Interlaminar fracture toughness in multi-directionally wet-wound fiber board: Cross-structure and parallel alignment

Fiber-reinforced products, renowned for their superior mechanical properties, find extensive applications in aerospace, transportation, and other fields. Single-filament wound (SFW) products suffer from uneven stress distribution due to fiber cross undulations within the same layer, limiting fiber strength utilization. In contrast, multi-filament wound (MFW) products exhibit a parallel arrangement of fibers, which helps avoid stress concentration and enhances impact resistance. Given that interlayer fracture is a critical failure mode affecting product performance, the interlayer performance and fracture mechanisms of MFW products were investigated in this study. A novel specimen preparation method was introduced, taking into account factors such as the winding process, tension control, and resin content. The fracture morphology of the specimen was analyzed to elucidate the relationship between fracture behavior and the winding structure, layer density, and specimen thickness. Results show that the fracture toughness of 5-mm-thick SFW specimens is 28.49% higher than that of MFW specimens. The interlayer pore defects have a greater impact on samples with lower single-layer fiber thickness, where a 20% reduction in single-layer fiber thickness results in a 22.3% decrease in the average strain energy release rate. Decreasing the specimen thickness increases flexibility, facilitating crack propagation along defect areas.