed for 2 mm thick sheets, predicting that the implicit gradient method may be applied to assess welded joints independently of the dimensions of the main plate and the shape of the weld bead.