Fracture Toughness and Relaxation of Epoxy Resins at Cryogenic Temperatures

The relationship between fracture toughness and several epoxy resins has been investigated at cryogenic temperatures. Resins for cryogenic use are thought to require high fracture toughness at cryogenic temperatures. The fracture toughness and mechanical and dielectric relaxation of resins were studied at low temperature. The amount of plasticizer and molecular weight between crosslinks was varied. It was found that the fracture toughness had a close relation to the relaxation behavior, and hence, the effect of plasticizer disappeared at liquid helium temperature. The resin with larger epoxide equivalent had a higher fracture toughness even at liquid helium temperature. This suggests a guideline for the molecular design for the resin with high fracture toughness at cryogenic temperature.