Reliability Based Design and Inspection of Stiffened Panels Against Fatigue

This paper addresses the problem of developing optimum structural design and inspection strategy for fatigue crack growth in stiffened panels subjected to uncertainty in material properties and loading. The approach is based on the application of methods of structural reliability analysis. An optimization problem is formulated to minimize expected lifetime cost while maintaining a minimum acceptable reliability level. The effect of structural design and inspection schedule on operational cost and reliability is explored and tradeoff of structural weight and cost between load carrying structural members (skin and stiffeners) and inspections is conducted. The panel is assumed to be under plane stress condition, and stiffeners are modeled as rectangular bars discretely attached to the panel by fasteners. The stress intensity factor is first determined by enforcing displacement compatibility at fastener locations, fatigue crack growth rate is then obtained by numerical integration. Optimization revealed that improving the structure by designing it for multiple load path capability combined with the use of inspections can be very cost effective compared to unstiffened structure.

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