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85 commonly be some type of fibre or particulate. At the moment, glass, carbon and aramid fibres such as Kevlar are the most frequently used. The matrix material is usually a polymer, resin, metal or ceramic. Ceramics produce the highest strength and stiffness but are brittle; metals are also strong and stiff, but ductile. Polymer and resin systems, or thermoplastics and thermosets, are the lightest, and are therefore the most widespread in unmanned vehicle and systems manufacturing. The reinforcement materials can be arranged in a continuous or discontinuous pattern. The latter typically involves fibres that have been chopped and randomised before being bound together in resin. There have been major improvements in randomising the fibres, to prevent pre-orientation of the reinforcement from influencing the machining properties of the material, over the past few years. Discontinuous fibre systems can also be made in 3D shapes, using additive manufacturing techniques such as selective laser sintering, where more complex parts than 2D or 2.5D (or ‘pseudo-3D’) are needed. By contrast, continuous fibre arrangements are not random. Instead they tend to come as either unidirectional (UD) material, which as its name suggests consists of fibres, tape or laminate oriented in a single direction, or as woven fabric with fibres oriented in multiple directions, typically at 90º to each other in a ‘criss-cross’ pattern. UD is the lightest and simplest fabric system, while the woven fabric type provides better specific degrees of strength and stiffness depending on where the loads on a structure are most likely to be. The assemblies of filaments or fibres used for producing UD or fabric can also come as rovings, tows or other bundles of varying sizes. Anywhere between 6000 and 12,000 filaments in a bundle is standard. Composites | Focus UD is the lightest and simplest fabric system, while the woven fabric type provides better specific strength and stiffness Unmanned Systems Technology | February/March 2018 Control systems for manufacturing composites have improved significantly in recent times, enabling more specialised materials to be offered for many niche applications (Courtesy of TenCate) The use of chopped fibre materials gives designers the freedom to conceive and develop complex, 3D solutions (Courtesy of A Schulman)