Abstract
Fatigue crack growth (FCG) has been studied for decades; however, several aspects are still objects of controversy. The objective here is to discuss different issues, using a numerical approach based on crack tip plastic strain, assuming that FCG is driven by crack tip deformation. ΔK was found to control cyclic plastic deformation at the crack tip, while Kmax has no effect. Therefore, alternative mechanisms are required to justify models based on ΔK and Kmax. The analysis of crack tip plastic deformation also showed that there is crack tip damage below crack closure. Therefore, the definition of an effective load range ΔKeff = Kmax − Kopen is not correct, because the portion of load range below opening also contributes to FCG. Below crack closure, damage occurs during unloading while during loading the crack tip deformation is elastic. However, if the maximum load is decreased below the elastic limit, which corresponds to the transition between elastic and elasto–plastic regimes, there is no crack tip damage. Additionally, a significant effect of the crack ligament on crack closure was found in tests with different crack lengths and the same ΔK. Finally, the analysis of FCG after an overload with and without contact of crack flanks showed that the typical variation of da/dN observed is linked to crack closure variations, while the residual stresses ahead of crack tip are not affected by the contact of crack flanks.
Highlights
Fatigue crack growth (FCG) has been studied for decades; several aspects are still objects of controversy
The numerical of the fatigue crack growth (FCG) wascapabilities performed with finite was adapted to theanalysis study of considering the excellent for the thein-house modeling of plastic element code
There is an effect of Kmax, since different crack growth rates are obtained for the same ∆K
Summary
Fatigue crack growth (FCG) has been studied for decades; several aspects are still objects of controversy. There is a general agreement about the complexity of crack tip phenomena, involving different mechanisms that depend on the material, geometry, and loading These mechanisms include crack closure, residual stresses, crack-tip blunting, crack branching, phase transformation, and environmental damage. The focus must be placed on the crack tip, where the damage responsible for FCG effectively occurs Other phenomena, such as crack closure, residual stresses, or material hardening, are secondary but are relevant insofar as they affect the main phenomenon. It is assumed that cyclic plastic deformation is the fundamental mechanism responsible for FCG This approach includes the effects of cyclic plastic deformation, and crack tip blunting, material hardening and plasticity-induced crack closure. Different classical issues of FCG are revisited, namely the effect of maximum and minimum loads, and the existence of damage below crack opening
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