Approach to transferring force-based fatigue curves into stress-related fatigue curves for clinch joints

Cyclic strength is essential in many lightweight design concepts where the design is to be pushed to the limits of strength. While joining dissimilar metals such as aluminum and steel is a challenge of its own, fatigue life prediction for this joining type is all the more challenging. Here, clinching as a mechanical joining process offers many advantages. However, a generalized evaluation of the fatigue properties is complex since many influencing factors, such as the joint’s geometry, the high plastic deformation, the proportion of bonding mechanisms, have to be considered. Force versus number of cycles (F-N) curves are the established basis to describe the fatigue behavior of clinch joints. However, a generalized evaluation of the service life requires stress versus number of cycles (S-N) curves. This research gives a first approach to transferring F-N curves to S-N curves on the basis of nominal stress determination in the damage relevant clinch cross section. The material combination used, EN AW-6014 and HCT590, offers excellent practical relevance since both materials are widely used in the automotive industry.