Evaluation of plastic deformation and prediction of thermal mechanical fatigue life of an Al–Si alloy piston for diesel engines

Abstract

AbstractIn this study, a three‐step prediction method was developed to predict the thermal mechanical fatigue (TMF) life of an Al–Si alloy piston: (1) establishing a relation between the plastic deformation and fatigue life under the temperature cycle of 100–350°C via a series of TMF tests of the aluminum alloy specimens; (2) computing the dangerous plastic deformation of the piston under the thermal shock condition of interest by numerical simulation; (3) estimating the life of the piston through taking the computed plastic deformation into the established relation. The effectiveness of the proposed prediction method was verified by thermal shock tests of the piston, and the prediction error is no more than 25%. The mechanism of piston cracking can be summarized as follows: the inhomogeneous plastic deformation induced higher tensile stress around primary Si particles and protrusions at the rim and then microcracks were produced at the protrusions under the dangerous tensile stress, and finally, macrocracks occurred. The life of the piston under the thermal shock load and combustion pressure is speculated to be shorter than that under the thermal shock load. Considering the effect of stress relaxation on plastic deformation, the long full‐load operation of the engine contributes to the piston cracking in T direction, while the long idling operation reduces the piston cracking tendency in T direction and increases the piston cracking tendency in F and R directions.