No abstract

Loading conditions and complex geometry have led cylinder heads to become the most challenging parts of diesel engines. One of the most important durability problems in diesel engines is due to cracks in the valves bridge area. The purpose of this study is thermo--mechanical analysis of cylinder heads of diesel engines using a two-layer viscoplasticity model. The results of the thermo-mechanical analysis indicate that the maximum temperature and stress occurr in the valves bridge. The results of the finite element analysis correspond with the experimental tests carried out by researchers, and illustrate cracks in cylinder heads in this region. The results of the thermo-mechanical analysis show that when the engine is running, the stress in the region is compressive, caused by thermal loading and combustion pressure. When the engine is shut off, the compressive stress turns into tensile stress because of assembly loads. The valves bridge is under cyclic tensile and compressive stress state and thus is subject to low cycle fatigue. After several cycles fatigue cracks will appear in this region. The lifetime of this part can be determined through finite element analysis instead of experimental tests. The viscous strain is greater than the plastic strain which is not negligible.

One of the main aims in the management of farm equipment and tractors is to decide their replacement, based on technical and economic conditions. The objective of this research was to determine the economic life time for John Deer3140, common in the Varamin Region of Iran. First the annual depreciation and interest were calculated considering the initial purchase price of tractor, and then the economic life was calculated based on repair and maintenance costs. Based on the results, the most suitable replacement age was obtained, which was eight years for John Deer 3140.