Bond Thickness Effect in Adhesive Joints and Its Significance for Mode I Interlaminar Fracture of Composites

TLDR: In this paper, the effect of constraining the crack-tip damage zone on the Mode I fracture of a toughened epoxy resin (BP-907) was studied systematically using the double-cantilever-beam (DCB) adhesive joint specimen and scanning electron microscopy (SEM).

Abstract: The effect of constraining the crack-tip damage zone on the Mode I fracture of a toughened epoxy resin (BP-907) was studied systematically using the double-cantilever-beam (DCB) adhesive joint specimen and scanning electron microscopy (SEM). While a broad bond thickness range was employed (5 33 μm the fracture energy exhibited dramatic variations with t that were shown to follow from the variations in size of a certain dimple-like morphological feature. In constrast, the arrest energy was fixed, in consistency with the unchanging morphology. The fracture behavior for t < 33 μm was equally interesting, now though because Gic was fixed while G 1 C a varied with t. These changes in failure conditions were accompanied by morphological changes; as t decreased from 33 μm, the failure locus shifted from the bond center to the metal/matrix interface, and the failure itself occurred by shear yielding. Similarities were found in the failure conditions of butt joint and DCB adhesive specimens, on the one hand, and in that of the latter and composite interlaminar fracture, on the other hand, which suggest an interrelationship among these three failure phenomena.