Hanan S. Fahmy^1,, Sara A. soliman¹, Abo-El Hagag A. Seleem², Mohammed Y. Abdellah^{1, 3}, G. T. Abdel-Jaber^{1, 4}

This study investigates the effect of glass fiber-reinforced polymer (GFRP) skin reinforcement on the mechanical performance of epoxy-based sandwich panels with a rigid Extruded polystyrene foam core manufactured by hand lay-up. The panels were fabricated using Kemapoxy 150 RGL epoxy resin and bidirectional E-glass woven fabric, with the number of GFRP layers per skin varied from one to four while maintaining a constant core thickness. Mechanical characterization was conducted through unnotched tensile tests (ASTM D3039), and center-notched tension tests to assess fracture behavior and damage tolerance. The results indicate that increasing the number of skin layers significantly enhances tensile strength, flexural stiffness, and fracture toughness. The unnotched tensile strength increased by more than 600% when the number of layers was raised from one to four, accompanied by a transition from brittle failure to progressive, damage-tolerant mechanisms. Center-notched specimens exhibited up to a 360% increase in remote failure stress and achieved a maximum critical energy release rate (GIC) of 9.35 kJ/m² at three skin layers, indicating optimal notch resistance. Fractographic analysis using scanning electron microscopy revealed a shift from clean fiber fracture and core exposure in thin skins to extensive matrix cracking, fiber pull-out, and distributed damage in multi-layer configurations, which promotes energy dissipation and crack blunting. Overall, the results suggest that three to four GFRP layers per skin provide an optimal balance between strength, stiffness, and damage tolerance in Extruded polystyrene foam-cored sandwich structures, offering practical design guidelines for lightweight applications in marine, aerospace, and civil engineering sectors.

GFRP sandwich panels, Extruded polystyrene foam core, vacuum-assisted resin infusion, tensile properties, fracture toughness, center-notched tension