Experimental Stick-Slip Behaviour in Triaxial Test on Granular Matter

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This paper is concerned with the quasi-static rheology of packings of glass spheres of diameter d (d=0.2mm, 0.7mm or 3mm). Stick-slip behaviour is observed on small spheres, i.e d=0.2mm & 0.7mm; one observes also in this case a weakening of the rheology as the rate of deformation increases, and the larger the rate the larger the weakening; this generates macroscopic instabilities and stick-slip. Statistics of stick-slip events have been determined, which show that the larger the sample the more regular (i.e. "periodic") the sick-slip, the faster the strain rate the less periodic the events. One concludes that this stick-slip is generated at the macroscopic level and comes from the macroscopic rhelogical law. However when sample is small, local fluctuations perturb the macroscopic events and trigger them erratically. Pacs #: 5.40; 45.70; 62.20; 83.70.Fn