Hyperelastic behaviour identification by a forward problem resolution: Application to a tear test of a silicone-rubber

The mechanical behaviour of synthetic rubbers shows very high deformability, compressibility, time-dependent effect and strain softening. The present study is devoted to the analysis of local mechanical behaviour of silica-filled silicone rubber. New testing and identification are proposed in this paper by using standardised tear test, kinematic field measurements and a numerical inverse problem resolution to investigate localisation strain phenomena. The experimental procedure described hereafter, is based on strain field measurements using digital image processing. In-plane kinematic measurements by the digital image correlation are suitable to analyse non-homogeneous mechanical tests performed especially on thin sheets: indeed, rubber-like materials are characterised by a very high deformability and a non-linear behaviour leading to important gradients of deformation. The identification procedure is conducted in two steps. First, parameters of the viscosity and stress softening (Mullins effect) are evaluated analytically by using axial and biaxial tensile tests. Then, hyperelastic parameters are identified by an inverse resolution based on standardised tear tests. The mechanical model is implemented into the finite element code Zebulon (Transvalor/ENSMP). The numerical model is built up by using informations on geometry and boundary conditions extracted from image sequence that were acquired during the test. Usage of different functions evaluating the distance between computed and experimental quantities (cost functions) in a minimisation process is discussed.