A new method for modelling the coalescence and growth of two coplanar short cracks of varying lengths in AA7050-T7451 aluminium alloy

The growth, interaction and coalescence of two coplanar short cracks of varying lengths in AA7050-T7451 aluminium alloy were studied under low amplitude cyclic loading. Fractographic studies showed that the way in which the fracture surfaces developed was dependent on the relative crack sizes, however interactions between the cracks did not significantly affect the crack growth rates before the tips of the cracks touch to form a single crack. Subsequently, the longitudinal growth rates of the crack were retarded for a period which appeared necessary for the newly coalesced crack to form a single semi-elliptical shape before resuming growth rates of a single crack. A new mathematical model was developed to account for this behaviour.

► Interaction of short cracks does not largely affect growth rates before coalescence.
► Upon coalescence, longitudinal crack growth rates were retarded for a period.
► Retardation period associated with the formation of a semi-elliptical crack shape.
► Extent of retardation is dependent on the ratio of paired crack lengths.
► A new mathematical model was developed for coalescence of coplanar short cracks.