ABSTRACT
We present an experimental study of the particle size and shape effect in the shear friction in a granular medium. Silicagel powders have been used, either spherical or ground and sieved. In both cases, the size distribution range has been limited to avoid segregation. These samples have been sheared in an annular shear tester. We observe first a decrease of the friction coefficient when using spherical particles instead of ground grains. The latter have the same coefficient of friction but do not have the same response with respect to the stick-slip shear instability. When interpreted using the Dieterich-Ruina model, we observe that the size of the grains changes the reduction in friction with the sliding velocity but not the critical sliding distance.
