Health monitoring in continuous glass fibre reinforced thermoplastics: Tailored sensitivity and cyclic loading of CNT-based interphase sensors

In this study, we report on different approaches for tailoring the resistance as well as the sensitivity of interphase sensors based on carbon nanotubes (CNTs). The two main aspects in affecting their initial resistance as well as the sensitivity of the systems during mechanical loading are the yarn coating content and the CNT-weight fraction of the coating. Varying those factors, the conducted tensile tests show that the initial resistance as well as the sensitivity of the interphase sensors can be adjusted within a certain range. Additionally, it is shown that glass fibre (GF)-yarns with low coating contents allow identifying critical loads for the interphase, which are found to be below the ones for GF failure. Performing cyclic tensile loading above and below this critical stress value has a significant effect on the interphase life-time. In order to assess the interphase damage quantitatively, new parameters based on the resistance change are introduced. Those parameters allow for direct comparison and characterisation of different GF modifications, i.e. interphases, during mechanical testing by cyclic loading of the interphase sensors.