Interpretation of magnetostrictive sensor data in Mode 1 and Mode 2 of carbon fibre reinforced polymers

Structural health monitoring (SHM) of carbon fibre reinforced polymers (CFRP) provides a valuable way to assess the condition of these materials, which possess desirable traits, but exhibit little elastic failure. Further complications arise due to their multi component nature, which means they can fail in a variety of ways. High-fidelity magnetostrictive SHM technology exhibits higher cost when utilising top-end materials that contain rare-earth elements. At the expense of fidelity, cost can be reduced by using Fe-based ribbons and cheap transducers. This reduction in accuracy can be overcome by coupling a detection array with the development of specific detection schemes for each failure type to reduce signal complexity. In this work, we investigate the failure of CFRP coupons in Mode 1 and 2 failure, using FeSiB ribbons as the actuator either bonded between the CFRP ply or co-cured on the surface. During the measurement, a set of 4 pancake coils are used to measure the change in inductance, as the CFRP fails, thus demonstrating that this magnetostrictive-coil set-up can be used to measure cracks forming and propagating within the CFRP, hence it is a promising SHM system. For the first time, it is demonstrated that there is a correlation between the induction signal and the elastic energy stored within the CFRP coupon.