Mechanical and Thermomechanical Performance Evaluation of CFRP Sandwich Structures with Additively Manufactured Composite Cores

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.