ABSTRACT
The finite element method (FEM) simulation is a strong and important tool to design the industrial rubber products because in many cases, they are subjected to complex deformations in use. The FEM analysis requires the constitutive equations which accurately describe the stress-strain behaviors under all types of deformation. Many types of phenomenological constitutive equation for rubbers have been proposed (For a review, Beda 2005). The determination of the model parameters or the assessment of the models has often been made using the uniaxial deformation (stretching and/or compression) data due to the experimental simplicity. The analysis relying on only uniaxial deformation often leads to incorrect results because the uniaxial deformation is only a particular one among all accessible deformations of rubbers (Treloar 1949, Urayama 2006). Evidently, the stress-strain data under various deformations provide unambiguous basis to establish the reliable constitutive equations. In principle, general biaxial strains with varying independently the principal strains in the two orthogonal directions cover the whole range of accessible deformations of incompressible rubbers. We demonstrated that the stressstrain data of the silicone rubbers under general biaxial deformations provided a definite basis to
deduce a phenomenological form of strain energy density function (W ) as well as to assess various molecular theories of rubber elasticity (Kawamura et al. 2001, Urayama et al. 2001).
