

Fatigue of Glass Fiber Reinforced Polymer (GFRP) Strips Incorporating Carbon Nanotubes
Abstract
Fiber reinforced polymers (FRP) have been widely used as a retrofitting material for concrete and steel structures. Recently, carbon and glass FRP rebars have been replacing conventional steel reinforcement in many applications because of their high strength and corrosion resistance. A major challenge that limits the use of Glass fiber reinforced polymers (GFRP) is its poor fatigue performance. Structural design codes suggest limiting the fatigue design strength of GFRP to about 20% of its tensile strength thus making it a non-economical alternative. In this paper, fatigue behavior of GFRP with and without carbon nanotubes (CNTs) was experimentally investigated. GFRP coupons with 0% (neat), 0.5% and 1.0% CNTs were tested under cyclic fatigue loading to extract their fatigue strength. The fatigue maximum and minimum stresses were chosen as 50% and 5% of the ultimate tensile strength respectively. While conventional GFRP coupons ruptured at an average of 87,000 cycles, GFRP coupons with 0.5% and 1.0% CNTs passed a half million cycles without rupture showing increase in fatigue life of GFRP in excess of 475%. The addition of low proportions (0.5%) of CNTs proved to significantly improve the GFRP fatigue strength. Microstructural investigations showed CNTs to be well dispersed in the epoxy matrix. This increased epoxy shear strength and limited damage evolution which improved the fatigue strength of GFRP.