Finite element analysis of fatigue strength along the fillet on upper deck of cylinder block of diesel engine

Finite element analysis was carried out to evaluate the distribution of stress along the fillet on an upper deck of cylinder block during the operation of diesel engine. The dynamic stress by cyclic combustion was analyzed taking into account the equilibrium of force acting in the main body assembly and cylinder head bolts in addition to their relative displacement condition. Preliminary analysis was firstly carried out to evaluate the stiffness ratio of cylinder head bolt and the main body assembly. The ratio was used for the main stress analysis of cylinder block. The main analysis was conducted for test and prototype engines. Their specifications are almost same except for the tightening position of cylinder head bolt. The following results were obtained. The distribution of stress during operation was not axisymmetrically but varied depending on the relative location against the outline of cylinder block and cooling water jackets. The results also agreed with the measured stress values. The amplitude and mean of stress obtained by the present analysis plotted on the fatigue limit diagram corresponds to the presence or absence of crack initiation along the fillet of test and prototype engines.