Verification of numerical modelling of the SPR joint by experimentul stack-up

abstractEN: In recent years self-piercing riveting (SPR) technique became one of the most promising, especially in the automotive industry, for joining different materials, mainly because of lack of several limitations traditionally associated with most widely used spot-welding. Self piercing riveted joints also differ significantly from other types of riveted joints such as those used in aircraft structures owing to the manner in which the joint is produced. In self-piercing riveting, a tubular rivet made usually from a high-strength steel alloy is forced through a pair of partially overlapping sheets that are supported by a circular die with an axisymmetric cavity. Although SPR is already applied by the industry with success, there is still lack of precise design criteria to obtain optimal strength of the joint. This fact limits this technology to be used more often. To have optimum strength of any SPR joint type (various materials, sheet thickness etc.) a set of analysis tools are needed. One is widely verified numerical model and other is experimental tolling allow to quickly join any shape. In Department of Metal Forming Warsaw University of Technology there are some projects carried out related with the SPR process. They are two directions specified: traditional (macro) technology and application of SPR in microforming area. After several trails of numerical modeling of both forming and loading different SPR joints the authors specified a general guidelines to carry out numerical simulaton of the SPR with a success. Now, a design of original experimental tools is verified. Both, forming a joint and its strength became aims of FEM simulation as the most promising tool to analyse various aspects of the joint development. The mechanical response of a self-piercing riveted joint is determined by both the residual stresses after the piercing operation and the stress and displacement fields induced by the applied loads. In this paper three-dimensional finite element analysis of riveted joints is performed to evaluate the load induced local mechanical behavior and response features measured in the laboratory. To consider residual stresses due to piercing two-dimensional analysis of joining process giving information of stress/strain field existing around a joint are performed. First, 2D axisymmetrical FEM model is analysed to obtain SPR joint. Then stress/strain field got from 2D simulation is superimposed on 3D FEM model to analyze strength of a joint by loading in standard test schedule. Finally, experiments on originally designed tool stack up are carried out. The shape of a joint, force flow during joint formation and force flow during loading a jont are compared between FEM simulations and experiments. Numerical simulation of both forming SPR joint and modeling of loading/strength of a joint are performed with commercial software MSC.Marc and MSC.SuperForm based on the FEM. Two sets od dies and thickness of material to be joint were chosen for verification. Finally, comparison of the results of numerical simulations and experimets are presented.score: