Aspects of cavitation damage in seismic bearings

Hyperelastic material models are derived from strain energy potentials expressed in terms of strain invariant or principal stretches. For a (nearly) incompressible material, the strain energy density depends on the first and second strain invariant; the third invariant describing a change in volume is equal to one. If the material is not highly confined it may be satisfactory to select an incompressible approach. However, for seismic bearings a highly confined situation does exist, and the compressibility must be included to obtain realistic results. Further, cavitation and associated stiffness reduction in bearings are shown based on experimental observations. In fact, it was noticed that a hydrostatic tensile stress in rubber causes internal rupture and a significant reduction in the bulk modulus. Thus, a hyperelastic formulation based on a variable bulk modulus does suggest a simple approach to realistically represent the mechanics of cavitation in rubbery solids.