Compressibility induced by damage in carbon black reinforced natural rubber

Natural rubber is commonly considered as an incompressible material. This study shows how carbon black reinforced natural rubber (NR-CB), when subjected to various mechanical loading conditions (uniaxial, hydrostatic, monotonic, cyclic), is affected by volume change. The mechanisms of volume change seem to be related to a competition between damage evolution, chain orientation and viscoelasticity. At a microscopic scale, in-situ Scanning Electron Microscopy (SEM) examinations and image analysis allow to record damage evolution as a function of elongation. It comes out that the volume change and damage evolution behave in a proportional manner. Based on the experimental results, we adopted a nearly-compressible approach, where the strain energy is assumed to be the sum of damageable spherical and deviatoric parts. Damage was accounted differently in spherical and deviatoric parts. Good agreement was obtained between experimental results and model predictions.