Fretting fatigue optimization of piston skirt top surface of marine diesel engine

Abstract

Composite pistons are often used in highly rated marine diesel engines. Fretting usually occurs on the mating surfaces of piston crown and skirt due to alternating loads. A finite element contact model is introduced to calculate the temperature and stress distribution in the composite piston of a marine diesel engine. The Archard model and Smith–Watson–Topper parameter (a prediction parameter of fretting fatigue, also called SWT parameter for short), which is used as fretting wear and fatigue criteria, are calculated according to the stress and strain variation and relative slip on the contact surface. The model has been validated by previous cylindrical–flat contact experiments. The effects of shape of contact face and pretension of bolts on fretting performance have been analyzed. To reduce the possibility of fretting failure of the composite piston, the expression of the generating line of the piston skirt contact surface has been designed by Theory of elasticity. The parameters of the generating line have been optimized with nonlinear sequential quadratic programming and finite element mesh updating method. The optimization results show that the fretting fatigue parameter SWT on the optimized contact surface can be reduced by more than 35.6%, which means the longer fatigue life of the pistons. Some suggestions for designing contact surfaces have also been proposed. In the end, the design was proved by durability tests of the engine.