Charpy and drop-weight impact response of Polyurea-coated glass fiber-reinforced composites and their post-impact flexural behavior

This study aims to systematically evaluate the influence of fiber orientation and polyurea coating configuration on the fracture toughness and post-impact mechanical performance of glass fiber-reinforced polymer (GFRP) composites. Laminates with fiber orientations of 0°, 15°, 30°, and 45° were fabricated via the hand lay-up method using a 12-ply E-glass fabric (300 g/m 2 ) with a nominal thickness of 3.5 mm to ensure a representative balance between stiffness, damage tolerance, and manufacturability. A portion of the laminates was coated in single- or double-sided configurations to enhance impact energy dissipation and surface damage resistance. Charpy, low-velocity drop-weight, and three-point bending tests were conducted to evaluate fracture toughness, damage resistance, and post-impact residual load-bearing capacity, while a two-way ANOVA was employed to quantify the effects of fiber orientation and coating type. In terms of performance, double-sided polyurea coatings increased energy absorption by up to 8.3%. Under low-velocity drop-weight impact, these coatings increased peak impact loads by up to 26.1% (reaching 17,141 N) and dramatically reduced the visible surface damage area by approximately 84.8% compared to uncoated laminates. Quantitative results from post-impact flexural tests revealed that double-sided coatings significantly enhanced damage tolerance, limiting strength loss to only 7–9% across all fiber orientations. Specifically, at 0° orientation, double-sided coated specimens retained 91% of their initial load capacity, whereas uncoated specimens suffered a drastic 56% strength reduction. These findings demonstrate that dual-side polyurea coatings markedly improve the residual structural integrity of GFRP composites by effectively mitigating impact-induced damage. Fiber orientation strongly influenced damage initiation and propagation in both Charpy and drop-weight tests; this effect was more pronounced in the Charpy impact response, while absorbed energy under drop-weight impact loading showed limited sensitivity to fiber orientation.