Fracture toughness of rubber-modified epoxy adhesives: effect of plastic deformability of the matrix phase

The fracture toughness of adhesively bonded compact tension (CT) and bulk single-edge notched bend (SENB) specimens using rubber-modified epoxy resins was investigated in terms of the relation between the J-integral value and crack extension, whereby the rubber-modified epoxy resins allow to alter the plastic deformability by changing curing temperature. For the SENB specimen, the crack extension is very small and the J-integral value increases with enhanced plastic deformability. On the other hand, for the CT specimen, a considerable crack extension is observed, furthermore, when the crack extension is nearly equal to 0.2 mm, the J-integral value does not vary with curing temperature; however, the slope of the J-Deltaa curve slightly decrease with enhanced plastic defomablity. To elucidate these behaviors, assuming that the resins are governed by the Gurson's constitutive equation, the void-volume fractions near the crack tip of both the specimens were calculated by finite element method. It was found that the characteristics of J-R curves can be explained from the results of calculated void-volume fraction. (C) 2002 Elsevier Science Ltd. All rights reserved.