FRACTURE AND FATIGUE ANALYSIS OF CURVED OR KINKED CRACKS NEAR FASTENER HOLES

The finite element alternating method is an attractive and efficient m ethod for calculating the stress intensity factor of cracks emanating from fastener holes such as the problem of multiple site damage (MSD) at the fuselage skin of aging aircraft. While the alternating method h as been used to solve various engineering problems in assessing the st ructural integrity of aging aircraft, this method does have some limit ations on the modeling of MSD cracks. This alternating method can only model cracks with mode-I fracture behavior and requires the cracks to be straight and propagate in a self-similar fashion. As a result, the re is some concern if the alternating method can be applied for the ca se when some of the cracks enamating from the fastener holes are sligh tly kinked. In the present research, cracks from fastener holes with t he initial kink angles of + 30 degrees and - 30 degrees are studied. I t is found that the fracture and fatigue life for slightly kinked crac ks near the fastener holes can be very well approximated using the str ess intensity factor for pure mode-I behavior obtained by replacing th e slightly kinked cracks with simple straight cracks. Henceforth, the alternating method can be used to model slightly kinked cracks with st raight cracks, thereby simplifying various fracture and fatigue analys es.