Time, temperature and water aging failure envelope of thermoset polymers

Abstract

Epoxies and epoxy-based fiber reinforced polymers (FRP) are significantly affected by environmental impacts during their service life. Exposures to water, humidity, temperature and UV radiation are known to substantially influence the (thermo-) mechanical properties and durability of the materials. Design-relevant characteristics like strength, stiffness, or the glass transition temperature change with time. Therefore, expensive test campaigns are often necessary in advance of a structural design. Prediction models based on physical relations or phenomenological observations are typically required to reduce costs and increase reliability. Consequently, a combined methodology for fast prediction of long-term properties and accelerated aging purposes is presented in this work for a common DGEBA-based epoxy. Therefore, master curves are obtained by creep and constant-strain-rate tests under temperature and moisture impact. A combined time–temperature–water superposition and the Larson–Miller parametrization demonstrate that time-saving CSR tests and modeling can replace long-lasting creep testing. Resulting, the presented methodology allows to determine a polymer's entire (environmental) failure envelope in a relatively short time and with low testing effort.