Study of Adherence of Elastomers by Cyclic Unloading Experiments

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Abstract
We have studied the time evolution of the contact area between a spherical punch and a half-space elastomer sample by means of a cyclic push-on/pull-off test. The contact area edge is assumed to be a crack tip which propagates in the interface, moving backward and forward. It is shown that the equation of the kinetics of adherence, proposed in 1978 by Maugis and Barquins3 G - w = wø(aT v), linking the strain energy release rate G, the Dupré energy of adhesion w and the function ø characteristic of the viscoelastic material tested, is valid if w takes two particular values. The first, w 1 depends on the initial contact time, the second, w 2 w 1, depends on the compression time. These values are calculated theoretically according to Johnson et al. 2 by measuring the contact area radius. Thanks to this kinetic law, we can predict the number of cycles needed for separating the materials in contact. Moreover, it stresses the fact that the rupture does not occur if the application time of the tensile force is below a certain critical value. The experimental data obtained with a spherical glass punch on the flat surface of a polyurethane sample reproduce the theoretical predictions faithfully.

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