A simplified finite element methodology for the structural assessment of an engine piston under dynamic loadings

The piston slap strongly affects the structural integrity of engine pistons. This phenomenon is caused by the dynamic effects of the piston secondary motions, both horizontal translation and tilting. This occurrence amplifies the contact forces between the piston and the cylinder liner if compared to the ones calculated by using simple kinematic analysis. A numerical approach is therefore mandatory. This paper presents a numerical methodology to predict the influences of piston secondary motions on the piston fatigue life. A combined Multy-Body/FEM strategy is developed to obtain truthful forecasts saving computational effort. First, Multi-Body simulations are performed to evaluate the piston secondary motions and the loadings involved. The most critical instants are retrieved and equivalent lateral accelerations are derived in order to prepare simplified quasi-static Finite Element models. Then, the stress field and the resulting fatigue safety factor distribution of the piston are obtained. The methodology reveals itself to be a useful tool to predict the fatigue life of pistons capable of limiting the computational effort and supporting the dimensioning of engine components during the early stages of the design process.