Compression of unbonded rubber layers taking into account bulk compressibility and contact slip at the supports

The behavior of rubber layers under pure compression has been investigated to considerable extent in the literature. The most widely used approach is the so-called pressure solution, which is based on several assumptions, most notably that the stress state is dominated by the hydrostatic pressure. Other approaches have also been considered, but for nearly incompressible material and thin layers their predictions are very similar to those of the pressure solution. Nearly all past studies on the subject have focused on rubber layers that are bonded to either rigid or flexible supports (or reinforcement). Unreinforced (i.e., single layer) rubber pads are often installed as unbonded, i.e., without steel end plates connecting them to their top and bottom supports. In an unbonded application, rubber pads rely solely on friction to develop shear resistance along the contact interfaces. This shear resistance is necessary to provide the pad with an adequately large vertical stiffness. The effect of the frictional restraint along the top and bottom contact surfaces and the influence of partial slip have received very little attention in the literature. In this paper, we present a theoretical analysis for the behavior of an unbonded rubber layer, including the effects of the elastomer’s bulk compressibility and the contact slip at the supports. Results of a finite element analysis are also presented and shown to be in good agreement with the results of the theoretical analysis.