Failure Patterns and Post-Impact Tensile Strength of Bamboo Woven Epoxy Composites with Different Layer Configurations

Abstract

Natural fiber–reinforced composites are increasingly important as sustainable alternatives to synthetic composites, particularly for applications subjected to impact loading. This study investigates the effects of the number of layers and fiber orientation on failure patterns and post-impact tensile strength of black bamboo woven–reinforced epoxy composites. Composite laminates were fabricated using the hand lay-up method with one or two layers and different fiber orientations, including [0°/90°], [+45°/−45°], and hybrid configurations. The specimens were subjected to low-velocity drop-weight impact testing at an impact energy of 15 J, followed by tensile testing to evaluate their residual tensile strength and damage characteristics. The results show that both fiber orientation and the number of layers significantly affect damage distribution and post-impact tensile behavior. Two-layer laminates exhibited approximately 40–50% higher residual tensile strength than single-layer laminates. The [0°/90°/0°/90°] configuration demonstrated the highest load-bearing capacity and the smallest total damage area, with a post-impact strength reduction of only approximately 5%. In contrast, the [+45°/−45°] laminate experienced the greatest strength degradation, approximately 57–58%, due to extensive delamination and shear-dominated failure. In addition, the damage area on the bottom surface was consistently larger than that on the top surface, indicating tensile-dominated failure propagation through the laminate thickness. These findings indicate that increasing the number of layers improves post-impact tensile performance, whereas fiber orientation governs the dominant failure mechanisms and damage propagation behavior. This research provides practical guidance for designing impact-resistant and environmentally friendly composite laminates reinforced with black bamboo woven fibers.