Effects of Processing on the Mechanical Performance of GF‐PC Composites: A Multiscale Investigation

A robust fiber‐matrix interface is crucial for any composite system, with higher challenges in thermoplastic matrices compared to thermosets (reaction in composite level). Tailored sizing promotes interface efficiency, while the manufacturing method, often with solvents to manage thermoplastics' viscosity, may be crucial. This study focuses on the interaction between sizing and processing routes and their effects on the fiber‐matrix interface's mechanical performance, comparing sized and desized glass fiber unidirectional mats with a polycarbonate matrix, using solution‐based and melt (film stacking) impregnation. Performance is assessed under different load‐types and scales, through transverse tensile testing and micromechanical fiber push‐out. Any changes in pure polymer are attested via nanoindentation. Focused ion beam (FIB) is employed for precise micromechanical specimen preparation and post‐mortem analysis. Results show evident differences in macro‐scale (mode I interface load), where processing has a substantial impact on the desized condition with increased performance for the solvent route, while the effects are of much lower magnitude on sized ones (predominantly cohesive failure), where the melt‐impregnation route provides better performance. At microscale and mode II interface load, differences are less pronounced, with no shear‐driven interface failure, as high matrix ductility shields interface failure upon certain loading. These findings were also analyzed by FE modeling, as well as FIB‐assisted post mortem evaluation.