A study is conducted to determine the plastic energy absorbed by a material subjected to cyclic loading during the crack propagation stage. The analysis is based on Liu’s elastoplastic solution for calculating the plastic energy around the crack tip combined with a modified crack propagation law. The plastic energy per cycle Δw is found to be dependent upon the fatigue crack length and therefore varies with the number of applied cycles. The mean value of this energy corresponds to the plastic energy obtained by measuring the area within the stress-strain hysteresis loops of the material under repeated loading. If fatigue damage is based on plastic energy, the trend of variation of Δw with the applied cycles in the present analysis shows that the application of the linear damage rule (such as Miner’s law) should be more successful in the low-cycle region than in the high-cycle region. This is consistent with experimental data.

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