Elastic response of circular CFRP plates under low-velocity impact

Low-velocity impact tests were carried out on circular carbon fibre reinforced plastic plates made of in-plane quasi-isotropic laminates of different thickness, which were clamped along the periphery and struck at the centre by a hemispherical steel tup. The recorded force-displacement curves exhibited a clear non-linearity in the elastic range. To model the non-linearity observed, a closed-form formula accounting for large displacements, proposed for isotropic materials, was used. The formula was suitably modified, to take into account the tup displacement associated with indentation. Only two of the constants appearing in the analytical model were derived from the experimental data, whereas the others were calculated. A good agreement was found between the theoretical predictions and the experimental curves. The analytical model reveals that the laminate behaviour is dominated by the large displacements regime for thin plates, whereas local indentation becomes more and more important with increasing the thickness.