潍柴动力股份有限公司，山东 潍坊 261061
Abstract：In the view of the fracture problem of connecting rod′s big screw hole during fatigue test of a marine medium speed engine, the test process, fracture morphology and metallographic structure of fault parts are analyzed. The difference of fatigue calculation results between simplified global model and refined sub-model in finite element simulation are compared, the material of connecting rod is optimized and the extrusion thread process is improved. Finite element calculation and fatigue test are carried out for the improvement of the connecting rod. The results show that the main cause of the fracture is the insufficient fatigue strength at the threaded hole of the connecting rod. The simulation results of the sub-model agree well with the fault mode. The fatigue strength of connecting rod can be improved by improving mechanical properties of connecting rod and connecting rod adding process, the minimum safety fatigue factor is increased from 1.05 to 1.35, and the fatigue fracture of connecting rod can be effectively solved. The improved analysis can provide a reference for solving the problem that the same fault mode occurs in the thread of the key parts of the engine under cyclic load.
Keywords:connecting rod; fatigue fracture; fatigue safety factor; finite element calculation; sub-model