Study On Pore Breakdown Characteristics Of Rock By High Voltage Pulse Discharge

High voltage electric pulse rock breaking technology is a new type of non-contact rock breaking technology with extraordinary efficiency,environmental protection and energy saving.The core is that high voltage pulse energy supply forms a plasma channel inside the rock to break the rock.There is still a certain gap in the study of the breakdown process of high voltage pulse in the rock pore.By means of physical modeling,theoretical analysis and finite element simulation,we studied the characteristics of high pressure pulse breaking rock pores,and set high pressure pulse rock breaking experiment to analyze the relationship between pore and rock electrical damage.Our findings are as follows.Firstly,we study the particle motion and basic chemical reaction of plasma,and analyze the high pressure pulse rock breaking process and the role of pores in the crushing process.We establish the physical model of surrounding rock-pore and compute the electric power of the drift diffusion motion of plasma particles.We calculate the collision power of the electrochemical reaction and set up the boundary conditions.We obtain the thermal power of the plasma reaction through energy conservation.We set up the thin wall of the surrounding rock for Simplified calculation and gain the thermal expansion force by using the thermal stress calculation formula.Then,we use COMSOL Multiphysics to explore the electrical breakdown processes and thermal rupture processes in the pore breakdown of high voltage pulse simulation.We simulate the process of high voltage electrical pulse acting on rock pores.We achieve simulation convergence through plasma,thermal expansion,mesh and solver setup.It is found that the electron density increases slowly and the heat of the reaction changes abruptly during the reaction process.The thermal expansion stress can make the surrounding rock crack after the 13 k V high voltage pulse breaks down the pores.Finally,we set up a high pressure pulse rock breaking experiment system,and carried out 1k J high pressure pulse experiment with energy input on concrete blocks with different porosity of 7%,5% and 1%.It is concluded that the damage degree of rock increases with the increase of porosity,but the growth rate of the damage degree of rock sample decreases when the porosity increases to a certain extent.At the same time,it is found that the internal damage of rocks containing pores is anisotropic after high pressure pulse test.