Void content

The proportion of a composite's volume occupied by fibre, a key measure of laminate quality and the main driver of stiffness and strength in the fibre direction. It is determined by methods such as resin burn-off, acid digestion or image analysis of polished sections.

Intermediate vacuum compaction of a partially completed prepreg stack, carried out periodically during lay-up to remove trapped air and seat the plies before further layers are added. Regular debulks reduce wrinkling, bridging and final void content, especially on curved tooling.

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 shear strength between the plies of a laminate, usually measured with a short beam shear test such as ISO 14130 or ASTM D2344. Low ILSS indicates poor fibre-to-matrix bonding or laminate quality, and correlates with susceptibility to delamination.