Influence of pre-tensioning high-performance yarns on the bending stiffness of textile composites

This study explores the stiffness enhancement in textile composites using four different fiber types: carbon, Kevlar, Vectran, and high-tenacity polyester (HTP). Pretension levels of 0.2, 2, 5, and 10 N were applied. A setup was developed to measure fiber stiffness. Results indicate that carbon fiber consistently demonstrates the highest stiffness across all pretenstionlevels, attributable to its high tensile strength and modulus. Kevlar fiber, although initially less stiff than carbon, exhibits the most substantial increase in stiffness, particularly between 5 and 10 N of pretension, reaching a peak stiffness of 33.8 at 10 N. Vectran fiber shows a gradual increase in stiffness, surpassing HTP but slightly lagging behind carbon and Kevlar. The rates of yarn-specific bending stiffness increase were measured as 0.168 for HTP, 0.054 for carbon fiber, 0.173 for Kevlar fiber, and 0.191 for Vectran fiber. The study highlights the importance of understanding how yarn pretension affects the bending stiffness of yarn-polymer composites, which is crucial for advancements in textile engineering. It was found that variations in the bending stiffness of HTP and carbon fibers significantly impacted the composite bending stiffness more than Vectran and Kevlar fibers under pretension during composite formation. High-stiffness yarns were less influenced by increasing pretension during composite fabrication. The study suggests utilizing yarn pretension to control the stiffness of textile/polymer composites and proposes individually tensioning and pultruding fibers or yarns in the polymer matrix before composite formation. A specialized setup for achieving this during the protrusion process is recommended.