On distortion of tensor and yield criteria of granular materials

The distortion of tensor defined by use of normals on the tensor ellipsoid and the mean distortion are introduced. It is explained that the distortion represents the unit shear strain for the finite strain tensor, and the shear-normal stress ratio for the stress tensor. The spatial mobilized plane which plays a very important role in the mechanics of granular materials is regarded as a plane on which the distortion of stress tensor coincides with its mean distortion, and the yield criteria of granular materials are considered applying the concept of the distortion of stress tensor.