The asymmetry of stress in granular media

Here, we show that the average stress in granular media, which is de®ned from virtual work, may be asymmetric in the absence of contact moments. We specify the circumstances and amplitude of stress asymmetry, and calculate the corresponding couple stress and ®rst stress moment. We also show that the average stress is always symmetric, when it is alternately de®ned by using statics and no contact moment. The stress asymmetry, which results from external moments, has an amplitude that decreases with the volume size. The present analysis applies to two- and threedimensional particles of arbitrary shapes. The asymmetric stress, couple stress and ®rst stress moment are analytically calculated in a particular example with cylindrical and spherical particles. Ó 2000 Elsevier Science Ltd. All rights reserved. Keywords: Granular mechanics; Couple stress; Stress asymmetry; Discrete particles