Characterization of the Mechanical and Thermal Properties, Including Fracture Toughness, of Epoxy Resin System DGEBA, POPDA (D400)

New measurements of fracture toughness are reported from 8 to 293 K of RAL-71a epoxy resin by the means of a three-point-bending tests (also called Single-Edge-Notch Bending, SENB) according to ISO 13586 or ASTM D5045-14. Tensile stress and modulus on the same resin system are reported between room temperature and cryogenic temperatures, as well as thermal expansion, cure shrinkage and a cure kinetics fit. It is highlighted that there is a large reduction in fracture toughness at temperatures below 77 K ( G _IC = 1.53 kJ/m ² at 77 K and 0.36 kJ/m ² at 8 K), whereas other mechanical properties show little change. It was observed that preparation of the crack tip in the epoxy specimens is critical to achieving repeatable values of fracture toughness with artificially high values observed if there are high residual stresses at the crack tip as noted in ASTM D5045-14.