Modeling of stiffness of FRP composites under elevated and high temperatures

When subjected to elevated and high temperatures, the mechanical properties of FRP composites, such as the E-modulus and viscosity, experience significant changes. At a certain temperature, a composite material can be considered a mixture of materials that are in a glassy, leathery, rubbery or decomposed state. The mechanical properties of the mixture are determined by the content and the property of each state. The content of each state can be estimated by kinetic theory. A model based on the Arrhenius equation was developed to predict the temperature-dependent E-modulus, G-modulus, viscosity and effective coefficient of thermal expansion of FRP composites during the different temperature ranges, including the glass transition and the decomposition of the polymer resin. The kinetic parameters, such as activation energy and pre-exponential factor, were estimated by a modified Coats–Redfern method. The prediction of the temperature-dependent mechanical properties was compared with experimental results obtained by Dynamic Mechanical Analysis (DMA), and a good agreement was found.