Spot Weld Fatigue Correlation Improvement in Automotive Structures Using Stress Based Approach with Contact Modelling

In automotive Body-In-White (BIW) structures, stiffness and the fatigue behavior is greatly influenced by the properties of its joints. Spot welding is one of the most widely used process for joining of sheet metals in BIW. Spot weld fatigue life under Accelerated Durability Test (ADT) is crucial for durability performance of BIW structures. Experience of BIW validations highlighted more number of spot weld failures in CAE when compared to actual tests. Hence, lot of iterations in the form of design modifications are required to be carried out to make these spot welds meet the targets which increases design & development time as well as cost. Current practice uses force-based approach for predicting spot weld fatigue life in CAE. To improve the spot weld fatigue life correlation, extensive study has been carried out on the approaches used for calculating spot weld fatigue life, namely force & stress-based approaches. This study highlights the limitations of force based approach and addresses the advantages of stress based approach. Standard Double Cup (DC) spot weld specimen has been used for correlation of test fatigue life with the force based and stress-based approaches. Good correlation improvement has been observed with stress-based approach with contact definitions between the panels. Deployment of stress-based approach with contact definition on BIW showed significant reduction in the CAE predicted failed spot welds. Overall activity will help in ensuring first time right design and faster design convergence.