Development of a Model for Self-piercing Rivets to Predict Stiffness and Fatigue Life of Automotive Structures

Abstract

Self-piercing rivets are a young technology of spot joining which becomes more and more important in car body engineering because of some advantages compared to other spot joining technologies as for example spot welding. For Finite Element analysis a local model for self-piercing rivets has been developed. The requirements of this model are (1) to represent the correct local stiffness behaviour of self-piercing riveted joints and (2) to be suitable for fatigue analysis. This model was developed analogously to a local model which is already in use for the fatigue assessment of spot welds since several years. The local stiffness behaviour of the model has been adapted to test results of different self-piercing riveted specimens. The local mesh refinement is performed automatically by the SPOT preprocessor module of the fatigue software FEMFAT. Both node dependent and node independent remeshing are supported. The stiffness analysis of a complex structure (similar to car underbody) has shown the usefulness of the model. In the next step a concept for fatigue assessment of self-piercing rivets has been developed. The assessment is basing on linear Finite Element structural stress results. S/N-curves have been summarized in a database and they have been calibrated to test results. A lot of parameter combinations have been considered like rivet diameter, sheet thickness, sheet material and load type (e.g. cross tension load, shear load and combinations). For each load type and for different material classes the database contains specific S/N-curves. Finally fatigue analysis results of the underbody by applying above method are presented and compared with test results. Good correlation has been found. (A) For the covering abstract see ITRD E121867.