A micromechanical study on the stress rotation in granular materials due to fabric evolution

• Coaxiality exists in assemblies with circular or randomly elongated particles.
• Inherent anisotropy causes non-coaxiality between stress and strain directions.
• Contact vector direction plays a role in the prediction of principal stress axis.
• The complete form of SFF predicts well non-coaxiality behavior of assemblies.

In the present study, the non-coaxiality between the axes of principal stress and strain rate tensors is investigated from micromechanical point of view. Based on the so called stress–force–fabric (SFF) relationship, which describes the macro–micro relation, an expression is derived for the principal direction of stress tensor in terms of micromechanical parameters of the fabric. In general, the rotation of principal stress axis and accordingly, the non-coaxiality angle, are influenced by both the anisotropy coefficients and directions of anisotropy of the fabric characteristics. The derived macro–micro relationship was evaluated by performing DEM simulations of 2D specimens of aggregates. It was shown that the principal directions of anisotropy parameters are almost coincident for the assemblies containing circular particles or elongated angular particles with random distribution. In such case, the principal direction of stress tensor can be regarded as the average principal direction of anisotropy. However, when the aggregate with elongated particles has inherently-anisotropic fabric, a correct estimation of the stress angle rotation requires considering all the anisotropy parameters including both anisotropy coefficients and directions.

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