Fatigue crack growth and life prediction of 7075-T62 aluminium-alloy thin-sheets with low-velocity impact damage under block spectrum loading

This paper developed a fatigue crack growth model considering the effects of load interaction and low-velocity impact (LVI) damage. Fatigue crack growth (FCG) accumulative method was established to assess crack growth life of aluminium-alloy thin-sheets with LVI damage under spectrum loading. To validate the proposed model, LVI tests of 7075-T62 aluminium-alloy thin-sheets were conducted, followed by post-impact constant amplitude tension–tension and block spectrum loading FCG tests. Experimental results indicate that there are two competing mechanisms for the effect of LVI damage on the subsequent FCG behaviour of aluminium-alloy thin-sheets. One is the retardation effect on the crack growth rate from the dented plastic zone caused by LVI, and the other is the acceleration effect from the stress concentration due to impact-induced geometric changes. The new FCG model achieves a good agreement with FCG results of post-impact aluminium-alloy thin-sheets and can capture the LVI damage effect, opening an avenue to predict FCG life of aluminium-alloy thin-sheets with LVI damage.