Fracture mechanics and the adherence of viscoelastic bodies

The strain energy release rate G and its derivative delta G/ delta A are used to provide a general picture of the adherence of viscoelastic bodies. Two bodies in contact on an area A are in equilibrium if G=w, where w is the thermodynamic (or Dupre's) work of adhesion. The quasistatic force of adherence is the load corresponding to delta G/ delta A=0. When G>w, the separation of the two bodies starts, and can be seen as the propagation of a crack in mode I. Three geometries are investigated: adherence of spheres, adherence of punches, and peeling. The variation of energies with the area of contact is given, and the kinetics of crack propagation are studied. The theory is supported by experiments on the adherence of polyurethane to glass.