Equilibrium-equivalent structural stress approach to fatigue analysis of a rectangular hollow section joint

The equilibrium-equivalent structural stress method has been recently developed through several joint industry projects as a robust method to analyze welded components using finite element methods. This method has been proven effective in correlating a large amount of published fatigue test results in the literature. The authors employed this equilibrium-equivalent structural stress method for a competition organized by the SAE Fatigue Design & Evaluation (FD&E) Committee to predict the fatigue life of a rectangular hollow section joint. Among all the methods used by many participants, the authors’ life prediction was selected as the best, based on the actual test results. This paper provides the details of the SAE FD&E fatigue challenge problem definition, test results, and our structural stress approach. The predicted mean life by the equilibrium-equivalent structural stress method utilizing the proposed ASME Div. II Structural Stress curve was in excellent agreement with the actual mean life of the experimental results. Other stress indexes (such as the maximum principal stress and the von Mises stress) had maximum stress at a location different from the actual crack location. Furthermore, the equilibrium-equivalent structural stress showed significant mesh tolerance with only a few percent difference in stresses when halving the mesh size.