The increased use of composite materials has been at the forefront of the tremendousincrease in weight efficiency of commercial aircraft in the last few decades. Along with their advantages comes a significant manufacturing challenge due to their susceptibility to the creation of defects within the composite during the process of creating the stiff and strong materials from flexible and deformable precursors.

One of the preferred manufacturing techniques for composite materials is the so-called pre-preg technology, where components are built up by laying sheets of fibrous plies impregnated with uncured resin. There are intermediate processing steps to reduce the inter-ply porosity, in which the uncured pre-preg stacks are consolidated under vacuum. The final step is to further consolidate and cure the part under a pre-defined heat and pressure programme in an autoclave. During these processing steps the resin goes through a number of chemical transformations, which results in major changes to its physical properties.