Non-destructive infrared inspection of dry multilayer carbon fibre preforms

Thermography was used for performing non-destructive inspection of dry carbon fibre textile preforms used in manufacturing carbon fibre polymer-matrix composites (CF-PMCs). The aim was to probe the feasibility of identifying defects in thick carbon fibres preforms made from multiple layers of industrial textile reinforcements, before composites are manufactured. Inspecting dry preforms will not replace the inspection of final CF-PMC parts but it can avoid costly and wasteful manufacturing of CF-PMC parts from defective preforms, as the defects sought in this paper cannot be observed by visual inspection. The preforms tested were made of two or four layers of industrial carbon fibre textile reinforcements. They featured defects of different widths, types and orientations. Results show that thermography can identify defects in preforms successfully, and that detection is influenced by the orthotropic thermal conductivity of carbon fibres, by yarn and fabric architecture, by the relative orientations of defects and yarns, and by the number of layers.