Jinhua Zhang

An algorithm for the grain-level modelling of a dry sand particulate system

This paper is composed of two parts: the generation of the sand particulate system and insights into the grain-level response under static and dynamic loadings. First, the algorithms for the generation of sand particles are presented, considering the randomness in their shape and distribution. Improvements to the robustness of the algorithms are obtained using controlling parameters. Second, we employ the take-and-place algorithm, placing sand grains into the specimen and checking how they overlap to form the initial model. In order to improve the porosity of the specimen, we develop the compaction algorithm: self-compaction by gravity and artificial compaction by mechanical vibration and pressure. The steps for the generation of a finite element grid are also introduced. Third, the grain-level configurations of the dry sand particulate system (aspects such as porosity, friction and contact) are taken into account in modelling. Results show that the grain-level responses of grains, i.e. deformation, fracture and damage of sand grains, impose significant effects on the mechanical behavior of dry sand under static and dynamic loadings.

3D Numerical Investigation of Cement Mortar with Microscopic Defects at High Strain Rates

AbstractThis paper develops a three-dimensional (3D) microscopic model to investigate the mechanical response of cement mortar with random defects at high strain rates. Ellipsoids with randomness in size, shape, and spatial distribution are used to simulate the defects in mortar matrix. First, we propose the steps to generate the ellipsoid. Second, a “take and place” algorithm is employed to generate a model of cement mortar composed of defects. The mapping algorithm is used to generate a finite-element grid. In finite-element modeling, the material model is used in an advanced general-purpose multiphysics simulation software package to simulate the nonlinear behavior of mortar matrix with strain rate effects. Numerical simulations of the specimen under static loadings agree well with test observations, which reveal that the proposed 3D microscopic model and finite-element analytical approach can give reliable predictions. Finally, numerical studies are conducted, focusing on the effect of the defects on ...

Mesoscopic investigation of layered graded metallic foams under dynamic compaction

This article is aimed to reveal the dynamic response of layered graded metallic foam under impact loading using a three-dimensional mesoscopic model. First, a mesoscopic model for closed-cell metallic foam is proposed based on the X-ray computed tomography images. Second, a numerical analysis approach is presented and validated with test data. Third, it studies the dynamic behavior of the layered graded metallic foam under impact loading numerically. The metallic foam specimen is composed layer by layer. The porosity, which is a fraction of the voids volume over the total volume, is different with each other for the layers. Simulations are conducted to the specimen with increasing and decreasing porosity arrangement. Results show that the layer arrangement is critical to the dynamic properties. The mesoscopic deformation of cell walls and the energy absorption capability are also affected significantly. This article gives insights into the mechanical properties and mesoscopic deformation of layered graded metallic foam.