High Cycle Fatigue strength evaluation of welded joints in handling equipment

Abstract

This study falls within the scope of the fatigue design of handling machines manufactured by the Manitou Group, which are usually composed of a chassis and a boom. These welded assemblies are subjected to fatigue loading conditions and include highly stressed zones acting as crack initiation sites. In view of the geometrical complexity of the structures, the degree of conservatism incorporated in design methods based on the usual international standards is difficult to evaluate. Alternative design approaches based on the structural stress are being developed and used by other companies such as PSA and LOHR. The present work focuses on developing a numerical approach to take into account the local stiffness of welds. The proposed strategy is based on shell finite element modelling of the assembly and an equivalent stiffness matrix for welds. This makes it possible to describe the local mechanical behaviour of seam welds with the computational cost of a shell element based model. To validate the proposed approach, a comparison in terms of stiffness is undertaken for three welded structures using solid finite element models as a reference. The proposed approach is also compared to the Manitou, Fayard and Lohr approaches.