Quantitative Description Of Rock And Mineral Particle Shape And Its Application To Microwave Irradiation Evaluation

When the hard rock section is excavated by mechanical method in underground engineering,the tool and equipment wear seriously and excavation efficiency is significantly reduced.Microwave-assisted rock breaking technology can greatly improve the excavation speed and efficiency to a certain extent.There are many factors affecting the result of microwave-assisted rock breaking,such as rock mineral particle morphology,content,particle size,characteristics and microwave irradiation mode.According to the current understanding,the mineral shape,as one of the important characteristics of rock,has an important influence on the microwave-assisted rock breaking effect.In this paper,the influence law and result of rock and mineral particle shape on microwave-assisted rock breaking are studied,and the main shape characteristics and quantitative description methods of rock and mineral particles are analyzed.The influence of shape characteristics of mineral particles on the softening effect of microwave irradiation is studied by using the finite element analysis software COMSOL,which can simulate the electromagnetic,thermal-mechanical coupling in process of microwave irradiation.The comprehensive parameter of mineral particle shape is created to quantitatively describe the shape,and the application of prediction and evaluation of the weakening effect of microwave irradiation on rock is carried out.The main research contents and results are:(1)The shape model of mineral particles was established,and the shape characteristics and quantitative description methods of common rock forming mineral particles were analyzed.The results show that the shape characteristics of mineral particles can be described from three aspects:overall shape flattness,contour texture roughness and sharpness.Different particle shape quantization parameters have different emphases and advantages and disadvantages when describing mineral particle shape.Flattness,roundness and sharpness have better shape description effect and can be applied to numerical simulation test and analysis.(2)Using the finite element simulation software COMSOL,the shape analysis model of rock mineral particles with flattness,roundness and sharpness was established,and the influence of the shape characteristics of rock mineral particles on microwave irradiation effect was studied.The results show that the lower the flattness,roundness and sharp Angle shape parameters of the specimen with the same content are,the lower the central maximum temperature of the specimen will be,and the larger the maximum temperature gradient of the specimen will be under the same irradiation time of 1.5kW microwave irradiation.The larger the first principal stress is,the more uneven the distribution is.The earlier the initiation time of the plastic zone,the faster the plastic zone develops and the larger the area.(3)Based on the global shape flattness parameters and local curvature characteristics of particles,the comprehensive parameter SF(dimension-less),SF?(0,1),is proposed to quantitatively describe the shape characteristics of rock and mineral particles.It includes the basic idea of parameter proposed,the establishment process and calculation method,the visual comparison of particle morphology of shape synthesis parameters,and the evaluation of the development area of plastic zone of rock irradiated by microwave and the analysis of its advantages.The results show that the value of shape synthesis parameter changes from small to large,which can describe the mineral shape characteristics from the flat shape with rough texture gradually to the round shape with smooth contour texture.The smaller the shape synthesis parameter,the larger the plastic zone area.(4)According to the proposed shape synthesis parameters,the application research of mineral shape synthesis parameters in the evaluation of the softening effect of microwave irradiation rock was carried out.The results show that:When mineral particle shape control for single variable shape comprehensive parameter to the weakening effect of microwave irradiation in different specimen evaluation application present good map,mineral particle shape comprehensive parameter value forecasting evaluation to the effect of microwave irradiation is consistent with the numerical simulation results,the comprehensive shape parameter value is smaller,the lower the temperature of the specimens,The larger the temperature gradient value and the first principal stress value,the larger the plastic zone development area,that is,the smaller the shape comprehensive parameters of the single particle absorbing mineral particle,the better the microwave irradiation effect of the rock specimen.