Abstract
The concept of effective strain is proposed as a reciprocal concept of the effective stress. The effective strain is defined as strain minus volumetric strain due to dilatancy. Though the overall volume of granular material remains the same during shearing involving no volumetric strain increment, the volume of void can change due to the rearrangement of the particles. On this reflection, it is postulated that the relative displacements of the centers of the particles which are in contact in granular materials are, in the average, consistent with the effective strain. This leads to the concept of the effective strain energy which is defined with respect to the effective strain. Though a plasticity model with micromechanical background (Iai, 1993b) is not exactly expressed in the associated form, its flow rule becomes associated if it is defined in the effective strain space. Drucker's stability postulates defined with respect to the effective strain energy are also seen to be satisfied by the present model. Thus, introduction of the concept of the effective strain may be one of the efficient approaches to solve the controversy over the non-associated flow rule and Drucker's postulates in the constitutive modeling of granular materials.
