Coupled distortional-dilatational failure mode concept for silicone adhesives

Abstract

Nearly incompressible rubber-like materials, such as silicone adhesives, exhibit two failure modes: dilatational and distortional failure. The former corresponds to the formation and growth of cavities owing to triaxial deformation. The latter corresponds to fracture due to excessive isochoric deformation, i.e. deformation at constant volume. Both failure modes are typically assessed individually and corresponding failure criteria are often formulated in terms of stresses. However, stress-based descriptions of failure depend explicitly on the choice of constitutive law and the experimental measurement of critical stresses is challenging or even impossible. Therefore, recent studies proposed strain and stretch-based criteria for distortional failure of nearly incompressible hyperelastic materials, that can be obtained directly from optical measurements using digital image correlation.The present work exploits stretch-based descriptions of both failure modes to provide a unified coupled dilatational-distortional failure criterion which describes the complete failure surface of nearly incompressible silicone adhesives or rubber-like materials in general. For this purpose, we propose a stretch-based cavitation criterion which depends on a single parameter. Distortional failure is described by the Podgórski-criterion formulated in principal stretch space. The coupled dilatational-distortional failure criterion is validated using uniaxial tension, bulge and pancake tests of the nearly incompressible hyperelastic transparent structural silicone sealant DOWSIL™ TSSA. It is shown that the proposed failure criterion captures both the onset of cavitation and ultimate distortional failure in very good agreement with all experiments.