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Composite & Non-Metallic Materials
Fibres and matrices, fibre orientation and sandwich structure, damage detection and NDT, plus wood, fabric and transparencies.
Composite & non-metallic materials — summary notes
FreeMain ideas
- A composite combines reinforcing fibres in a matrix: the fibres carry the load, and the matrix (usually an epoxy resin) transfers load between fibres, sets the shape and protects them. The result is high strength-to-weight, freedom from corrosion and properties that can be tailored by design.
- Common fibres: glass (GFRP — cheap, radomes, fairings), carbon/graphite (CFRP — very stiff and strong, primary structure), aramid/Kevlar (tough, impact- and abrasion-resistant) and boron. The matrix is usually thermosetting epoxy.
- Fibre orientation is everything — a laminate is strongest along its fibres, so plies are laid up at 0°/±45°/90° to carry loads in several directions. Honeycomb sandwich panels (a light core between thin facesheets) give great stiffness for very little weight.
- Damage is often hidden: impact can cause internal delamination or disbond with barely visible impact damage (BVID) on the surface, plus moisture ingress. Composites are inspected by tap test, ultrasonic, thermography and X-ray — not by eye alone.
- Other non-metallics: transparent acrylic/polycarbonate windows (handled to avoid crazing and scratches), wooden structures (grain, moisture and glue integrity) and doped fabric coverings on older/light aircraft.
- ⚠ Exam trap: composite impact damage can be extensive internally while almost invisible on the surface — NDT is required, not just a visual check. And carbon fibre in contact with aluminium sets up galvanic corrosion that attacks the aluminium.
Solved examples
A CFRP control surface is struck by a ground vehicle. The surface shows only a faint mark. Why can it not simply be signed off as serviceable?
Carbon-fibre laminates can suffer extensive sub-surface delamination from an impact that leaves barely visible damage (BVID) on the outside. The load-carrying plies may be broken internally. It must be assessed by NDT (tap test/ultrasonic/thermography) against the SRM limits before any airworthiness decision.
Composites concept map
FreeComposite & Non-Metallic Materials
Composite materials quiz
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