Modeling of spherulitic crystallization in thermoplastic tow-placement process: spherulitic microstructure evolution

A numerical study on the evolution of spherulitic microstructures during crystallization of fiber-reinforced thermoplastic matrix, poly-ether-ether-ketone (PEEK), in a composite tow-placement process is presented. A model for spherulitic microstructure growth within a unit cell formed between adjacent fibers and at the interlayer surface is developed, by accounting for the spatial temperature variation and the temperature history resulting from hot gas torch heating during the process, as discussed in a previous work [Compos. Sci. Tech., in press]. Parametric studies are conducted to elucidate the effects of processing conditions, in terms of torch incidence angle, θ, torch exit diameter, D, torch distance to target, L, hot gas temperature, Tnoz, gas velocity, Unoz, line speed, V, and number of layers in tow substrate, Nlayer, on the crystalline microstructures. The range of average spherulite size corresponding to optimal processing conditions based on considerations of overall crystallinity is determined.