Detection of impact damage in CFRP laminates by means of electrical potential techniques

Quasi-isotropic samples of carbon fibre reinforced polymer composite 2 mm thick were manufactured and instrumented with an array of electrodes. The electrodes were used to introduce a DC current and to measure the resultant potential distribution on the top and bottom surfaces of the laminate. Instrumented samples were impacted at energies between 2 and 12 J, and the potential fields measured before and after the impact. The impact damage caused significant changes in local values of potential. Indications of the extent and severity of the impact damage could be best obtained by representing the data as contours of equi-potential change. There was excellent correlation between regions of potential change and impact damage as measured by ultrasonic C scan. The results of finite element calculations of potential change distribution on the surface of current carrying quasi-isotropic laminates containing delaminations of a range of sizes and locations were qualitatively similar to those obtained experimentally, but differed in detail. Results are discussed in terms of the differences between real impact damage and that which was simulated, and the likely performance of a damage detection system based on this principle.