The impact wedge-peel performance of structural adhesives

The impact wedge-peel (IWP) test is an International Standard (ISO 11343) m ethod that is employed to measure the resistance to cleavage fracture of st ructural adhesives at a relatively high test-rate of 2 to 3 m/s. In the pre sent work this test has been employed to evaluate the performance of a rang e of structural adhesives when used to bond either steel or aluminium-alloy substrates. Firstly, a novel test arrangement for performing these tests, using a high-speed servohydraulic machine, is described. Tests were perform ed at 10(-4) and 2 m/s and at test temperatures of -40 and 23 degrees C. Hi gh-speed photography was also used to investigate the failure of the IWP te st specimens. Both stable and unstable types of crack growth were recorded, with the crack propagating cohesively through the adhesive layer in all ca ses. The methods of data analysis recommended by the International Standard are critically reviewed, and some shortcomings are highlighted. Secondly, the results from the IWP test are then directly correlated to the measured values of the adhesive fracture energies, G(c), of the adhesives, which wer e determined using a fracture-mechanics approach. Finally, it is demonstrat ed that, from knowledge of the value of G(c) of the adhesive, coupled with a finite-element analysis of the IWP test geometry, the failure behaviour o f the IWP specimen may be successfully modelled and predicted. (C) 2000 Klu wer Academic Publishers.