Parametric Study of Hypoplasticity Constitutive Model for Granular Media via the Discrete Element Method
Date of Award
Master of Science (MS)
Granular media, as a general definition, includes a large class of materials, such as cereal grains; pharmaceutical tablets and capsules; geomaterials, such as sand; and the masses of rock and ice in planetary rings. Alternatively, a granular material could consist of highly fractured rock masses regarded as cracked elastic solids. In all cases, a very important property of granular media is their ability to yield, that is, exhibit irreversible deformation properties. Because the granular elastic modulus ‘G’ is the key relevant stress parameter, there is an interesting and nagging question as to the microscopic origins of the stress scales assumed in various empiricisms associated with critical-state soil mechanics and Hypoplasticity. This question may reflect a philosophical divide, separating those concerned with the relation of constitutive equations to micromechanics, from those whose primary concern is correlation of data from laboratory and field tests.The goal of this research is to first understand how hypoplastic constitutive equation works to account for the granular material behavior. From the original Hypoplastic constitutive equation which was introduced by Kolymbas, Lade-Duncan, Mohr-Coulomb and Matsuoka-Nakai yield surfaces (which are regarded as the significant approach for yield prediction in elastoplasticity theory) are generated. Then, with the Discrete Element Method (DEM) true-triaxial test results, the parametric study is processed by the developed inverse hypoplastic constitutive equation. The results show the concept of inverting the hypoplastic constitutive model is capable of generating the actual and effective non-dimensional material parameters. Due to the input of the improved stress and strain obtained from the true-triaxial test, the improved method is shown to be improved from original experimental data. Also, the Hypoplastic method performs as effective as the other previous method such as elastoplastic.