EnginSoft - CAE Conference Abstracts

EnginSoft International Conference 2011
CAE Technologies for Industry

Finite Element Models for Assessing the Structural Integrity of Spot Welds

Muscat Martin - University of Malta
Mollicone Pierluigi - University of Malta

Abstract

Resistance spot welding is widely used in mass production industries to join sheet metal parts together. Normally such components need to resist both static and cyclic loading. Good design methodologies and mathematical models need to be used in order to ensure spot welded components that remain fit for their purpose during their design life time. This paper is on the area of fatigue assessment of spot welds namely on the structural hot spot stress approach for analysing the structural integrity of spot welds. Five different finite element spot weld models under a tensile shear loading mode were analysed using the finite element software package ANSYS. The paper presents a comparison exercise between the results obtained from the spot weld models. A comparison with some experimental specimens was made in order to validate stress and strain results in the vicinity of the spot welds. The spot weld models analysed were the single elastic beam model, the rigid beam model, the umbrella model, the multi point contact model and the solid element model. The solid element model served as a means to verify results obtained from shell and beam models.
Results indicate that some distance away from the spot weld, all shell and beam finite element models and experimental models predict the same strain values. At a distance of approximately one diameter away from the spot weld edge, strain values start to diverge with the umbrella model predicting the highest strain value at the edge of the spot weld. A comparison of structural stress obtained from the different finite element models give similar trends. The solid element model shows that the highest stress did not occur at the spot weld edge but some distance away within the heat effected zone. Converged results from the solid model do not match the experimental results as accurately as the beam and shell models indicating that thin she et components are best modelled using the latter kind of elements. A mesh convergence study for the shell and beam models was carried out with the conclusion that the umbrella model is the least mesh sensitive spot weld model available to calculate structural stress values. This indicates that the umbrella model lends itself quite useful for large spot welded sheet metal components such as automobile bodies. Structural stress obtained using the umbrella model can then be used in a fatigue assessment of spot welded structures.