Fractal Study On The Physical Structure Of Coal Particles And Its Relationship With Mesoscopic Mechanical Characteristics

Enhancing the energy utilization of coal breaking is an important subject in coal utilization technologies. This thesis studies the evolution of the crashing process from a new perspective, meso mechanics based on fractal theory. Taking four typical coals, Yangquan, Shenmu, Hongshanquan and Wucaiwan as research objects, combined with uniaxial compression mechanics, fractal theory and image processing technology are used to perform research on mechanical properties and structural evolution of coal particles. Meanwhile, theoretical and experimental supports are provided for mechanical 3D- model reconstruction of coals. This thesis mainly includes the following parts:Firstly, the application range and method of fractal theory are discussed. In this thesis, the meso-structure images of coal surface are obtained from digital microscope.ImageJ is used for images processing to extract the information about meso structure o f coal surface effectively. The fractal dimension numbers on the meso structure of coal surface are calculated with MATLAB program. A method is established to explore the meso structure of coal suface quantitatively according to fractal theory and image processing technology.Secondly, the mechanical properties are influenced by basic physical properties and meso porous structures of coal particles. Different methods are applied to measure the properties of the four coals. Study shows Yangquan is anthracite, Shenmu, Hongshanquan and Wucaiwan is bitumite of different metamorphism by proximate analysis and ultimate analysis;Grindability test shows Yangquan, Shenmu, Hongshanquan and Wucaiwan coal's HGI increased;Mercury porosimetry and nitrogen adsorption are used to measure hole pattern?porosity?pore size distribution? specific surface area, and calculate fractal dimension of pore structure;Calculate fractal dimension of surface meso structure of coal digital image obtained by stereo microscope. Above results provide experimental parameters for building coal mechanical model.Thirdly, mechanical experiments are performed on a mechanical test bed of uniaxial load. Our research indicates that uniaxial compression breaking of coals has four stages, compaction, linear elasticity, yielding and plastic failure. Main damage forms are splitting failure of main crack along the longitudinal direction. Most of coals obtain anisotropy on stress intensity and elastic modulus. Elastic modulus obtained from uniaxial compression test of coals is positively correlated with compressive strength.At last, fractal dimension numbers are used to indicate the meso-structural change of coal surface during the loading process dynamically. O ur study shows that with the increase of stress, fractal dimension numbers increase in slower rates at first and then in larger speeds. The relationship between fractal dimension number of meso structure and stress intensity is D=A*e^(f(?))+B for most of coals, where A and B are constant, f(?), linear function.