Influence of Hybrid Co-wrapped Yarn Structure on the Energy Absorption and Crack Propagation Resistance of Fiber-Reinforced Composites

Hybrid cowrapped (CW) yarns were engineered to enhance the impact resistance and damage tolerance of fiber-reinforced composites. To achieve synergetic mechanical properties, fibers with different failure strains were combined using the cowrapping technique. Four different hybrid yarn configurations were produced, with polyamide (PA) 6,6 fibers wrapped around EG fibers at different twist levels. Low-velocity impact (LVI) and compression after-impact tests were conducted to assess impact response, perforation threshold, and the damage tolerance of composite laminates. CW yarn-reinforced composites exhibited a substantial reduction in crack propagation under LVI compared to those reinforced with side-by-side hybrid yarns, with reduction rates between 19% and 60% for impact energies from 5 to 15 J. CW yarns at 50 twists per meter demonstrated superior damage resistance, attributed to their specific microstructure. Furthermore, increased twist levels were associated with greater energy absorption in the composites. Observed toughening mechanisms included fiber bridging and inter-yarn microcrack deviation, which enhanced energy dissipation and damage tolerance. The plasticity of PA fibers in the wrapping configuration inhibited crack propagation and protected the E-glass fibers. The most damage-tolerant specimens maintained almost the same compressive strength as undamaged, attributed to plastic deformation leading to a pseudo-ductile behavior.