Fracture modeling of spot welds and rivets for crash simulation

This paper presents different modeling strategies for spot welds and rivets usable in crash simulations of whole vehicles. The simplified models are based on solid elements and connector elements. The damage parameters are obtained by simulation of specimen tests containing only one spot weld or rivet and conducted under different loading situations (lap-shear, pure tension and peeling) and different loading velocities. Spot welded and riveted component tests have been carried out and simulated for verifying the calibrated spot weld and rivet models. The actual limits are the restrictions of modeling the accurate failure behavior. A spot weld model which is calibrated to fail by peel-out or pull-out fracture has no possibility to change the fracture mode to interfacial fracture. By contrast detailed 3D finite element models with zone specific material properties and advanced micromechanical damage models are able to predict the change of fracture mode from interfaciai to peelout fracture. Of course these detailed models are not applicable to crash simulation of all spot welds of a whole car. But perhaps it is a possibility to model critical spot welds in detail using a multi model coupling for better and more reliable results of spot weld fracture. This paper shows also the necessity of the consideration of the post failure behavior of riveted aluminum joints to represent accurately the load bearing capacity of riveted components. Improvements might be the consideration of a load dependent damage evolution that means a load dependent energy absorption criterion.