Effect of Veil Interlayer Type and Placement on the Mechanical Response of Carbon and Glass Fiber/Epoxy Composites

ABSTRACT This study examines how five veil interlayer materials fine glass (FG), polyether ether ketone (PEEK), polyphenylene sulfide (PPS), polyetherimide (PEI), and polyimide (PI) affect the mechanical performance of carbon and glass fiber/epoxy composites when placed at two laminate positions (near‐surface, 8/2–1; near‐neutral axis, 8/2–2). Composites were fabricated by Vacuum Assisted Resin Transfer Molding (VARTM). Interlaminar shear strength (ILSS) and flexural properties by three‐point bending tests were evaluated per ASTM D2344 and ASTM D790 while the buckling response was evaluated under axial compression in a purpose‐built free‐clamped fixture and reported as the buckling peak force (BPF) at collapse. Fracture surfaces were examined by scanning electron microscopy (SEM). In carbon fiber composites, PEEK at the 8/2–2 position gave the highest ILSS gain (10.9%) and PEI at 8/2–1 produced the largest flexural strength increase (7.16%). The most pronounced buckling improvements came from FG veils at the near‐neutral axis: 17.33% for carbon and 34.83% for glass fiber systems. Near‐neutral axis placement (8/2–2) generally favored buckling resistance and often improved ILSS though material specific exceptions were observed; surface adjacent placement (8/2–1) was more effective for flexural strength in carbon fiber composites. SEM observations associated the performance gains with interfacial morphology, matrix retention, and mechanical interlocking rather than thickness or density changes alone. Carbon fiber composites showed larger ILSS and flexural strength improvements than glass fiber systems whereas the largest buckling gain was obtained in the glass fiber/FG configuration. These results offer practical guidance for veil selection and laminate positioning in composite interfacial engineering.