Low Velocity Edge Impact on Composite Laminates: Damage Tolerance and Numerical Simulations

Abstract

Composite laminates are increasingly being used in more complex structural applications where edges and cut outs are inevitable. These applications include wing skins of military and civil aircraft, further aerospace applications as well as automotive panels and critical structures. Composite components in such applications are highly susceptible to damage. Composites behave in a different manner to conventional metallic materials, which has introduced several design problems not previously encountered. One such problem has been the susceptibility of the material to accidental low energy impacts which frequently leave no visible mark on the impacted surface but considerable internal damage. Investigation of the residual strength and stiffness of composites after edge impact has become important for the design of aerospace components. Previously, the research work involved central impact of composite laminates but in this research we are investigating edge impact behaviour of composite laminates as parts of composite structures are particularly vulnerable to impacts, including near the edge of an inspection port or other aperture. Furthermore, impacts to such areas may lead to more severe damage near the edge of the laminate rather than the surface. Thus the present work extends these investigations to impact on the edge of composite laminates. The thesis includes both experimental investigations and finite element simulations of impact damage on the plane of the laminate near the edge (near-edge), and on the edge (on-edge) of composite laminates. A comparison with centre impact with on and near-edge impact is done to understand the damage on the edges and away from the edges. A new design has been developed and implemented to perform edge impact experiments. The research investigated the effects of various parameters like thickness, absorbed energies, force-time histories and damage behaviour of composite laminate. The damage size and mechanisms have been explored. Impact simulation was carried out using finite element code Abaqus. Explicit solution technique of the code was used to analyse the edge impact phenomenon. Results of the finite element analysis were compared with experiments. The residual strength of the laminates under compressive and tensile loading has been measured. Tensions after impact (TAI) tests were conducted to evaluate the residual load carrying capacity. The effect of edge impact on the low velocity impact response and the residual tensile strength is discussed via the test results. This thesis also includes computed tomography as the main technique for micro level damage characterisation and investigates the study of damage mechanisms of glass/epoxy laminates subjected to edge impact with varying energy levels and thickness. Computed Tomography aims to provide damage behaviour such as internal damage state, delaminations during different types of edge impact.