We demonstrated the localisation of impacts in orthotropic carbon fibre reinforced polymer (CFRP) composite materials to within a few centimetres, using a sparse array of fibre Bragg grating (FBG) sensors. This type of sensor is easily embedded in composites permitting the development of structures with integrated sensing capability. Impact location was determined by measuring the differences in time-of-flight of ultrasonic Lamb waves at three surface-mounted sensors. An algorithm was developed taking into account the angle dependence of the optical fibre sensor sensitivity and the variation of Lamb waves propagation velocity with direction and wave mode. The performance of FBG sensors for impact localisation was compared to that of standard piezoelectric transducers (PZTs), which are already widely used for that purpose. The FBG-based system showed promising potential for a non-intrusive impact detection system applied to self-healing composite structures.

We report the first measurements of self‐healing polymers with embedded shape‐memory alloy (SMA) wires. The addition of SMA wires shows improvements of healed peak fracture loads by up to a factor of 1.6, approaching the performance of the virgin material. Moreover, the repairs can be achieved with reduced amounts of healing agent. The improvements in performance are due to two main effects: (i) crack closure, which reduces the total crack volume and increases the crack fill factor for a given amount of healing agent and (ii) heating of the healing agent during polymerization, which increases the degree of cure of the polymerized healing agent.

Keywords: RTM ; flow monitoring ; internal strain measurement ; fibre Bragg grating ; sensors Reference EPFL-CONF-179067 Record created on 2012-06-29, modified on 2016-08-09

We report the first measurements of self-healing polymers with embedded shape memory alloy (SMA) wires. Improvements of healed peak loads by up to a factor of two are observed, approaching the performance of the virgin material. Moreover, the repairs can be effected with reduced amounts of healing agent. The improvements in performance of self-healing polymers with SMA wires are due to three effects: i) crack closure, which reduces the crack volume, ii) heating of the curing agent during polymerisation, which improves the cross-linking, and iii) mechanical registration of the two crack faces, which results in a reduced crack volume on closure.

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.