Molecular Simulation And Experimental Analysis On Elastic Modulus Of Swcnts/Epoxy Composites At High-Low Temperature

Carbon fiber/resin matrix composites are used in the aerospace field. Due to its application environment with wide range of temperature, the variation and correlation of microstructure and properties of resin matrix under high-low temperature need to be concerned in engineering application. The previous study found that a transition region of modulus occurred between fiber and matrix. When the fiber type and fiber volume fraction was constant, increasing the modulus of the matrix can reduce the shear stress concentration factor at the interface of the composite material effectively, so that the bending and shear properties of materials could be improved. Carbon nanotubes (CNTs) was used to improve elastic modulus of matrix at high-low temperature due to its excellent mechanical properties. To investigate the micro mechanism of the enhancing effects of CNTs is the key to guide designing composite materials with excellent mechanical properties. In this paper, for the problems above, molecular simulation and experimental analysis were used to investigate the change of elastic modulus with temperature between resin matrixes with different crosslinking structure and effects of CNTs on elastic modulus of resin matrix at high-low temperature. Moreover, the apparent results were analyzed from microcosmic aspects through simulation software. The main work is shown as follows:Two crosslinking unit cells of epoxy matrices, DDM/E51 and DDS/E51, were built through simulation software. On the basis of molecular dynamics simulation and experimental verification of glass transition temperature (Tg) the elastic modulus from cryogenic temperature until under the Tg were studied in depth. Both simulation and experimental results revealed that elastic modulus of the resin systems were decreased as the temperature increasing, similarly. The results were mainly due to a comprehensive effect of weaker segmental mobility, inferior segment packing density, lower cohesive energy density (CED) and higher free volume fraction at higher temperature.Crosslinking unit cells of single-walled carbon nanotube (SWCNTs) reinforced epoxy resin composite materials, S WCNTs/DDM/E51 and SWCNTs/DDS/E51 were built. Then both simulation and experimental results showed that the addition of SWCNTs improved the Tg and elastic modulus of epoxy matrix and reduce the coefficient of thermal expansion. Because the extremely rigid structure of SWCNTs played a critical role, which included limiting segmental mobility, increasing the cohesive energy density and the segment packing density, reducing the free volume fraction. The effect of SWCNTs on decrease of the free volume fraction and segment packing density above room temperature was very obvious, but in low temperature environment could be ignored. Otherwise, effect of SWCNTs on increase segment packing density of the epoxy matrix was almost same at different temperature.