The lead crack concept applied to defect growth in aircraft composite structures

Currently, the cyclic fatigue growth and residual strength of damaged aircraft composite structures under operational loads is not fully understood. This leads to structures generally being designed to a no damage growth criterion with many knock down factors included to cover unknown/untested effects. Thus, full optimisation of composite aircraft structures is unlikely to be achieved under the no damage growth criterion. In 2009 the US Federal Aviation Administration (FAA) introduced a slow growth approach to certifying composite, adhesively bonded structures and bonded repairs which could improve the situation and is worthy of further investigation. In this paper the growth of some (limited) damage types available in the literature are reviewed and a framework proposed to address the damage tolerance assessment of these structures.