Study On The Effects Of Different Temperatures And Pore Structure On Mechanical Characteristics Of Lump Coal

China has a large amount of coal to crush for utilization every year.Coal breakage processes have high energy consumption and low efficiency.Hench,study on this process is of great significace for the clean and efficient use of coal.In this thesis,three Chinese typical coal types,Shenmu Coal(SM),Hongshaquan coal(HSQ)and Wucaiwan coal(WCW),were selected to study the mechanical properties under 90?,120?,150?and180?.From the fractal level,the relationship between meso-structural characteristics of coal surface and mechanical behaviors was established,and the three-dimensonal models of coal were reconstructed by finite element analysis to simulate the mechanical processes.The main contents and results were as follows.Firstly,the basic physical parameters and pore structures of three coal types were measured.The results show that the Hardgrove grindability index(HGI),porosity,pore size,apparent density and percolation fractal dimension have a good consistency,which is SM<HSQ<WCW.SM is the most difficult to grind,and WCW has the most complicated pore structure.Based on the fractal theory,the fractal dimension D was calculated by digital image processing and programming softwares.Comparing the theoretical and calculated values of typical fractals,the results show that the calculation is great accurate and reliable.Then,the uniaxial compression tests of three coal types under different temperatures were carried out on a self-designed bench.The results show that the compressive strength?_m(MPa)and elastic modulus E(MPa)have overall downward trends.Due to the thermal expansion of coal matrix and water inside closed pores,the mechanical strength of SM increases slightly in the range of 120?and 180?.By means of fractal theory,the meso-structure of coal surface can characterize the mechanical properties.Two dimensionless parameters of the relative fractal dimension D_r and the relative stress?_r were introduced to quantitatively characterize the meso-structural and mechanical properties.The results show that when the?_r is higher than 0.75,the relative fractal dimension grows rapidly,and the two dimensionless parameters can be described as a temperature-denpendent exponential function.Finally,through finite element analysis,three-dimensional models of solid,horizontal cracks and vertical cracks were constructed to study the effects of cracks on the mechanical behaviors under uniaxial compression.The results show that the compaction phenomenon of horizontal cracks make the mechanical curve fluctuate.Based on the mercury intrusion test and random number function,the three-dimensional porous structure of lump coal was reconstructed.The simulated results and test results have a good consistency in the overall trend.