Electrical-based delamination crack monitoring in composites using z-pins

The in-situ, real-time detection of delamination cracks in composite materials using z-pins is reported. Carbon fibre-epoxy composites were reinforced in the through-thickness direction with different volume content (up to 4%) or material type (composite, metal) of z-pins. Z-pins can reduce the through-thickness electrical resistivity of composites by several orders of magnitude (up to similar to 10(6)), depending on their volume content and electrical properties. Z-pins create an electrically conductive pathway through the-thickness of the otherwise resistive composite material (with an electrical resistivity of about 1.25 Omega m). Mode I interlaminar tests performed under static fracture and cyclic fatigue load conditions reveal that z-pins can be used to detect delamination cracking via changes to the electrical resistivity. The sensitivity of z-pins to changes in the resistivity caused by crack growth is influenced by their volume content, electrical conductivity and interfacial bonding with the composite material. (C) 2017 Elsevier Ltd. All rights reserved.