The Manufacture of Hybrid Micro-Braids to Improve Composite Through-Thickness Conductivity and Achieve Multifunctionality

• Main Author: O'Keeffe, Caroline
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2022

In the aerospace and automotive industries, demand for lightweight, fuel-efficient designs have resulted in an increase in carbon fibre reinforced plastic (CFRP) structures. However, concerns regarding difficult-to-detect damage in CFRP and the risk of in-service failure restricted further application. Current methods for damage inspection require costly downtime, and in-service sensors incur a weight penalty and potentially introduce defects. The development of multi-functional composites is key to improving material performance beyond the purely structural, and further reduce structural mass and volume. The research aim was to manufacture and incorporate a reinforcing multi-material tufting thread and create a multifunctional composite by increasing mechanical performance and through-thickness conductivity (TTC). Two potential functionalities were investigated. The first, examined a fully integrated crack sensing capability by monitoring changes in through-thickness electrical resistance (TTER). The second, examined the susceptibility of a composite to inductive heating and investigated a new approach for composite thermoset curing and repairability. The study described the braiding of a hybrid multi-material tufting thread comprising carbon fibre tows and metal wires. The braided thread enabled multi-material hybridisation that was fully integrated into the structure. Crack progression was successfully monitored by assessing changes in TTER. The presence of the hybrid thread also aided the induction cure of thermosets by increasing thermal uniformity and reducing hot spots during curing. This research successfully demonstrated the manufacture of multi-material multi-functional reinforcement tufting threads. The hybrid thread provided an in-service fault detection method that addressed the parasitic nature of current probes without compromising on mechanical properties. It generated a sensing method that has been fully integrated within a composite structure with the potential to reduce servicing and inspection schedules. This study expanded material capability and has the potential to advance CFRP and composite use in industry.