Spot-welded joints subjected to shear-tension loading. Part 1: Notch stress and strain range predictions and estimates for repeated loading

Abstract

A three-dimensional finite element model has been used to study the cyclic elastic-plastic stress and strain characteristics of a spot-welded joint subjected to repeated shear-tension loading. Four geometries, having low, medium, and high notch elastic stress concentration factors, are considered in this investigation. Two simple material behaviour models, e.g. elastic-perfectly plastic and kinematic hardening, are assumed. All results have been normalized with respect to material properties so that they can be applied to all geometrically similar spot-welded joints from other materials, which may be represented by the same material models. Normalized maximum steady state strain ranges are plotted as a function of the nominal load for the range of material hardening assumptions and notch elastic stress concentration factors. These plots can be used in the low cycle fatigue life design of such geometrically similar spot-welded specimens. The paper also compares finite element steady state strain range predictions with values estimated using simple notch stress-strain conversion rules for the four geometries and a range of nominal stresses. From this study, a ‘notch plastic flow sensitivity factor’, qp, to be used in conjunction with an intermediate rule, is suggested for estimating the strain range. Finally, a strain range estimate methodology, based on the notch elastic stress concentration factor, coupled with a multiaxial fatigue criterion and an intermediate rule, is then developed for this type of specimen and loading.