Mechanical behaviour and fatigue lifetime of natural rubber reinforced by two grades of precipitated silica

摘要

White reinforcement fillers such as precipitated silica particles are traditionally used in order to increase tear resistance and reduce internal heating of technical rubber components. In tyre industry, a new generation of silica called highly dispersible silica (HDS) has been reported to enhance low rolling resistance while maintaining or improving longevity or adherence. In this work, two precipitated silicas which essentially differ in surface specific area are considered. They have been incorporated into a natural rubber matrix. Two reinforced rubber materials have thus been elaborated, allowing analysing the mechanical behaviour and fatigue lifetime of both materials. To this end, cyclic tension/compression and torsion tests have been carried out on dog-bone shaped specimens. All tests have been pursued until crack initiation, corresponding to a visible millimetric crack on the outer surface of the specimens. Microscopic examinations are utilised in order to find out the crack growth mechanisms in both materials. In terms of mechanical behaviour, both materials of interest exhibit visco-hyperelasticity and stress softening effects. A stabilised hysteresis loop is defined in order to overcome the difficulty related to Mullins and longterm viscoelasticity effects. This allows simplifying finite element (FE) modelling that gives access to the local stress state inside the specimen. Then with the help of local parameters computed by FE analysis, the fatigue lifetime is characterised. The extension of the fatigue lifetime due to the mean/minimum stress effects is studied. The location of crack initiation, as well as the number of cycles to initiation, are predicted by using a post-processor with adequate local parameters.