An Energy Based Critical Fatigue Life Prediction Method

Abstract

The capability of a critical life, energy-based fatigue prediction method is analyzed in this study. The theory behind the prediction method states that the strain energy accumulated during monotonic fracture and fatigue are equal. Therefore, a precise understanding of the strain energy density behavior in each failure process is necessary. The initial understanding of energy behavior shows that the accumulated strain energy density during monotonic fracture is the area underneath the experimental stress-strain curve, whereas the sum of the constant area within every stress-strain hysteresis loop of the cyclic loading process is the total strain energy density accumulated during fatigue; meaning, fatigue life is determined by dividing monotonic strain energy density by the strain energy density in one cycle. Further observation of the energy trend during fatigue shows that strain energy density per cycle is not constant throughout the process as initially assumed. This finding led to the incorporation of a critical life effect into the energy-based fatigue prediction method. The analysis of the method’s capability was conducted on Al 6061-T6 ASTM standard specimens. The results of the analysis provide further improvement to the characterization of strain energy density for both monotonic fracture and fatigue; thus improving the capability of the energy-based fatigue life prediction method.