Through-thickness sensing of single Z-pin reinforced composite laminates

This paper investigates the through-thickness sensing behaviour of carbon/BMI Z-pin reinforced composite laminates. The through-thickness electrical resistance (TTER) is used as the sensing variable. Electrodes are bonded to the Z-pin ends and the TTER is measured employing a sensor reading and analysing (SRA) system. The SRA system consists of a multiplexer, a digital multimeter, communication modules and a PC running the National Instruments LabVIEW program for the control of the whole system and the TTER data acquisition. The sensing capability of through-thickness reinforced laminates is characterised via single Z-pin bridging tests, carried out in Mode I and Mode II. The experimental results show that the whole Mode I pullout process of Z-pins can be monitored via the TTER variation. In mode II, no actual pullout occurs and the Z-pins experience failure while bridging the delamination. However, the Z-pin failure event is detectable as a sudden increase of the TTER. This study demonstrates that carbon/BMI Z-pins can be successfully employed in multi- functional applications involving simultaneous delamination bridging and structural health monitoring.