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In this study, application relevant toughened epoxy-amine formulations were investigated regarding their mechanical behavior at low temperatures and compared to a non-toughened reference. The application-oriented resins are based on reactive diluent-modified diglycidylether of bisphenol A (DGEBA) which were tested at 22 °C and −50 °C in regard to their fracture toughness (KIC) and fatigue crack propagation (da/dN) behavior. The E′ and E’’ moduli and the corresponding glass transition temperatures Tg were determined via dynamic mechanical thermal analyses (DMTA) which also described the influence of the block copolymeric toughener on the epoxy resin network. The plastic zone size, calculated during crack propagation, reveals the temperature dependent toughener-matrix interaction. The prevailing energy dissipation mechanisms were correlated with the changes of E’. SEM micrographs confirm the superior performance of the toughened system at −50 °C by the decrease of the fatigue cack propagation slopes and highlight the trends of the materials low temperature behavior.
Hübner et al. (Sat,) studied this question.