Health monitoring in continuous glass fibre reinforced thermoplastics: Manufacturing and application of interphase sensors based on carbon nanotubes

In this study, a new approach for health monitoring of GF reinforced composites is presented by incorporating percolated carbon nanotubes (CNTs) into the composites interphase. This is achieved applying CNT-filled coatings to glass fibres (GF). Taking advantage of the electrical properties of CNTs, this allows a highly localized monitoring of the composites interphase.The approach is largely independent on matrix material and can be applied to thermoplastic or thermoset resin matrix materials with minor adjustments. The resistance of CNT-coated GF yarns shows a linear dependence on the yarn length and depends on the CNT weight fraction of the coating, as well as on the amount of coating on the GF yarn. Performing tensile tests in combination with simultaneous resistance measurements on CNT-coated GF yarns embedded in a polypropylene matrix, the interphase behaviour during mechanical loading is monitored, providing information on this specific area. This allows relating interphase failure or GF breakage to the resistance data and demonstrates the potential of this approach for health monitoring of GF reinforced composites.