Effect of joint geometry on the toughness of epoxy adhesives

Abstract

Abstract Increasing joint thickness was shown to increase the toughness of epoxy joints hardened with either tetraethylenepentamine (TEPA) or hexahydrophthalic anhydride (HHPA). The increased toughness was associated with a marked increase in macroroughness. An upper limit of joint thickness and hence toughness occurred because very thick joints could not be produced. Residual stresses developed during cooling from the curing temperature caused the latter to separate at the interface. Stress corrosion cracking resistance was also found to depend on bond thickness. For the TEPA‐hardened system, bond thickness had only a minor influence for thicknesses up to 25 mils; and for the HHPA‐hardened system, this persisted to bond thickness of 50 mils. Further increases in bond thickness for both systems caused an abrupt rise in resistance to stress corrosion cracking.