Viscoplasticity of elastomeric materials: experimental facts and constitutive modelling

A characteristic of filled elastomers is their ability to undergo very larg e deformations without damaging their internal structure. The material beha viour is mainly elastic, however, elastomers show hysteresis effects leadin g to damping properties, which are quite important as regards their applica tions in various fields of mechanical engineering. A series of experiments (tension, torsion and combinations of both) was car ried out on cylindrical bars made of a carbon-black filled rubber mixture. In addition to a pronounced nonlinear rate-dependence, relaxation and visco sity properties are observed as being influenced by the process histories. The behaviour of elastomeric materials is modelled on the basis of a free e nergy function and evolution equations for additional internal variables. I ncorporating or disregarding the very small rate-independent hysteresis, th e constitutive modelling may be classified under viscoplasticity or viscoel asticity. The constitutive equations are formulated for isothermal processe s in a thermodynamically consistent manner. Particular attention is focused on nonlinear rate-dependence as well as on process-dependent relaxation pr operties. Numerical simulations on the basis of identified material paramet ers show that the proposed constitutive model is able to represent the main elastic and inelastic phenomena.