Interlaminar bonding in thermoplastic composites: A comparative analysis of laser AFP and post-processing

Abstract

In-situ consolidation automated fiber placement of thermoplastic composites (ICAT) offers a promising alternative to traditional manufacturing methods, potentially reducing both cost and energy consumption. This study investigates the interlaminar bonding of carbon fiber/low-melt Polyaryletherketone (CF/LM-PAEK) composites using four routes: (1) ICAT at slow speed, (2) ICAT at fast speed, (3) annealing after fast ICAT above the matrix's cold crystallization temperature, and (4) compression molding (CM) after fast ICAT above the matrix's melting temperature. Rapid cooling and crystal formation during ICAT hindered polymer chain interdiffusion, resulting in suboptimal interlaminar properties (mode I and II fracture toughness, and short beam shear). Annealing after fast ICAT reduced voids and cold crystallized the quenched amorphous regions, thereby producing behavior similar to that of slow ICAT. Meanwhile, CM significantly reduced voids, redistributed fibers, and—due to slow cooling from the melt—enhanced fiber-matrix adhesion, albeit rendering the matrix more brittle. In contrast, ICAT samples displayed a more ductile matrix behavior but poorer fiber-matrix adhesion, leading to comparable mode I values yet reduced mode II and short beam shear properties. This study also incorporates ultrasonic inspection, density measurements, X-ray micro-computed tomography (μCT), and cross-sectional microscopy to statistically analyze void content and morphology, and their effects of interlaminar properties. Ultimately, these findings offer new insights into the interplay between processing and bonding—a key factor in optimizing interlaminar properties in thermoplastic composites.