This paper on "Thermomechanical Fatigue of Automotive Engines Cylinder Heads" was presented at the NAFEMS World Congress on The Evolution of Product Simulation From Established Methods to Virtual Testing & Prototyping - 24-28 April 2001, The Grand Hotel, Lake Como, Italy.

Abstract

In automotive industry, aluminium alloys are definitively used for cylinder heads, due to their low density, casting capabilities and good thermal conductivity. But, in engines with high specific power output, especially in the inter-valves area -the valves bridge- reached temperature levels induce several complex phenomena in the material behaviour near the « limits »: plasticity, creep, microstructural evolution. These phenomena determine the thermomechanical fatigue life (low cycle fatigue) of cylinder heads. Today, regular increase of both specific power output and fatigue life specification is encountered in industry.
In order to meet these increasing specifications and to reduce prototypes number, numerical models for thermomechanical fatigue life prediction are of great interest for new cylinder heads development. To be more accurate, these models must take into account complex phenomena in material behaviour.
In this paper, several models for cylinder heads aluminium material are presented, including a new model taking into account microstructural evolution connected to ageing. Conditions of application of such model in industrial development process are discussed, based on examples.