Finite-element modelling and updating of laser spot weld joints in a top-hat structure for dynamic analysis

Abstract

Spot welds made by resistance spot welding are used extensively in automotive engineering. However, owing to increasing demands in the use of advanced and lightweight materials, laser welding has become a popular alternative for producing spot welds. Because of the complexity and uncertainties of laser welds and thus formed structures, the finite-element (FE) modelling of the welds for dynamic analysis is a research issue. This article first outlines some of the existing modelling works of spot welds. Then, a hat-plate structure used for this study is described and its FE representations are explained. The welds are modelled using CWELD elements in MSC/NASTRAN and their feasibility for representing laser spot welds is investigated. Numerical results for the initial FE model differ considerably from that of their experimental counterparts; hence, a model updating procedure is carried out to minimize the discrepancy between the two sets of results. In this work, the updating is posed as an optimization problem and is performed using the structural optimization capability (SOL 200) in MSC/NASTRAN. Two stages of updating are conducted, that is (a) updating FE models of individual components and (b) updating an FE model of the welded structure. Crucial steps in updating are explained. It is found that by selecting the right updating parameters, the CWELD element can be used to represent laser spot welds with good accuracy.