The mechanical and thermal properties of several epoxy resins were mea
sured to obtain guidelines for the molecular design of an epoxy resin
for cryogenic temperatures. Two types of epoxy resin with different nu
mbers of epoxy groups were mixed (with different mixing ratios) and cu
red. Fracture toughness, flexural strength and thermal contraction of
the hybrid epoxy resins were measured down to cryogenic temperatures.
The results suggest that epoxies with larger molecular weights between
crosslinkings relaxed stress at the crack tip, even at cryogenic temp
eratures. Intermolecular forces and stress relaxation at the crack tip
were found to be important for high fracture toughness.