Stress Fluctuations for Continuously Sheared Granular Materials

Experiments on continuously sheared granular materials (glass spheres) with diameters 1. 05mm show large fluctuations in the normal stress, (t). Experiments are carried out in an annular Couette geometry for rotation rates 0. 003< \. {}<1rad/s. Power spectra from (t), P (), show rate invariance in the fluctuations: \. {}P () is a function only of / \. {}, independent of \. {}. \. {}P () depends relatively weakly on d. The distributions of stresses _ are similar to recent predictions for static arrays, but the width of _ varies only weakly with d, suggesting stronger spatial correlation effects than expected from theory.