Electrical properties of multifunctional Z-pinned sandwich composites

The use of z-pins to controllably increase the electrical conductivity and to detect damage in sandwich composites is investigated. Sandwich materials with polymer foam core or balsa wood core were reinforced in the through-thickness direction with z-pins made of metal (copper, titanium) or carbon fibre composite. The through-thickness electrical conductivity of the sandwich composites was increased by up to nearly seven orders of magnitude by z-pins, although the in-plane conductivity was not affected significantly. The increase to the through-thickness conductivity was controlled by the electrical properties, volume content and/or insertion angle of the z-pins. Due to the increased conductivity, z-pins were used for in-situ and real-time electrical-based monitoring of damage caused by crushing or skin-core interfacial debonding of sandwich composites. In addition, the z-pins increased the flatwise compressive strength and in-plane fracture resistance of the sandwich composites. It is demonstrated that z-pins can increase multiple properties concurrently, including the electrical and mechanical properties, and also provide the functionality for in-situ real time damage detection.