FATIGUE LIFETIME OF A SILICA FILLED RUBBER. APPLICATION TO A SBR SHOE SOLE UNDER BENDING

摘要

This paper is devoted to the fatigue behaviour characterization of a silica filled styrene butadiene rubber (SBR). The first part concerns the experimental mechanical behaviour characterization of the material. Mechanical tests performed on both pure and filled gum highlight the large influence of the silica fillers on both damage and viscoelasticity of the compound. The identification of the visco-hyperelastic-damageinduced constitutive law parameters is based on uniaxial tests (tension and compression) under static, cyclic and relaxation loadings. The validation of the constitutive equation is performed by finite element analysis computations on axisymmetrically notched specimens, used for fatigue tests. Numerical results show a good agreement with experiments. Local strains and stresses are then calculated to evaluate the material fatigue lifetime. In the second part, the fatigue behavior is investigated. We aim to establish a fatigue crack initiation criterion, from the analysis of uniaxial and torsion tests performed on axisymmetrically notched specimens. Two parameters have an influence on the fatigue lifetime: the maximum of the largest principal strain, and the second strain-amplitude invariant. SEM fracture surface observations highlight the mechanisms of the crack initiation. Fracture takes place from points of weakness like silica filler heterogeneities or molding defects. A multiaxial crack initiation criterion is finally proposed for the prediction of the crack initiation number of cycles for a multiaxially loaded structure.