Mechanism investigation on fatigue failure in threaded hole of the main bearing in high-strength diesel engine

Under the development trend of high-strength and high-load diesel engines, the reliability problem of its cylinder block is becoming more and more serious. Aiming at the problem that the main bearing threaded hole of the cylinder block often fails, it is necessary to clarify the failure mechanism. The study first carried out the fatigue test of the cylinder block and selected the failed cylinder block to carry out the material mechanical property test, the material metallographic structure, chemical composition analysis, and the analysis of the failure section morphology. Then the numerical analysis model of the virtual test was established and the assembly preload and simulated gas pulse load were considered. Finally, the fatigue strength of the main bearing was evaluated based on the critical plane method, and the effect of fatigue load on the failure in the threaded hole was studied. The results show that the fatigue test of the cylinder block has verified that the position of the main bearing threaded hole is prone to fracture failure and the repeatability is extremely high. The fracture surface shows typical high-cycle fatigue characteristics, and cracks are generated near the bottom internal tread of the threaded hole. The bottom internal tread of the threaded hole obtained by the numerical analysis is the most dangerous position, which is consistent with the actual cracking position. The failure mechanism is high cycle fatigue failure caused by the gas-dominated stress amplitude exceeding the bearing capacity of the material and structure.