Contact mechanics and adhesion of viscoelastic spheres

The extension of the Johnson-Kendall-Roberts (JKR) theory of contact to viscoelastic materials is addressed. Because the energy flow to the material at the moving edge of contact is coupled to the local bonding or debonding process for viscoelastic materials, any such extension must account for the micromechanical process of bonding or failure if it is to avoid a paradoxical prediction. A crack bonding theory due to Schapery that uses a very simple model of the crack closing process is applied to the loading phase of a JKR type experiment. Numerical simulations show that this theory predicts results that are in reasonably good agreement with the experimental results of Falsafi et dr. There are, however, difficulties in applying this theory to the determination of the surface energy of a material, and an alternative method of characterizing adhesive properties is suggested.