A two-dimensional elastoplastic finite element method (FEM) program was developed for analysis of cyclic deformation around the fatigue crack tip under variable amplitude loading. Edge fatigue crack growth in a thin rectangular AlCu4MglMnl plate under repeated tensile loading with a single 50% overload cycle was modeled. The computations show in detail the specific effects of an overload leading to the delayed retardation of the crack.

Results of the analysis were used for a direct estimation of crack growth rate according to Sih's energetic theory. A concept of “dead cycles” without crack advance was introduced to eliminate the influence of an unrealistically large crack jump in a model cycle. The crack growth rate was computed from the strain energy density change in the dead cycle and from the critical strain energy density resulting from low-cycle fatigue tests. For constant amplitude loading, the theoretical crack rate approximately agrees both with the experiments and with the crack rate determined from the crack opening stress by the ΔK_eff method.