Abstract: The cyclic property of aluminium alloy sheet LY12-CZ is given quantitatively. Accumulated plastic hysteresis energy under cyclic loading is taken as damage criterion. Nonlinearity of damage accumulation with cycle number under cyclic loading is proven. The formula used to calculate instantaneous plastic strain energy is derived. The total dissipated plastic strain energy for the whole life period is calculated and its variation with stress range is shown. Fatigue damage is separated into two parts-static tension damage and cyclic damage. With the help of above analysis, a fatigue life estimation model is presented. Fatigue life estimations with the model of two stress level, four stress level and programed loading are completed. Comparison are made between calculated fatigue lives and the corresponding experimental data and the agreements are satisfactory.

Key words: fatigue damage, fatigue life, stress-strain hysteresis loop, cyclic hardenning, damage accumulation