Structural Bending Behaviour of an All-Composite Wing-Box with Delamination

Carbon-fibre reinforced structures are more and more used in aerospace due to their excellent mechanical properties and their sig-nificant weight reduction. However, due to their complex damage mechanisms, composite structures can have significant local reduction in strength which can influence the global structural behaviour. Among the different failure mechanisms, the delamination between two adjacent fibre reinforced layers of a laminate, caused by a low velocity impact threat, can be very dangerous especially under compressive loading conditions. If a delami-nation exceeds a certain size, it will progres-sively grow under the service load conditions. The resulting loss in strength and stiffness may cause the premature failure of the dam-aged component. In order to characterize the on-set and the growth of the impact induced delaminations in wing-box composite stiffened panels, an in-tegrated numerical tool has been developed within the ANSYS FEM code. Starting from the impact energy and im-pact location, the delamination size and loca-tion along the panel thickness is found by means of the Davis & Zhang procedure [1]. Then, a geometrically non linear analysis is carried out on the panel with delamination so as to find its residual strength. The delamination growth is taken into account using an Energy Release Rate based approach. The delaminated area has been modeled using shell elements placed in the mid-planes of the sub-laminates and the Energy Release Rate has been calculated by means of the Virtual Crack Closure Technique [2] for shell elements which has been implemented in the ANSYS FEM code. Finally, a sensitivity analysis has been performed to evaluate the influence of the impact energy and the impact location on the residual strength of the wing-box composite stiffened panels under investigation.