Fatigue life study of spot welds

The resistance spot welding process is widely used in the automotive industry. This dissertation reviews the spot weld fatigue life prediction methods and discusses the advantage of the structural stress method (SSM) for spot weld fatigue life prediction. The goal of the present study is to further extend and validate the structural stress method to predict the fatigue life of spot welds of different materials, under constant amplitude loading of non-zero R-ratios and variable amplitude loading.; This study further refined the structural stress equation and suggested to use a nonlinear geometric finite element model for structural stress calculation. The finite element models for structural stress calculation are discussed and the procedures to predict fatigue life of spot welds using the SSM are outlined in the dissertation.; Fatigue tests were performed to validate the SSM to predict the fatigue life of spot welds of DQSK and HSLA materials under R-ratios of R = -1, 0, and 0.5. A method to use SSM to predict fatigue life of the spot welds under variable amplitude loading was developed and validated by experiments. Fatigue tests of spot welds of mixed thickness and mixed materials were also performed. Failure modes of the spot welds in various fatigue tests were studied. A possible life prediction methods for mixed thickness specimens is discussed. Finite element models and results for the cyclic strain ranges at spot weld joints and the stress intensity factors in through-thickness direction cracks are also presented in this work.