Structural Response and Damage Characterisation of NonCrimp Fabric CFRP Panels under Impact Loading

Abstract

Impact damage formation and resistance is of great importance to all designers of structural components whether mobile or stationary. This is particularly true in the case of composite materials where the lack of a local plastic deformation mechanism means that even small impacts can result in complete fracture of constituent members, accompanied with a substantial or complete loss of the load carrying capabilities in the region of damage. This paper presents the experimental approach used to examine the structural response and resulting damage in non-crimp fabric carbon fibre reinforced epoxy composite samples at varying strain rates. The strain rates considered are those associated with quasistatic, low-velocity impact, and highvelocity impact loading rates. The differentiating characteristics of these regimes is discussed, and their effect on the samples is shown through experimental damage characterisation including physical measurements and ultrasonic C-scans. It is found that there is a clear difference in the form of damage that occurs with a change in strain rate regime. Quasistatic and low-velocity impact loading produces similar damage levels to each-other at similar energies, and results in more extensive fibre fracture and permanent deformation. However, highvelocity impact favours interlaminar matrix failure (delamination), and also absorbs more energy at equivalent lower impact energy levels, producing more damage. The resulting conclusion being that damage from high velocity impact is harder to identify, and damage resistance for lower energy impacts decreases as impact velocity increases – even though the total impact energy may be equivalent.