A comprehensive, analytical treatment was presented of the micro elastic-plastic non-linearities resulting from the interaction of a stress perturbation with dislocation sub-structures and cracks that evolve during cyclic fatigue of wavy slip metals. The interaction was quantified by a material non-linearity parameter, β, extracted from acoustic harmonic generation measurements. The contribution to β from the sub-structures was obtained from the Cantrell model. The contribution to β from cracks was obtained by applying the Paris law to the Nazarov-Sutin crack non-linearity equation. The non-linearity parameter resulting from the two contributions was predicted to increase monotonically by hundreds of % during fatigue from the virgin state to fracture. The increase in β during the first 80-90% fatigue life was dominated by the evolution of dislocation sub-structures, while the last 10 to 20% was dominated by crack growth. Application of the model to Al alloy 2024-T4 in stress-controlled loading at 276MPa yields excellent agreement between theory and experiment.

Quantitative Assessment of Fatigue Damage Accumulation in Wavy Slip Metals from Acoustic Harmonic Generation. J.H.Cantrell: Philosophical Magazine, 2006, 86[11], 1539-54