The fracture toughness and stress corrosion cracking characteristics of an anhydride‐hardened epoxy adhesive

Abstract

AbstractThe toughness and stress corrosion cracking characteristics of an epoxy resin (DER 332) hardened with hexahydrophthalic anhydride (HHPA) were investigated. The epoxy was studied in both the bulk and bond form, and its properties were compared with an amine‐hardened (tetraethylene pentamine, TEPA) system. The toughness, 𝒢Ic, of the anhydride system varied less as a function of ratio of hardener‐to‐resin content and postcure temperature than it did in the TEPA‐hardened system. Like the latter, however, its toughness in the bulk and bond forms could not be correlated, but 𝒢Ic of the joints was dependent on tensile modulus and/or yield strength of the bulk epoxy. Both systems were also toughened in the vicinity of the crack tip by water for short‐time loading, but their long‐time load carrying capability was reduced by a water environment. The anhydride hardened system was more sensitive to strength loss in water than the amine system. The fracture morphology for the two systems was the same, i.e., fast cracking occurred cohesively near the center of the bond, and slow cracking occurred at the interface.