Viscoelastic characterization of high performance epoxy matrix composites

Abstract Dynamic mechanical analysis, stress relaxation, and creep experiments were performed to characterize the viscoelastic properties of a basic unmodified epoxy (Hercules 3501‐6) and a modified multiphase epoxy (Hercules 8551‐7), which are commonly used as matrices in high performance composites. The Arrhenius and WLF equations and a modified Standard Linear Solid (SLS) Model were used to quantify the viscoelastic behavior below, above, and at the glass transition temperatures, Tg. Both the modified and the unmodified epoxy systems exhibited a single relaxation peak above ambient temperature. The Tg of the modified epoxy at full cure was 170°C, which is 50°C lower than that of the basic epoxy. The glassy moduli of these two resin systems were found to be comparable, but the rubbery modulus of the modified epoxy was much lower than that of the basic epoxy system. However, the viscoelastic behavior of these two systems and their sensitivity to time‐temperature may be considered to be quite similar if they are compared with respect to their corresponding glass transition temperatures.