Unmanned Systems Technology 001 | UAV Factory Penguin C | Real-time operating systems | Hirth S1218 two-stroke twin | Base stations | ASV C-Enduro | Composites | Datacomms

66 to inspect large components in one shot. Laser shearography is also a technique readily suited to PMCs. Here, the composite’s surface is illuminated with a laser light, and an interference pattern is created where the laser is reflected. By interpreting this pattern via a camera, the system now has a known reference; a load is then applied to the component and the measurement taken again. The loading alters the interference pattern detected, and the two patterns can be compared to identify any non-uniformity in the surface. Inspection is not only relevant to the production of components but also in service monitoring, identifying damage or defects and validating any repairs made. Once a defect is identified, material is usually sanded away around the defect zone in decreasing circles as each fibre layer is removed, to form a cone centred on the defect, until it too is removed. A patch is then applied, by rebuilding each missing layer and bonding in the new reinforcing material. Such repairs are typically as strong and durable as the original component. Metal composites Although most of this article has discussed PMCs, given that they are probably the most widely applied, it would be remiss not to mention their metallic-based cousins. The broad principles of MMC construction remain the same – using a metallic matrix such as aluminium or titanium for durability and ductility, matched with a ceramic reinforcing fibre or particulate (typically alumina, silicon carbide or tungsten carbide, among others). Fibre-based reinforcements can be formed in fabrics, as with PMC materials, or may even be 3D woven into a pre-form. Molten metal is then cast into the reinforcing fibre pre-form, often with the assistance of high temperature and pressure to keep the material molten and allow complete infiltration of the pre-form. MMCs typically have a higher modulus and strength than the matrix alloy alone, although ductility may be lower. The specific properties are also increased, as the ceramic reinforcement materials usually have a lower density than the matrix alloy, and so the composite’s strength-to-weight ratio is improved. There are also potential applications of MMCs when considering a typical metallic casting process. For example, local reinforcing inserts can be added to critical high-stress regions such as flanges or bolt holes to improve the overall performance of the component at a relatively low cost. Conclusions Composites are a natural fit for unmanned vehicles, either aircraft, spacecraft or underwater vehicles, where space and weight are at a premium and good mechanical performance is essential. The materials available and the techniques for their manufacture and testing have steadily matured, to the point that they can be relied on in safety-critical applications without being overly costly. Any structural or mechanical component is a potential candidate for a composite material, although the application will of course dictate the material and manufacturing choices. For example, a composite panel that is likely to experience abrasion can use carbon for low weight and high strength, with an outer shell of tough aramid fibres. The list of potential applications is long, but suffice to say that composites are most useful if properly considered and the design optimised. Acknowledgements The author would like to thank Gilles Rocher of North Thin Ply Technology, Claire Baker and Jenny Hodgson of Tencate Advanced Composites, Lorenzo Marandola of M1 Composites Technology, Christian Borg of TeXtreme, Francesca Cuoghi of CRP Group, Jack Taylor of Composite Metal Technology and Scott Dyson of Premier Autoclaves for their input into this article. November 2014 | Unmanned Systems Technology Aluminium-based MMC structural component – note cutaway showing reinforcement fibres (Courtesy of Composite Metal Technology) Composite repairs can be achieved to aerospace standards (Courtesy of M1 Composites Technology)