The formation of fiber waviness during thermoplastic composite laminate consolidation

The occurrence of fiber waviness in thermoplastic composite parts may lead to a significant knockdown and part rejection rate. Fiber waviness may form during processing, as manufacturing of thermoplastic composite parts can be complex and the maturity of manufacturing technologies is still quite low, compared with thermoset composites.

The key phenomena that govern the formation of fiber waviness during manufacturing of thermoplastic composite laminates have been identified. As the tooling shrinks during cooling in the consolidation process, the tool displacements are transferred to the laminate via tool-ply friction. Consolidation experiments with a glass tool plate allowed for real-time observation of the formation of waviness during consolidation. The degree of fiber waviness is affected by the processing temperature, the tool coefficient of thermal expansion, and the coefficient of tool-ply friction. The latter is affected by the combination of release media; a release agent already decreases the tool-ply friction significantly, while a combination of release film and release agent decreases the coefficient of tool-ply friction by an order of magnitude.

The identified mechanisms have been incorporated in a basic analytical model to describe the formation of in-plane fiber waviness during the consolidation process, to help defining the processing window for the production of waviness-free laminates. Altogether, this work provides a fundamental basis for a waviness-free processing route for thermoplastic composite parts, which is especially of interest in the production of large structures.