Failure and Fractography Studies of FRP Composites: Effects of Loading Speed and Environments

Abstract

Advanced fibrous polymeric composites are one of the most successful composite material systems due to their wide range of advantages such as high specific strength and stiffness, fatigue properties and corrosion resistance. Composite structures undergo different loading conditions i.e. from static to dynamic during their service life. The polymer matrix is more susceptible to the environmental changes than the fiber and thus dominates the mechanical behavior of FRP composites. Polymers are characterized as visco-elastic materials that their mechanical properties are strain rate dependent or they are called as sensitive to the rate at which loaded. At higher crosshead speed due to shorter load assisted relaxation time, there is reduction in ILSS. The polymer gets more time for relaxation at lower crosshead speeds; as a result there is enhancement of ILSS values. Fracture processes at the crack tip are controlled by thermal relaxation time and mechanical relaxation. (At higher strain rates the heat generation was much faster than heat removal due to quasi-adiabatic heating which increases the fracture strain. In both the systems the locus of failure will shift from fiber polymer interface to the matrix itself that means instead of adhesion failure the predominating failure may be cohesive failure and that too shear cusp formation.)Implications of thermal conditioning most often lead an improved adhesion of the interface and/or increased crack density. These changes might lead further complications in accessing the failure mechanisms of FRP Composites.