Damage Tolerant Behaviour of Unstable Skin-Stringer Debonding Growth in Composite Stiffened Structures

“Damage tolerant” is nowadays the predominant design philosophy for composite aircraft components, driven by the ongoing need to reduce weight and consequently enhance fuel efficiency and performance. In this context, it is crucial to study damage propagation under the operational forces experienced by the aircraft during flight, with specific focus on the potentially unstable and dangerous nature of delamination growth, which strongly affect the structural safety of composite structures. This work presents an experimental campaign to investigate the damage tolerance capabilities of fibre-reinforced composite stiffened panels. The latter is composed of a single T-shaped stringer and an artificial interlaminar damage introduced at the interface between the skin and stringer. The manufactured panels have been subjected to quasi-static compressive experimental tests. The deformations and the delamination evolution have been monitored by using strain gauges and lock-in thermography system, respectively. Unstable delamination growth has been observed. The test results have been carefully analysed and discussed to contribute to the understanding of the damage tolerant behaviour of the aeronautical composite panels under critical loading conditions. Furthermore, finite elements simulations have been carried out considering a fracture mechanics based numerical method. Comparison between results in terms of delamination propagation has been performed. The numerical outputs have confirmed the sudden and unstable debonding evolution. The proposed experimental data gives a valuable contribution to the literature background on the delamination propagation in composite stiffened panel, focussing on the unstable nature of the delamination under realistic operating loading conditions.