Development of an Experimental/Numerical Validation Methodology for the Design of Exhaust Manifolds of High Performance Internal Combustion Engines

Several typical failure modes in the exhaust manifold of an internal combustion engine are commented on. In particular, thermal loading and the related thermal fatigue damage mechanism are addressed. The component under investigation is a cast exhaust manifold including the turbine involute. Finite Element simulations are performed, and a numerical methodology is presented to interpret and understand the observed failures, with the aim of developing a useful tool to virtually validate the component, before the manufacturing phase. The Finite Element analysis closely mimics the experimental validation procedure that considers several heating and rapid cooling cycles to simulate typical engine operating conditions. A static mechanical characterization at high temperatures of the materials involved is carried out, aimed at identifying a suitable alloy and its mechanical characteristics useful for feeding the numerical models. The developed design methodology proposes a damage criterion for thermal fatigue investigation, considering the elastoplastic behaviour of the material when subjected to high temperature cycles. In particular, the accumulated equivalent plastic strain range for a single thermal cycle (ΔPEEQ) is used, following the Ferrari expertise. The methodology appears to be well correlated with the experimental evidence, thus limiting the number of tests necessary for the approval of the component.