Mechanisms of Adhesive Failure

In the peeling test of adhesive tapes as well as in other experiments for adhesive failure, the transition of failure modes from cohesive to interfacial has been observed by several workers in the process of increasing rate or decreasing temperature. It is accompanied by an abrupt change of adhesive strength. These facts cannot be explained by the failure mechanism based on a weak boundary layer. (It would be willful to assume two kinds of weak boundary layers). In this paper, the phenomena above referred to and the dependence of adhesive strength on rate, temperature, thickness, and some physical properties of adhesives are attempted to be explained rheologically. The author has proposed a simple model theory to interpret the so-called failure envelope of T. L. Smith, where viscoelastic substances were represented by Maxwell elements connected in parallel and appropriate criteria for failure were introduced to an element, which was considered a weak point in the substance (Zairyo (Materials) 17, 322 1968). In addition to this treatment for cohesive failure, the following new criterion is introduced to the same model; that is, interfacial failure occurs when the elastic work of deformation of the whole system reaches a critical value. The formulae obtained represent the observed behavior at least qualitatively. Other dependence of adhesive strength on the variables aforementioned and the mutual reduction between them are also discussed.