Johan Fremling

Abstract

A method for calculation of the stresses at the end points of laser welds for use in fatigue evaluation is developed. The stresses around the end point are obtained by using a coarse shell model with a mesh size of 5x5 mm.

An analysis has been done on three models, namely a solid model, a fine rounded shell model and a coarse shell model. On those models both a linear elasticity and an elastic-plastic material model of DP600 has been used.

Different weld patterns from earlier fatigue testing and one additional experiment have been studied. The most work have been to develop a finite element method. Those different patterns have been modelled in a finite element program. In the simplified shell model both stiffness and the structural stress have been calculated and compared with fatigue life.

Both for the solid model and the rounded shell model the stress at the end point of the weld is high and in the elastic-plastic region for the material. However, it was found that the stresses approximately 5 mm outside of the weld can be used for fatigue evaluation.

The stress cycles diagram is compared with three different types of stresses from the mesh size of 5x5 mm. This mesh size can describe the stresses around the end point enough accurate. In the 5x5 mm a comparison between the elastic and elastic-plastic material model have been made and the use of an elastic model is good enough.