Hojjat Ashouri - Sama technical and vocational training college, Islamic Azad University , Varamin Branch, Varamin, Iran

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 AZ91 cylinder heads of diesel engines. The threedimensional model of the cylinder heads was simulated in abaqus software and a two-layer viscoplasticity model was utilized to investigate the elastic, plastic and viscous behavior of AZ91 cylinder heads. The results of the thermomechanical analysis indicated that the maximum temperature and stress occurred in the valves bridge. The results of the finite element analysis (FEA) 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.

thermo-mechanical fatigue, finite element analysis, cylinder heads and valves bridge