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 ∼106), 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 Ω 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.