The significance of indentation in the inspection of carbon fibre-reinforced plastic panels damaged by low-velocity impact

Low-velocity impact tests were carried out at different energy levels on th ree types of T400/934 angle-ply laminates, by means of an instrumented drop -weight apparatus. After impact, the indentation depth and the residual ten sile strength were measured as a function of impact energy. From the result s obtained and experimental data available in the literature, an indentatio n law, allowing for the prediction of the impact energy from the depth of i ndentation, was developed. This indentation law appears to have a quite gen eral applicability, being scarcely affected by fibre type and orientation o r matrix type. A previous formula, modelling the residual tensile strength decay as a function of impact energy, was proved to be capable of correctly predicting the residual strength results for all the laminates tested. Com bining the indentation model and the residual strength model, a closed-form model, explicitly correlating the residual strength and the indentation de pth, was obtained. The theoretical predictions were in very good agreement with the experimental results. It is shown that the new model assumes a sim ple analytical form for a given laminate, permitting material characterisat ion by a minimum amount of test data. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.