Cyclic Behaviors of Granular Materials under Generalized Stress Condition Using DEM

Most behaviors of granular materials have been studied under the limit conditions of stress paths such as cyclic triaxial compression and extension tests. Furthermore, the macrobehavior and micromechanical response of granular materials under more comprehensive cyclic loading tests in the generalized stress condition are not well understood. The objectives of this paper are to ensure the ability of the Discrete Element Method (DEM), to simulate the macrobehavior of granular materials under various cyclic stress paths of the generalized stress condition, and to explore the micromechanical response. To this end, four different cyclic stress paths under generalized stress simulations, following the stress-controlled method on a sample of spheres, were conducted. To check the validity of DEM results, the experimental results of the real sand under cyclic stress programs were used. The macrobehaviors, indicated by the stress–strain–dilation relationship and the directions of principal strain increment vectors, are described. A qualitative comparison of the stress–strain–dilation between the DEM and experimental results under triaxial cyclic loading shows a similarity tendency. Furthermore, micromechanical responses, which are indicated by coordination number and sliding contact fraction, are used to explain the macrobehavior in cyclic loading. Additionally, the macro–micro relationship is explained using the relationship between the stress ratio and the fabric structures of all contacts, and of only the strong contacts. The result shows that the unique macro–micro relationship does not depend on the generalized cyclic stress path or the number of cycles.