Knowledge Bank

Due to increasing emission standards, car manufacturers have begun employing a multi-material auto body construction to reduce vehicle weight. Traditionally, car bodies are spot welded together, however, dissimilar materials cannot be welded, so mechanical fasteners must be used. Current fasteners such as RIVTAC® multi-ridged nails have had success in filling this role, but have had issues with joint strength reliability, due to inherent randomness in the "petal" formation process (the way joining material fractures and rebounds to grip the fastener). This was the first research of its kind and served to investigate and mitigate negative effects of the petal formation process on joint performance. It explored techniques to control the petal formation process and eliminate the need for petaling entirely to improve joint strength reliability. Two pre-treatment mechanisms were developed to address this issue. The first process introduced a set of radial cuts surrounding the fastener insertion site which introduced fracture lines that petals form along. The second process emulated a stamping process where a ram was pressed through the joining material, eliminating the need for petal formation as the ram created an effective predrilled hole. Analytical models were developed to predict plate deflection and stress distribution which were then used to validate finite element models. Finite element models were then ran to predict general joint behavior after each treatment technique. Preliminary FEA results provide a preliminary validation of predicted behavior, but further modeling and physical testing is required to obtain quantitative data about joint performance. This research provided a preliminary exploration of treatment techniques to increase mechanical joint reliability. With further research of treatment techniques, the structural integrity of car bodies is improved resulting in safer vehicles.