DMA testing of epoxy resins: The importance of dimensions

Dynamic mechanical analysis is commonly used to characterize thermoset polymers at temperatures ranging from well below to well above their glass transition temperatures. Many sample fixtures are available; however, the best clamp and best sample dimensions for a given material are not often readily apparent. Five different epoxy amine networks with glass transitions spanning over 100°C were characterized on three-point bending, dual cantilever, and single cantilever clamps with both constant thickness and constant span-to-thickness. Glassy modulus values were accurately measured on all clamps provided span-to-thickness ratios >10 were maintained. Thermal expansion and decreasing sample stiffness with increasing temperature greatly affect measurements in the rubbery region resulting in single cantilever clamps being best suited to measure rubbery data.