ABSTRACT

The form of Strain Energy Function (SEF) depends on symmetry, thermodynamic, energetic and entropic considerations. For example, in the case of rubber-like materials, due to the negligible compressibility of material under conventional pressures, incompressibility assumption is often used (I3 1= ). Therefore, we can conclude:

W W= ( )I I1 2, (3)

The choice of the appropriate SEF depends on its application, corresponding variables and available data for Material Parameters Identification (MPI). The validity of possible models should be studied and the simplest is selected with high accuracy and low number of material parameters (Lemaitre 2001). An efficient hyperelastic model can be defined by four main qualities (Chagnon et al. 2004):

• It should have the capability of reproducing the whole ‘S’ shaped behavior of rubber-like materials.