Thermomechanical Behavior of an Automotive Exhaust Aftertreatment Application

An aftertreatment system is the back-end component of an automotive exhaust system, used mainly to reduce pollutant emissions. This system is exposed to high thermal loads which can exceed temperatures of 900 ^oC, usually they operate at temperatures under 600 ^oC - 700 ^oC, depending on the engine application. The durability assessment of a system under thermomechanical loads can be challenging due to the complexity of the technical problem, which involves complex material behavior at high temperatures and results in high thermomechanical strains and stresses. This study presents a computational approach for the lifetime assessment of an exhaust aftertreatment system subjected to thermomechanical loading. The method is composed of a fluid flow analysis to compute the temperature fields which are mapped to a mechanical analysis combined with a nonlinear elasto-viscoplastic material behavior. Lastly, the lifetime of the overall assembly is assessed through a fatigue analysis. The elasto-viscoplastic constitutive laws for the ferritic stainless steel EN 1.4509 are identified and a unified model for cyclic viscoplasticity based on the nonlinear kinematic hardening rule is implemented in ANSYS and the lifetime of the product is assessed. It is demonstrated how the lifetime of a product can be assessed by applying the afore mentioned computational approach. This method enables detailed prediction of strain and stress levels at high temperatures which using traditional test methods cannot be assessed. This computation approach will lead to shorter development time of products and will speed up its availability on the market.