Unidirectional plyUD

A bundle of thousands of continuous carbon filaments handled as a single unit, the carbon fibre equivalent of a glass roving. Tows are designated by their filament count in thousands, written with a K, and are used directly in filament winding, automated fibre placement and weaving.

Reinforcement fibre pre-impregnated with a controlled quantity of resin, usually a partially cured (B-staged) thermoset, supplied in rolls and stored chilled or frozen until layup. Prepregs give precise fibre and resin content and are the standard material form for high-performance aerospace and motorsport laminates.

The waviness introduced into fibres where yarns pass over and under each other in a woven fabric. Crimp reduces the stiffness and compressive strength the fibres can deliver, which is why non-crimp fabrics and unidirectional tapes are preferred for highly loaded laminates.

The main unidirectional load-bearing element running along the length of a wind turbine blade or wing spar, carrying the principal bending loads. Spar caps are typically thick stacks of unidirectional glass or carbon laminate, or pre-cured pultruded planks bonded into the structure.

The specified order and orientation of the plies through the thickness of a laminate, usually written as a shorthand code of ply angles. It governs the laminate's stiffness, strength and coupling behaviour, and is fixed on the drawing as part of the laminate schedule.