Determination of material constants for crack size dependence crack growth model

A crack size-dependence crack growth model was used to characterise the fatigue crack growth in AL 7075-T6 and AL 2024-T351 alloys. It is shown that the crack growth parameters K and a can be used to linearise the crack growth in regions I (elastic) and II (plastic) by plotting fatigue data linear-linear da/dN × a versus K3, where cubic stress dependency is assumed. A theoretical attempt was made to relate this crack size-dependence fatigue crack growth parameters to the strain-life relationship constants. A reasonably good agreement was achieved when comparing between the theoretical predicted and experimental determined material constants.