Mechanical and Thermomechanical Response of Co-Cured QFRP Sandwich Structures with Additively Manufactured Fibre-Reinforced Gyroid Cores

This study investigates the mechanical and thermomechanical response of quartz-fibre-reinforced polymer (QFRP) sandwich structures incorporating additively manufactured gyroid cores. Three core variants were considered under the same nominal gyroid topology and 28% infill setting: chopped-carbon-fibre-reinforced polyphthalamide (PPA-CF), chopped-carbon-fibre-reinforced ONYX, and ONYX incorporating additional continuous carbon-fibre reinforcement (ONYX-R). Identical QFRP face sheets manufactured from woven quartz-fibre/cyanate-ester prepreg were co-cured directly onto the printed cores without a separate adhesive film. The resulting sandwich structures were characterized by flatwise compression, three-point bending, and dynamic mechanical analysis (DMA). Under flatwise compression, QFRP-ONYX-R exhibited the highest yield strength, 12.45 ± 0.16 MPa, followed by QFRP-PPA-CF at 11.70 ± 0.10 MPa, whereas QFRP-ONYX yielded at 2.00 ± 0.09 MPa. QFRP-PPA-CF exhibited the highest nominal maximum bending stress (131.55 ± 3.50 MPa) and apparent bending modulus (7.32 ± 0.07 GPa), while QFRP-ONYX-R showed an intermediate flexural response and QFRP-ONYX exhibited the greatest deformation capacity before break. DMA revealed a strong dependence of the apparent structural response on core configuration. QFRP-PPA-CF exhibited the highest storage modulus, approximately 8.4 GPa at 30 °C, and retained approximately 1.9–2.0 GPa at 160 °C. QFRP-ONYX-R displayed intermediate stiffness but the highest principal tan δ response, with peaks of 0.135–0.150 at approximately 97–100 °C, whereas QFRP-ONYX exhibited the lowest storage and loss moduli. Overall, the results show that, under a nominally similar gyroid architecture, core material and reinforcement strategy strongly modify compressive yielding, bending behaviour, apparent thermomechanical stiffness, and damping in QFRP-faced sandwich structures.