Spar cap

The upright laminate member joining the spar caps inside a wind turbine blade or similar beam-like structure, transferring shear between them so the assembly behaves as an I-beam. Shear webs are commonly sandwich panels bonded in place with structural adhesive.

Reinforcement in which virtually all fibres run in a single direction, supplied as dry tape, lightly stitched or bound fabric, or prepreg. Unidirectional plies give the highest stiffness and strength along the fibre direction but need supporting plies in other orientations.

A continuous process in which fibre reinforcement is drawn through a resin bath and a heated die, curing into a constant cross-section profile such as a rod, tube or structural section. It gives very high fibre alignment along the pull direction and suits long production runs.

A composite of carbon fibre in a polymer matrix, usually epoxy, offering very high stiffness and strength for low weight. CFRP is used for primary aircraft structure, motorsport chassis, wind turbine spar caps and bonded strengthening plates for existing buildings and bridges.

Deviation of fibres from their intended straight path, either in the plane of the ply or as out-of-plane wrinkles, introduced during layup, forming or cure. Waviness locally reduces compressive strength and is a significant quality concern in thick laminates such as wind blade spar caps.