Fatigue Crack Growth Analysis of a Wing Stiffened Panel

Abstract

Cracking in the aircraft structure is a common phenomenon. If the cracks are unnoticed then, it may lead to catastrophic failure of the structure. Fatigue cracks will appear at the high tensile stress locations. Cutouts and fastener locations in the tensile stress field will experience high tensile stress because of the stress concentration. During its service operation, fatigue cracks initiate at critical locations of the airframe. These cracks grow under the variable amplitude service loading. If undetected and unrepaired, these cracks will grow to their critical sizes, which will result in a catastrophic structural failure. In the current study a stiffened panel from a wing of transport aircraft is considered. A wing box structure will be analysed to obtain the overall response of the structure for given loading condition. A local analysis will be carried out for a panel at the bottom skin with multiple stringers. The stress analysis of the stiffened panel is carried out to identify the fatigue cracking location. A variable amplitude service loading for a transport aircraft will be considered to derive the local stress history at the fatigue cracking location. A crack growth model under variable amplitude loading will be developed. This model will use the constant amplitude fatigue crack growth data in order to compute crack extension per cycle. Crack arrest capability of the stiffener perpendicular to the cracking direction will be established analytically. The required material fatigue crack growth rate is calculated.