Moderation of thermoplastic composite crystallinity and mechanical properties through in-situ manufacturing and post-manufacturing tempering: Part 2 – Morphological characterisation

Abstract

The piecewise nature of Automated Fibre Placement for thermoplastic composite materials can lead to significant variations in polymer characteristics over the full part volume, in large part owing to differences in cooling rate from melt and the number of high-temperature cycles to which a given point is exposed. In this work, ion etching is used to remove amorphous material from laminate samples and expose the crystalline structure in the matrix. This structure is then assessed using electron microscopy for all material layers, providing insight into the distribution of amorphous and crystalline phases. This investigation assesses laminates produced using unheated as well as heated (145 °C and 220 °C) tooling surfaces to determine the impact on part crystallinity. Samples are also exposed to post-manufacturing tempering to evaluate its ability to alter part morphology without expensive autoclave or thermo-forming operations. The results reveal significant variation in the morphology of a single sample, with an increased tooling temperature acting to promote crystallinity and homogeneity within the part. Furthermore, a significant difference between the morphology of material layers and the boundary zone between adjacent layers is observed, providing insight into previously obtained mechanical properties.