Experimental and Numerical Study of CF/PEEK Composites in Laser-Assisted Tape Placement with Heated Tool Temperature Above Tg

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The optimisation of process parameters in laser-assisted tape placement (LATP) for CF/PEEK composites has been widely studied; however, controlling the final composite properties remains challenging due to the inherently rapid heating and cooling rates. In this work, a heatable tool was introduced during manufacturing to regulate crystalline morphology and associated properties by maintaining the tool temperature within the crystallisation range of the matrix. Raising the tool temperature to 200 °C increased the average spherulite size substantially and the crystallinity from 34% to 37%. Numerical simulations revealed that in conventional LATP (without a heated tool), the tape surface temperature decreases rapidly to ~220 °C upon exiting compaction by the roller. By contrast, with a tool temperature of 200 °C, the temperature drop was limited to ~285 °C, arising from the significantly reduced the temperature difference between the incoming tape and substrate before nip point. This enhanced thermal profile promoted polymer diffusion, reduced interlaminar void content, and improved crystallisation. Transmission electron microscopy further confirmed the formation of a distinct diffusion region at tool temperatures above Tg, characterised by intermediate oxygen and carbon concentrations between fibre and matrix. These microstructural changes in crystalline morphology, void distribution, and interfacial structure were found to strongly influence the mechanical performance, including interlaminar shear strength and fracture toughness of CF/PEEK composites. Such findings are expected to provide new insights into optimising the performance of CF/PEEK composites manufactured by LATP through controlled microstructure, by introducing additional energy sources to address the intrinsic rapid heating and cooling rates without requiring major modifications to the LATP process.