Fatigue Life Prediction Method for Laser Screw Welds in Automotive Structures

This paper describes the development of a fatigue life prediction method for Laser Screw Welding (LSW). Fatigue life prediction is used to assess the durability of automotive structures in the early design stages in order to shorten the vehicle development time. The LSW technology is a spot-type joining method similar to resistance spot welding (RSW), and has been developed and applied to body-inwhite structures in recent years. LSW can join metal panels even when a clearance exists between the panels. However, as a result of this favorable clearance-allowance feature of LSW, a concave shape may occur at the nugget part of the joint. These LSW geometric features, the concavity of nuggets and the clearance between panels, are thought to affect the local stiffness behavior of the joint. Therefore, while assessing the fatigue life of LSW, it is essential to estimate the influence of these factors adequately for the representation of the local stiffness behavior of the joint. The method conducted in this study follows the stress-based concept of fatigue analysis techniques which considers the level of stresses in the surrounding sheet metal close to the joint. The developed method is applied to the prediction of the fatigue life of LSW in a car body under rough road conditions. A good correlation is confirmed between the prediction and experiment results.