Fracture and fatigue analysis of curved or kinked cracks near fastener holes

The finite element alternating method is an attractive and efficient method 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 has been used to solve various engineering problems in assessing the structural integrity of aging aircraft, this method does have some limitations on the modeling of MSD cracks. This alternating method can only model cracks with mode-1 fracture behavior and requires the cracks to be straight and propagate in a self-similar fashion. As a result, there is some concern if the alternating method can be applied for the case when some of the cracks enamating from the fastener holes are slightly kinked. In the present research, cracks from fastener holes with the initial kink angles of + 30” and 30” are studied. It is found that the fracture and fatigue life for slightly kinked cracks near the fastener holes can be very well approximated using the stress intensity factor for pure mode-1 behavior obtained by replacing the slightly kinked cracks with simple straight cracks. Henceforth, the alternating method can be used to model slightly kinked cracks with straight cracks, thereby simplifying various fracture and fatigue analyses.