The intrinsic toughness and adhesion mechanisms of a glass/epoxy interface

Glass/epoxy interfaces of sandwich specimens were fractured under steady-st ate conditions over a wide range of in-plane mode-mix. The plastic dissipat ion was calculated via finite element analysis and subtracted from the stea dy-state fracture toughness to obtain the intrinsic toughness of the interf ace. Mechanisms which contribute to the intrinsic toughness were found to i nclude the thermodynamic work of adhesion, local inelastic deformations and polymer chain pull-out, but their combined energy was only approximately 1 5% of the intrinsic toughness. Angular dependent x-ray photoelectron spectr oscopy of the glass surfaces after fracture revealed epoxy adsorbed to a de pth of approximately 3 nm. Cleavage of epoxy strands was found to be the mo st significant mechanism contributing approximately 40% to the intrinsic to ughness of the interface. (C) 1999 Elsevier Science Ltd. All rights reserve d.