Fatigue crack growth: Validation of the Kmax-ΔK approach using the GTN damage model

Abstract

Considering cyclic plastic deformation as the single damage mechanism behind the fatigue crack growth (FCG), the effect of the mean stress is null in the absence of crack closure. In this study, an additional damage mechanism was introduced, predicting the effects of the growth, nucleation and coalescence of micro-voids. Using a non-local damage model, the reverse plastic zone was identified as the fatigue process zone, allowing to establish a relation to calculate its size. Considering aluminium alloy 2024-T351, the predictions are in close agreement with the experimental da/dN-ΔK curves, for distinct stress ratios. The results highlight that the effect of Kmax on the FCG rate is small in the absence of crack closure. On the other hand, modelling the contact between the crack flanks, the effect of Kmax on the FCG rate is amplified, i.e. the ΔK-Kmax plots for a given da/dN presented a Kmax dominance zone. The developed model suggests a three-parameter approach: ΔKeff -ΔK-Kmax.