Resin percolation and intimate contact in fast processing of thermoplastic composites

Abstract

Fusion bonding of thermoplastic composites (TPCs) requires intimate contact before polymer interdiffusion and solidification can establish an interlaminar bond. The lack of such intimate contact results in voids or disbonds. This study shows through cross-sectional imaging and scaling analysis that percolation flow, rather than squeeze flow, of resin through fibers is the dominant mechanism to achieve intimate contact in rapid TPC processes such as automated fiber placement (AFP) and welding. A 1D intimate contact model based on resin percolation, derived from Darcy’s Law, is presented and compared to experiments. While this model proved effective in comparing processing conditions by adeptly capturing trends, it under-predicted resin content in samples processed using AFP with low pressure. The model was extended to high processing rates, suggesting the importance of heated tools and high processing pressures on achieving intimate contact.. In-situ high-speed imaging and ex-situ microscopy revealed void size and morphology based on AFP processing parameters. The results of this study can guide fast processing of thermoplastic composites.