Modelling the Deformation of Sand during Cyclic Rotation of Principal Stress Directions

The paper presents an elastoplastic constitutive model for the deformation of sand during cyclic rotation of principal stress directions. The model employs a plastic potential theory that allows for the dependency of flow on the stress increment direction and a stress-dilatancy relation incorporating the effects of noncoaxiality. The continuous plastic deformation of sand during principal stress rotation at constant shear stress level is allowed for in the model by using a small elastic area in the stress space. The effects of cyclic stress history is modelled by using discrete surfaces of equal hardening modulus which are allowed to move with the stress point during loading. Additionally, the plastic hardening modulus is allowed to stiffen during cyclic loading depending on the amount of accumulated plastic normalized work. The model is used to simulate the deformations in the hollow cylindrical specimen subjected to several cycles of principal stress rotations. The model is shown to be capable of satisfactorily predicting the response of sand during cycles of principal stress rotations