Laminate

A single layer of reinforcement within a laminate, such as one sheet of prepreg, fabric or unidirectional tape. Plies are stacked at specified orientations to give the finished laminate its required directional properties.

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.

A laminate whose ply orientations and materials mirror each other about the mid-plane. Symmetry prevents coupling between in-plane loads and bending, so the laminate remains flat after cure instead of warping.

Separation of the plies within a laminate, caused by impact, manufacturing defects, fatigue or moisture ingress. Because it can spread unseen beneath an undamaged surface and sharply reduces compressive strength, delamination is a primary target of non-destructive inspection.

The process of placing reinforcement plies into or onto a mould in the specified sequence and orientation, by hand or by machine; also used as a noun for the resulting stack or its design. Hand layup with wet resin remains the basic process for GRP boat building and GRP roofing.