Fatigue Evaluation of Flow Drill Screw Joints Using the Equilibrium-Based Structural Stress Method 2020-01-0189
According to increasing the demands of light-weight design in the automotive industry, the usage of thinner and lighter materials such as aluminum alloy has led to significant weight reduction. The joining of these materials has required new technologies in joining/fastening rather than welding. Flow drill screw (FDS) is one of the latest technologies to fasten sheet metal panels.
This paper discusses the results of an evaluation of the fatigue characteristics of FDS joints based on experimental data and observations from the literature. It was observed that the important geometric parameters of FDS joints are the gap between panels and the extruded (or bulged) zone during screwing. Major failure modes were observed as panel failure which cracks grow from the inner surface of the panel around the bulged zone.
In this paper, the fatigue evaluation procedure for FDS joints using the mesh-insensitive equilibrium-based structural stress (ESS) method was proposed. The ESS-based simplified modeling procedure was used for the fatigue evaluation procedure development for FDS joints. The effectiveness and applicability of the ESS-based simplified procedure for modeling and simulating resistance spot welds and self-piercing rivet (SPR) joints has been proven by the previous investigations. After accounting for the geometric and fatigue characteristics of FDS joints, ESS-based simplified procedure and the master S-N curve approach-based this procedure was established. It was observed that the fatigue data in the master S-N curve become consolidated with a small scatter band regardless of panel thickness and panel preparation (with and without clearance hole).
By comparing the master S-N curves for SPR joints and for resistance spot welds in aluminum alloy which were previously constructed, the fatigue behavior characteristics among different groups of joining methods are discussed.
Jeong Hong, Gery Wilkowski
Engineering Mechanics Corp. of Columbus