Al-Si piston alloy behavior under combined mechanical and thermal cyclic loading with superimposed high -frequency thermal cycling

On pistons for diesel direct injection engines, the thermally high loaded bowl rim is exposed to high-cycle mechanical and high-cycle thermal loading during each combustion event in addition to the thermal cycling induced by variable engine loading, e.g. between idle and full load. This combined loading at various overall temperatures during engine operation contributes to material damage and finally to a limited service life. In the past, the high-cycle thermal loading has neither been experimentally investigated nor incorporated into a numerical model for lifetime estimation. The work described in this paper deals with the setup of an experimental test procedure on samples taken from components for which the effects of slow temperature cycling, fast temperature cycling and mechanical cyclic fatigue loading can be combined in different ratios. The aim of the investigation is to characterize the sample lifetime with respect to varied test conditions in order to differentiate alloy- or process-related material variations in support of process and material development.