Finite element models for spot welds

Abstract

Resistance spot welding is widely used in mass production industries to join components made out of cold formed sheet metal parts. A typical example where such components are used is in the automobile industry. As major contributors to a vehicle’s structural stiffness spot welded joints must be properly modelled for reliable analysis in order to prevent fatigue failure. Proper modelling is also required for the purpose of structural optimisation and to be able to produce sufficient accurate stress and strain fields around the spot weld. This paper considers five different finite element spot weld models loaded in a tensile shear mode. These models are taken from literature. The simplified spot weld models that can be used in conjunction with shell elements within a finite element application software are compared both with their solid model counterpart and with some limited experimental results. The experimental results are used to validate strain fields in the vicinity of the spot welds. The simple finite element models considered in this paper are the single elastic beam model, the rigid beam model, the umbrella model and the nine point contact model. These simple spot weld models are suitable for calculating structural hot spot stresses that can later be used in a fatigue assessment. The main conclusion of this paper is that the stress and strain fields around the spot welds depend on the spot weld model chosen and on the size of adjacent shell elements. This does not discredit the use of these finite element spot weld models for structural optimisation and for structural integrity assessment but sheds some light on which is the best model to use for particular applications.