INVESTIGATION ON BEHAVIORAL MODELS OF TENSILE FRACTURE IN COMPOSITES REINFORCED WITH CORE-TWIST HYBRID (GL/PET) YARNS

摘要

Polymer composite fracture can be controlled using hybrid yarns due to their crack preventing mechanism. The origin of this mechanism lies in differences of fibers fracture stiffness and strain. Therefore, application of these fibers can delay failing time and change the fracture type. In this study, fiberglass was used as central reinforcement because of its high module and tensile strength, and polyester yarn with different structures as fiberglass cover in form of core-twist yarn because of its high elongation and toughness. Covering level of the core yarn was varied from zero to 1000 TPM. Hybrid yarns in the form of three layers unidirectional fabric wetted with unsaturated polyester resin were used as matrix. Also, cool curing system was used in fabricating composites and hybrid samples. The present article studies the influence of covering percentage and polyester yarn structure on physical properties of the fabricated composites. Strength tests on fiber direction and microscopic investigations on fracture surfaces showed that the tensile energy absorption and so the other mechanical properties of the hybrid composite reinforced with glass yarn, which in turn has been covered with spun polyester yarn, is a much better than the other composites. Investigations show that the fracture mechanism could be controlled better with increasing covering yarn twist (TPM), which in turn helps to prevent destruction of the sample. A fraction model can be provided to make five prediction fracture types through comparing fracture mechanisms of composite and hybrid samples.