An assessment of simple material behaviour models for predicting the mechanical ratchetting of a stepped beam

Abstract

Finite element programs are often used, without experimental verification, to predict the elastic-plastic behaviour of components, but most programs only contain simple material behaviour models. In this paper, the results from three lead alloy stepped beam components, subjected to steady axial load and cyclic bending, are compared with predictions based on elastic-perfectly plastic, isotropic hardening, and kinematic hardening material behaviour models. These comparsions show that under severe load conditions, in which cyclic plasticity occurs, none of these simple models provides good predictions for the ratchetting behaviour of the beams. This is because the models do not accurately describe the cyclic elastic-plastic behaviour of the lead alloy which is similar to that of many engineering materials. It is concluded that the simple elastic-plastic material behaviour models included in most finite element packages will have to be extended to include more accurate models of material cyclic behaviour if they are to provide accurate predictions for component behaviour.