Mechanical and thermal performance of magnesium carbon fiber sandwich composites with variable fiber orientations for...

Sandwich composites are broadly recognised for their excellent stiffness, strength, and durability while minimising their weight. This study investigates the fabrication, mechanical testing, thermal analysis, and microstructural characterisation of magnesium-carbon fiber sandwich composites for aircraft applications. The composite panels were fabricated using traditional methods such as filament drum winding, followed by hand layup and compression moulding with six stacking sequences, including unidirectional ([0°], [45°], [90°]), bidirectional ([0°/90°], [45°/-45°]), and multidirectional ([0°/90°/45°/-45°]) fiber orientations. X-ray diffraction (XRD) investigated phase composition and crystalline structure. Thermogravimetric analysis (TGA) revealed two-stage degradation, with [0°/90°]₄ retaining the highest residue (73-75%), followed by the quasi-isotropic laminate (69-71%), while [90°]₈ showed the lowest stability (51-53%). Differential Scanning Calorimetry (DSC) confirmed decomposition onset between 250 °C and 380 °C, with balanced laminates exhibiting reduced endothermic peaks. Mechanical testing revealed strong orientation dependence, with the [0°]₈ laminate exhibiting the highest tensile (223.8 MPa) and flexural strength (700.9 MPa), while the [90°]₈ configuration showed the lowest values. Impact behaviour contrasted with tensile and flexural results, where the [45°/-45°]₄ laminate absorbed the highest impact energy (0.42 kg·m; 101.43 kJ/m²). The quasi-isotropic stacking sequence Mg/CF[0°/90°/45°/-45°]2/Mg exhibited a well-balanced multifunctional response, attaining the third-highest tensile strength, second-highest flexural strength, and second-highest impact energy absorption among the evaluated laminates, while also demonstrating enhanced thermal stability as evidenced by higher TGA residual mass and more stable DSC transition behaviour. Microstructural analysis (SEM/EDS) revealed elemental composition and microstructural features, including fiber-matrix bonding, delamination, and fracture morphology. Results showed substantial differences in mechanical and thermal performance across fiber orientations, aiding in the design of magnesium-carbon fiber sandwich composites for lightweight, high-performance aerospace applications.