Thermo-mechanical analysis of fatigue cracks of diesel engines cylinder heads using a two-layer two-layer viscoplasticity model with considering viscosity effects

Loading conditions and complex geometry have led the cylinder heads to become the most challenging parts of diesel engines. One of the most important durability problems in diesel engines is due to the cracks valves bridge area. The purpose of this study is a thermo-mechanical analysis of cylinder heads of diesel engines using a two-layer viscoplasticity model. In this article, mechanical properties of A alloy, obtained by tensile tests at and C. Tensile tests were simulated by abaqus software and very good agreement was shown between experimental and simulation results of tensile tests. The results of the thermo-mechanical analysis indicated that the maximum temperature and stress occurred in the valves bridge. The results of the finite element analysis showed that when the engine is running the stress in the region is compressive caused by the thermal loading and combustion pressure. When the engine shut off the compressive stress turned into the tensile stress because of assembly loads. The valves bridge was under the cyclic tensile and compressive stress and then is under low cycle fatigue. After several cycles the fatigue cracks will appear in this region. The results of the thermo-mechanical analysis of cylinder heads correspond with the simulation results, carried out by researchers. Viscous strain was significant and its amount is not negligible.