MICROEXTENSOMETRY, THE PEEL TEST, AND THE INFLUENCE OF ADHEREND THICKNESS ON THE MEASUREMENT OF ADHESIVE FRACTURE ENERGY

A series of small peel specimens made from a toughened epoxy adhesive and aluminium adherends have been used for measuring the peel force as a function of adherend thickness. These results have been used in con junction with a recent analytical model in order to determine the frac ture energy, and show how it changes as a result of different crack pa ths within the adhesive. In-situ SEM microextensometry has also been u sed to determine the in-plane displacements and strain during peeling, and to monitor the propagation of the crack path as a function of adh erend thickness. It is proposed that at least one of the mechanisms re sponsible for the measured changes in fracture energy, over and above any contribution due to adherend plastic dissipation losses, is the in fluence of the carrier cloth on the stress distribution within the adh esive bond. It is believed that the carrier cloth creates a stress con centration within the adhesive, creates a load shadowing influence at the adhesive/adherend interface, and thereby precipitates cracking awa y from the interface and in the adhesive. (C) 1998 Elsevier Science B. V. All rights reserved.