Development of Fatigue Durability Analysis Techniques for Engine Piston using CAE

A piston in a diesel engine is subject to the high pressure and the high thermal load. The high structural reliability is required to the piston in the automotive diesel engine and it is important to confirm the design parameters of piston in initial design stage. There are lots of research works proposing new geometries, materials and manufacturing techniques for engine pistons. But, the failures of piston occur frequently in development stage. Failure mechanisms are mainly fatigue related. This paper presents failure mechanisms of the high cycle fatigue and low cycle thermal fatigue cracks which occur on the piston during durability test using engine dynamometer. In this study, FE analysis was carried out to investigate the root cause of piston failure. The analysis includes the FE model of the piston moving system, temperature dependent material properties, mechanical and thermal loadings. The results show that the crack on the flame position is caused by the stress amplitude during the full-load test. The crack at the rim on the thrust axes is due to the large compressive plastic strain amplitude generated in the thermal shock test. It shows a good agreement between numerical and experimental results.