Low temperature moulding of adaptive composites with embedded shape memory alloy wires
The feasibility of using a low temperature liquid composite molding technique to produce smart composites with embedded shape memory alloys was investigated. The epoxy system of EPON 828 resin and DETA hardener was evaluated, with embedded NiTiCu shape memory alloy wires. For successful low temperature processing, the wires must be maintained below the austenitic start temperature, As, during processing and a suitable post-cure profile must be developed that results in a final epoxy glass transition temperature, Tg, that is above the peak activation temperature of the SMA wire. A cure of 24 hours at room temperature, followed by a two stage post-cure at 45°C for 6 hours and 75°C for 45 minutes, produced excellent results. This post-cure profile produced a final epoxy glass transition temperature of 97°C, and suitable mechanical properties. Stresses were evaluated during cure and postcure with clamped or unclamped SMA wires using Fibre Bragg Gratings. This progressive cure cycle generates composites with reproducible activation behaviour, even with unclamped wires.