Experimental and computational aspects of cavitation in natural rubber

Abstract

General constitutive equations for hyperelastic materials are based on the first law of thermodynamics whereby the total strain energy function is expressed either in terms of strain invariants or principal stretches. For most applications the strain energy functional does not need to include dilatational components. However, the pressure–volume relationship for nearly incompressible materials must be explicitly accounted for when rubber components are highly constrained. Thus, the hyperplastic response needs to be expressed in terms of dilatational and deviatoric components. Experimental evidence has been reviewed to show that rubber is subjected to a loss of stiffness attributed to cavitation damage when subjected to a hydrostatic tensile stress state. The critical pressure is identified for which microscopic material imperfections will tear open to form internal bubbles and cracks.

Cavitation damage in rubber is associated with a significant reduction in the bulk modulus. Thus, a variable bulk modulus can best be used to describe the behaviour of rubber when cavitation damage occurs. The introduction of a cavitation damage modulus is suggested as a simple approach to represent realistically the mechanics of cavitation in rubber solids.