Infrared Radiation Response Mechanism Of Fracture Sandstone During Loading

The damage and fracture of rock is the fundamental cause of coal mine dynamic disasters such as coal and gas outburst,rock burst and mine water inrush.It is also one of the basic and common scientific problems in the field of rock engineering.Accurate and effective monitoring of rock damage and fracture process can provide reliable precursor information for coal mine dynamic disaster early warning.It is an important basis for monitoring and early warning of surrounding rock fracture and water seepage(water inrush)in mining face.The change of infrared radiation will accompany the process of rock loading and fracture.However,most of the current studies focus on the infrared radiation variation characteristics of the loaded rock surface,but do not establish a quantitative relationship between the infrared radiation information of the rock surface and its internal damage and fracture characteristics.This defect restricts the application of infrared radiation in the field of mine disaster monitoring and early warning.Based on this,the biaxial experiments of sandstone under different lateral stresses are carried out in this paper.Using the self-designed multi parameter monitoring system of loaded rock,the characteristics of acoustic emission and surface infrared radiation of loaded sandstone are clarified,and the internal relationship between infrared radiation and internal damage and fracture of rock is established.The three-dimensional plastic damage constitutive model of sandstone based on infrared radiation information and the "seepage-temperature" evolution model of sandstone under hydraulic coupling are constructed.The conclusions of this paper are mainly reflected in the following:(1)The characteristics of infrared radiation noise curve during biaxial loading of sandstone are analyzed,and a subregional denoising method of infrared radiation temperature curve is proposed,that is,the experimental sample and reference sample are divided into multiple regions,the subregions of each experimental sample are subtracted from all subregions of the reference sample,and the correlation coefficient of polynomial fitting function is determined as the evaluation index of subregional denoising.On this basis,the Gaussian kernel function is used as the influence function to evaluate the influence of a temperature point on the surrounding temperature area,and the infrared radiation energy is introduced as the infrared index to determine the threshold of the Gaussian kernel function,so as to judge whether the temperature point is noise.This method can quickly detect the infrared radiation outliers and effectively solve the problem of fluctuation and drift of the infrared radiation temperature curve.Combined with the sub region denoising method,a new average infrared radiation temperature denoising model of "sub region-Gaussian kernel function" is constructed,which not only innovates the infrared radiation denoising method,but also solves the problem of infrared radiation temperature distortion of biaxial loaded sandstone.(2)Based on the infrared thermal image,the threshold of high temperature point in the infrared radiation temperature matrix is determined by the percentile method,the amplitude of high temperature point scale factor is defined,the double standard deviation is used as the critical line of high temperature point scale amplitude mutation,and a new index of infrared radiation with cumulative high temperature point scale factor amplitude is proposed.Combined with the stress,cumulative ring count and the average infrared radiation temperature after effective denoising,a comprehensive evaluation model of acoustic and thermal in the process of sandstone loading and fracture is constructed based on the principal component analysis method,the probability function of failure in the process of sandstone loading and fracture is defined,and the quantitative analysis of the influence weight of each acoustic and thermal index on sandstone fracture is realized.On this basis,a new method to determine the failure precursor of sandstone based on the first derivative of acoustic thermal comprehensive evaluation model is proposed.This method overcomes the discrete analysis defect of acoustic emission and surface infrared radiation information of loaded sandstone.(3)Based on the transformation equation of plastic strain energy and deformation work,the equivalent plastic strain difference of sandstone is defined,and the friction heat effect of loaded sandstone is clarified;According to the Euclidean distance between the plastic zone and the crack tip,the temperature source density function of the crack plastic zone is characterized.Based on the Fourier law of heat conduction,the thermal effect of crack propagation is deduced and analyzed,and the mathematical model of infrared radiation response mechanism in the process of sandstone loading and fracture is established.Based on this model,the heat conduction range of sandstone under biaxial loading fracture is determined through the secondary development of finite element software.It is found that for the 50 * 50* 100 mm red sandstone used in this experiment,the maximum range of infrared radiation on the rock sample surface affected by the thermal effect of internal crack propagation is 0.981 cm,and the average infrared radiation temperature in the local high-temperature area of loaded sandstone is predicted.(4)It is found that the relationship between infrared radiation energy and effective stress is a near power function in the process of sandstone loading and fracture.The quantitative characterization method of infrared radiation for the first invariant of stress and the second invariant of deviatoric stress is established,and the amplitude of cumulative high temperature point scale factor is proposed to characterize the plastic volume strain of sandstone.Based on the effective stress and plastic strain,the plastic and damage models of sandstone are established respectively,and the three-dimensional constitutive model of plastic damage of sandstone under loading based on infrared radiation is constructed.The model has clear input parameters of physical significance,and the compaction stage of sandstone is considered.The stress prediction of sandstone during biaxial loading is realized through the secondary development of finite element software subroutine.(5)Based on the first law of thermodynamics and the expression of non-Darcy flow,the quantitative expressions of internal temperature and pore water pressure in the process of sandstone seepage are derived.Based on the double spring model,the stress of loaded sandstone is characterized by infrared radiation.Combined with the fracture seepage control equation and damage variable equation,the "seepage-temperature" evolution model of sandstone under hydraulic coupling based on infrared radiation is established.The seepage and temperature evolution curves are obtained through the secondary development of finite element software.On this basis,five artificial intelligence models with the internal temperature of sandstone as the output parameter are constructed.It is found that the significance of the prediction performance of random forest algorithm is more suitable for predicting the physical and mechanical parameters of rock under hydraulic coupling.There are 81 figures,5 tables and 206 references in this dissertation.