Valued for their lightweight, high strength-to-weight ratio, and energy absorption, sandwich composites were adopted across multiple industries. This paper evaluates the static and dynamic mechanical performances of sandwich configurations exploiting carbon fiber-reinforced polymer (CFRP) and quartz fiber-reinforced polymer (QFRP) composite skins bonded to hexagonal Nomex^® or compliant Flex-Core^® cores. Skin thickness varied negligibly; therefore, this study focused on skin type and particularly core architecture influence on mechanical behavior. Three-point bending and flatwise compression tests evaluated flexural stiffness, core shear strength, and core compressive strength. DMA analysis was used to characterize their temperature-dependent viscoelastic response through the storage modulus, loss modulus, and damping factor. QFRP/Nomex emerged as the optimal configuration achieving the highest flexural stress, outperforming CFRP/Nomex by 14%, while restricting strain to 2.4% (compared to 7% for CFRP). DMA (Dynamic Mechanical Analyzer) analysis showed that QFRP/Nomex exhibits the highest storage and loss moduli. Observing the energy at break, CFRP/Nomex^® sandwiches stand out in their ability to absorb 60% more energy than QFRP/Nomex^® before total failure occurs, showing an overall superior energy absorption of CFRP skins. Conversely, flatwise compression tests revealed that QFRP/Flex-Core^® excelled in yield and compressive strengths, outperforming CFRP/Nomex by 10% and 8%, respectively, due to superior elastic matching. DMA damping profiles confirmed that the geometric compliance of curved Flex-Core^® cell walls in conjunction with QFRP skins accelerates structural yielding under shear and viscoelastic energy dissipation prior to chemical softening. This work highlights that sandwich structure design critically depends on managing core architecture and skin-to-core stiffness mismatch.

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.

This study experimentally evaluates how various 3D-printed gyroid core materials influence the mechanical and thermo-mechanical performance of lightweight carbon-fiber-reinforced polymer (CFRP) sandwich structures. Three gyroid core configurations were considered: short-carbon-fiber-reinforced polyphthalamide (PPA-CF), continuous-carbon-fiber-reinforced nylon (ONYX-R), and nylon short-carbon-fiber-reinforced (ONYX), all combined with similar 0/90° carbon-fiber-reinforced polymer composite (CFRP) face sheets. The sandwich specimens were manufactured using a one-step co-curing process and characterized by flatwise compression, three-point bending, and dynamic mechanical analysis (DMA). The PPA-CF-CFRP sandwich configuration exhibited the highest flexural performance, with a maximum flexural stress of 148–156 MPa, approximately 39% higher than that of ONYX-R-CFRP, and the highest mean compression modulus of approximately 87 MPa. However, ONYX-R-CFRP achieved the highest mean compressive strength of 12.84 MPa, compared with 11.85 MPa for PPA-CF-CFRP. These findings indicate that the mechanical response depends on the loading mode and is influenced by the combined effects of the thermoplastic matrix, carbon-fiber reinforcement architecture, and the resulting structural characteristics of the printed gyroid cores. DMA revealed that the PPA-CF-CFRP sandwich achieved a storage modulus of ~9 GPa at 30 °C, outperforming the ONYX-R-CFRP configuration by approximately 70%. Conversely, ONYX-R-CFRP exhibited the highest damping capacity, with a maximum tan δ of approximately 0.16, about 60% higher than the PPA-CF-CFRP configuration. The ONYX-CFRP sandwich configuration displayed the lowest mechanical and thermo-mechanical performance, demonstrating that the stiffness, deformation capacity, damping response, and temperature-dependent mechanical behavior of these sandwich structures can be tailored through the selection of the additively manufactured core configuration.