This paper presents a pilot numerical study into the rolling compression induced disintegration modes of a coal prism within a mill of vertical roller type. To simulate the breakage process characterized by large deformation and the transition from continuum to discontinuum, the coal prism was modeled with the smoothed particle hydrodynamics (SPH) method, and the mill structure was modeled by the finite element method (FEM) method. The interaction between the coal specimen and the roller was considered by introducing a master-slave contact boundary. The main aims of this study are to investigate the effects of specimen size and slenderness ratio on the disintegration modes of coal prisms. It was found through parametric analyses that the disintegration modes of the coal prisms would be significantly affected by the variations in specimen geometry.
The rolling-compression-induced crush response of brittle materials, such as ice and various types of rock and ore materials, is a common issue in a wide range of engineering practices. For instance, in a vertical roller mill, coal blocks would be arranged on a horizontal table and crushed into finer particles under the self-gravity action of the rotating steel roller component. A correct prediction of the breakage process of coal blocks and the interaction force along the interface during the milling process is of great significance for grind mill design and for strength analysis of the machine components.
Coal-like geomaterials are commonly characterized by internal imperfections and micro-cracks. Hence the crush failure process of a single coal block would firstly be influenced by the inelastic or permanent deformation of the block as a whole, that is, the block's volume will be largely conserved at this stage. Secondly, when the material block is disintegrated into several smaller parts, the space between them may become smaller by the continuing compression, and the complex interactions between these smaller parts also contribute to the inelasticity involved in the crush process.
Intensive experimental studies have been undertaken by many researchers for investigation into the crush failure of a single block under uniaxial compression, and a variety of materials have been tested, such as glass, rock, concrete, and plaster materials. On the other hand, for the crush response of blocks assembly, most of previous studies were focused on the response of a large number of specimens arranged into a pack, and a more or less lateral confinement was mostly incorporated. The working condition in a roller mill, that is, loosely arranged coal blocks at the initial stage, has not been included in previous research reports.