Fatigue failure analysis and experimental research on the connecting rod of high-power marine diesel engine

Abstract

The connecting rod of high-power marine diesel engine fractured near the bolt hole before reaching the life expectancy, in which the typical fatigue fracture characteristics were found. The study improved the traditional simulation method of connecting rod to simulate the diesel engine more realistically. On the basis of the crank train model, various relevant boundary conditions are considered by introducing membrane mesh. The simulation results are consistent with the failure analysis of diesel engine, which verifies the correctness of simulation method proposed in this research. The material used for the connecting rod is 42CrMoA, which fatigue performance can only be obtained through fatigue testing. The yield limit of the material is 950MPa and an exact S-N curve is obtained by the fatigue test. This paper combined the material fatigue property with dynamics simulation, and found that the minimum safety factor of connecting rod occurs 5°CA after the TDC and is 1.33, which is satisfied but not sufficient. Meanwhile, the relationship between the bolt preload force and the stress level was investigated as the damage of connecting rod appears in the bolt hole region. Various preload forces were analyzed and the safety factor increased from 1.33 to 1.97 when the preload force is set to 80kN, which increased by 43%. In addition, the influence law between preload force and stress as well the empirical formula between them were summarized. This research not only provides a new method for the selection of preload force, but also allows rapid analysis of the connecting rod stress without complex finite element models in the conceptual design stage.