Lifetime Prediction of Nano-Silica based Glass Fibre/Epoxy composite by Time Temperature Superposition Principle

The incorporation of nano fillers in Fibre reinforced polymer (FRP) composites has been a source of experimentation for researchers. Addition of nano fillers has been found to improve mechanical, thermal as well as electrical properties of Glass fibre reinforced polymer (GFRP) composites. The in-plane mechanical properties of GFRP composite are mainly controlled by fibers and therefore exhibit good values. However, composite exhibits poor through-thickness properties, in which the matrix and interface are the dominant factors. Therefore, it is conducive to modify the matrix through dispersion of nano fillers. Creep is defined as the plastic deformation experienced by a material for a temperature at constant stress over a prolonged period of time. Determination of Master Curve using time-temperature superposition principle is conducive for predicting the lifetime of materials involved in naval and structural applications. This is because such materials remain in service for a prolonged time period before failure which is difficult to be kept marked. However, the failure analysis can be extrapolated from its behaviour in a shorter time at an elevated temperature as is done in master creep analysis. The present research work dealt with time-temperature analysis of 0.1% SiO₂-based GFRP composites fabricated through hand-layup method. Composition of 0.1% for SiO₂nano fillers with respect to the weight of the fibers was observed to provide optimized flexural properties. Time and temperature dependence of flexural properties of GFRP composites with and without nano SiO₂ was determined by conducting 3-point bend flexural creep tests over a range of temperature. Stepwise isothermal creep tests from room temperature (30°C) to the glass transition temperature T_g (120°C) were performed with an alternative creep/relaxation period of 1 hour at each temperature. A constant stress of 40MPa was applied during the creep tests. The time-temperature superposition principle was followed while determining the Master Curve and cumulative damage law. The purpose of a Master Curve was to determine the variation of compliance with respect to increase in time and temperature of the specimen. The shift factors at any reference temperature were determined by Arrhenius activation energy method at a far lower temperature than T_g (Glass transition temperature) and by manual shift method at a temperature near T_g (Glass transition temperature).