Detection of Delamination in a CFRP Laminate during Drilling by Electrical Impedance Method

Abstract

In this study, we attempted in-situ push-out delamination (POD) detection during drilling using an electrical impedance method. We measured changes in electrical impedance and the internal strain around a drilled hole to detect the onset of POD, and estimated the critical thrust force for POD. It was proved that the onset and propagation of large POD can be clearly detected by the electrical impedance method, whereas for small POD, the impedance change is relatively less clear. POD detection sensitivity was improved by using circular electrodes on the exit-side surface instead of ring-shaped electrodes. Furthermore, changes in electrical resistance due to workpiece removal and drill indentation load were also examined, and the impedance change was inferred to be caused by damage, material removal and piezoresistivity effect. Because POD does not always occur at the maximum thrust force, POD onset can be detected more reliably by using not only thrust force but also impedance signals.