THERMAL AND MORPHOLOGICAL SKIN CORE EFFECTS IN PROCESSING OF THERMOPLASTIC COMPOSITES

During thermostamping, the processing method where preconsolidated laminates are preheated in an oven and then transferred to a 'cold' mould for forming and solidification, the transfer from the oven to the mould as well as the initial cooling upon contact with the mould surface may cause high and/or unbalanced cooling on the two sides of a part. These conditions generate internal stresses as well as corresponding morphological features. This work focused on analysing the morphology through the thickness of a part using our process simulated laminate (psl) technique, which allows evaluation of a laminate through its thickness in relation to the processing conditions employed. Specifically, the degree of crystallinity and storage shear moduli were examined as a function of thickness for balanced and unbalanced cooled peek/AS-4 process simulated laminates. The resulting curvature for the unbalanced cooled laminates was measured in order to estimate the process-induced stress level. A methodology is in place to assess the importance of these phenomena for a variety of manufacturing processes. Thus, this study reveals through both differential scanning calorimetry and dynamic mechanical analysis that pronounced thermal and morphological 'skin-core' phenomena may be induced in thermoplastic composite laminates by high production rate processing techniques. © 1990.