Remaining life prediction of cracked stiffened panels under constant and variable amplitude loading

This paper presents the methodologies for remaining life prediction of stiffened panels under constant and variable amplitude loading (CAL & VAL). Concentric and eccentric stiffeners have been considered. Stress intensity factor (SIF) has been computed using the parametric equations developed by conducting fracture analysis of stiffened panels utilizing numerically integrated modified virtual crack closure integral (NI-MVCCI) technique. Wheeler residual stress model has been employed to represent the retardation effects due to tensile overloads. Effect of various stiffener sizes and stiffener type (concentric and eccentric stiffeners) on remaining life has been studied under CAL & VAL. From the studies, it has been observed that the predicted life is significantly higher with concentric and eccentric stiffener cases compared to the respective unstiffened cases. Further, it has also been observed that the percentage increase in life is relatively more in the case of concentric stiffener case compared to eccentric stiffener case for the same stiffener size and moment of inertia. Expressions for remaining life have been proposed considering various loading conditions, type of stiffener and number of overloads. These expressions will be useful for designers to design the structural components/structures against fatigue and fracture.