Evolution of Unstable Skin-Stringer Debonding Propagation in Composite Aircraft Structures: Implications on Damage Tolerant Design

Interlaminar damages are a key challenge that limits the widespread use of composite materials in aircraft primary structural parts. Although years have already passed since the introduction of these materials, unstable propagation of delamination damage is still the base for evaluating the durability and reliability of structures made of composite laminates. In this paper, the unsteady and sudden propagation of skin-stringer debonding in a typical aircraft composite panel is investigated. Experimental tests and advanced finite element simulations have been performed to assess the evolution of debonding under compressive loading conditions. Fibre-reinforced composite panels, reinforced with a single T-shape stringer and characterized by artificial debonding at the interface between skin and stringer, have been experimentally tested and numerically analysed. The test output has revealed unstable growth of the debonding, with implications for the structural stability of the panels. The experimental results have been then compared with numerical simulations performed by using the Virtual Crack Closure Technique based SMart-time XB numerical procedure and excellent correlation have been found in terms of strain measurements against compressive load.