Structural Hybrid Layer for Critical Strain Detection in Composite Parts: A Multifunctional Approach

Abstract

The rapid expansion of composite structures in different fields such as aerospace and automotive industries has highlighted the need for a new generation of hybrid materials able to overcome the current limitations of traditional laminates. In particular, because of their intrinsic layered structure, composite materials are sensible to impact damage that can generate internal damage that, if not detected, can lead to critical failures over short periods of time. In this context, a multifunctional approach would guarantee an extension of the life of the composite part by intervening simultaneously on two different aspects: first, the weak out-of-plane properties of the laminate need to be enhanced by introducing an additional hybrid phase within the composite structure and second, critical loads and internal damaged areas need to be immediately detected by monitoring the variation over time of specific electrical properties measured on the same embedded hybrid phase. By operating on both fronts (mechanical and nonmechanical) a true novel multifunctional material can be developed, able to resist to harsh environments and guarantee in-situ structural health monitoring features. This work is focused on the development of a smart hybrid composite layer that can be used in traditional manufacturing procedures and it is obtained by embedding an array of metal wires (e.g. copper, steel and Shape Memory Alloys) at specific depths within the structure of a traditional fibres reinforced polymer (FRP). The correct location and specific nature of the wires was evaluated via a previous mechanical tests campaign in order to optimise the enhancement of the impact resistance, while the non-structural properties were tested by monitoring the variation of specific electrical properties (e.g. resistance and impedance) using innovative High Frequency NDT techniques. Results showed that by including the Structural Hybrid Layer within a traditional laminate it is possible to increase the total safety of a structure by enhancing its reliability and at the same time to reduce maintenance costs via in-situ SHM.