EXPANSION OF A CAVITY IN A RUBBER BLOCK UNDER UNEQUAL STRESSES

Elastic expansion of a small spherical void in the interior of a rubber block has been investigated by finite element analysis (FEA). The block was subjected to a far-field tensile or compressive stress while an internal pressure was applied to the cavity. The rubber was assumed to be virtually incompressible in volume and neo-Hookean in elastic behavior. Critical stress states were determined at which the void would become indefinitely large - a form of elastic instability. An applied tensile stress was found to lower the critical inflation pressure for instability, in agreement with experimental observations [1] whereas a compressive stress increased it. The critical mean stress was lowest for an isotropic stress system (when the applied tension was zero). It was higher when either compressive or tensile stresses were applied, i.e. under non-isotropic stresses, in agreement with the analysis of Hou and Abeyaratne [2]. However, the present results show a considerably smaller effect of tensile stress than predicted by Hou and Abeyaratne.