Micromechanical analysis of non-coaxiality between stress and strain increment in granular materials

It is known that non-coaxiality between the directions of the principal stresses and the principal plastic strain increments in granular material is physically resulted from the material and mechanical anisotropy as well as their evolutions. A novel study was conducted to verify the contributions of the material and mechanical anisotropies to the magnitude of non-coaxiality during the rotation of the principal stress orientation. Micromechanical analysis indicates that the non-coaxial behavior can occur in a granular assembly with mostly non-sliding contacts acting. Moreover, the magnitude of non-coaxiality is a function of the stress level, the ratio of contact stiffness, the material and mechanical anisotropy as well as their evolutions. This has been confirmed by numerical simulation. The numerical results indicate that the non-sliding interparticle connectivity is one of the dominant sources of non-coaxiality. The interparticle sliding has been found to reduce the magnitude of the non-coaxiality.