Probabilistic Isothermal, Anisothermal, and High-Temperature Thermo-Mechanical Fatigue Life Assessment and CAE Implementations

Fatigue life assessment is an integral part of the durability and reliability evaluation process of vehicle exhaust components and systems. The probabilistic life assessment approaches, including analytical, experimental, and simulation, CAE implementation in particular, are attracting significant attentions in recent years. In this paper, the state-of-the-art probabilistic life assessment methods for vehicle exhausts under combined thermal and mechanical loadings are reviewed and investigated. The loading cases as experienced by the vehicle exhausts are first categorized into isothermal fatigue, anisothermal fatigue, and high-temperature thermomechanical fatigue (TMF) based on the failure mechanisms. Subsequently, the probabilistic life assessment procedures for each category are delineated, with emphasis on product validation. Finally, two examples: an isothermal fatigue life assessment for a welded exhaust sub-system, and a high-temperature TMF life assessment for an exhaust manifold (base material) are provided to demonstrate the probabilistic life assessment procedure with the computer-aided engineering (CAE) and finite-element analysis (FEA) tools.