AN INTERNAL VARIABLE THEORY OF ADHESION

A model describing the flat contact with adhesion between rough solid bodies has been set up, in which the set of asperities is described as a third thin body. Due to the local compressive stresses, the cavitie s close up during compressive loading, leading to increased adhesion i n the contact area. An internal variable model describing the evolutio n of the intensity of adhesion in the contact between the two solids i s set up, based on the thermodynamics of irreversible processes. From a perturbation method, a material surface model for the third body is derived. The Hertz theory of the plane contact between solid elastic b odies is then modified in order to account for the increased adhesion when both solids are pressed together. The specific problem of the com pression of a rubber hemisphere on a glass plate is analysed. In that situation, the analytical model predicts in a satisfactory way the tru e area of contact vs. the compressive force. In the second part of the paper, the model is extended to describe the time dependence of adhes ion. Predictions of the evolution of the physical area of contact vs. time are demonstrated, in cases of both conformal and non-conformal co ntact conditions. The relevance of the model is further discussed.