The effect of orientation on the shock response of a carbon fibre–epoxy composite

The effect of fibre orientation on the shock response of a two-dimensional carbon fibre–epoxy composite has been studied using the technique of plate impact. In the through-thickness orientation, it appears that the material behaves as though it is a simple polymer. When one of the fibre directions is orientated parallel to the loading axis, very different behaviour is observed. The stress pulse has a pronounced ramp, before at sufficiently high stresses, a much faster rising shock occurs above it. Examination of the wave velocities suggests that the start of the ramp travels at a near constant velocity of ca. 7.0 mm μs⁻¹, whilst the shock velocity in this orientation converges with that of the shock velocity of the through-thickness orientation. Therefore, we believe that the stress pulse is separated into a fast component that travels down the fibres, with the rest travelling at the shock velocity in the matrix between the 0° fibres (epoxy plus fibres normal to the loading axis). Finally, from the Hugoniot, we observed that at low shock intensities, the 0° orientation was significantly stiffer than the through-thickness orientation. As the severity of the shock increased, the Hugoniots of the two orientations converged. Therefore, it would appear that orientation only effects the shock equation of state at lower shock stresses.