An energy approach to crack closure

Abstract

Crack closure is analyzed using an energy approach whereby it is shown that crack closure does not completely shield the input mechanical energy to the crack tip at a load below the crack opening load P _op if the compliance below P _op is non-zero. An equivalent shielding stress intensity range is defined by the energy release rate against crack closure. From this energy standpoint, the true effective stress intensity range should be defined as ΔK _eff=K _max−χK _op, where χ is the shielding factor. The conventional definition (ΔK _eff=K _max−K _op) is equivalent to the new definition only when the compliance below P _op is zero such that χ=1, i.e., for a fully closed crack. The corrected ΔK _eff is found to be effective in correlating fatigue crack growth rates (FCGRs) generated in 8090-T8771 aluminum-lithium alloy with and without crack closure. In contrast, the conventional ΔK _eff fails to reconcile the FCGR data within an acceptable scatter band.