Fatigue life fracture analysis of the diesel engine oil pan edge structure

This study investigated the fatigue fracture failure at the edge connection of a diesel engine oil pan. The failure mechanism was elucidated through macroscopic and microscopic fracture analyses together with finite element simulations. The results showed that the crack originated from the high-stress concentration zone near the connection between the oil pan and the fastener, which is associated with the inherent geometric characteristic of the original structural design, and its macroscopic feature was a penetrating crack with a thickness of approximately 3 mm. Non-metallic inclusions identified in the crack-origin region, especially complex oxide inclusions, were considered important microstructural factors associated with crack initiation. Finite element analysis further confirmed a significant stress concentration in the edge region under operating loads. Overall, this failure resulted from the combined effects of manufacturing defects, structural stress concentration, and operational loads. Based on the random-vibration response, Goodman correction, Basquin relation, and Miner's rule, a macro fatigue-life assessment framework was established for the critical region of the oil pan. The assessment results indicated that the edge connection and local structural transition zone corresponded to the fatigue-critical region under the investigated condition. Structural optimization based on response surface methodology reduced the maximum von Mises stress of the oil pan by 18.3%. These results indicate that the proposed approach can effectively identify the critical failure region and provide a feasible stress-reduction strategy with the potential to improve fatigue performance.