Research On Charge Sensor Calibration Of Rock Mass And Three Point Bending Experiment Of Granite

Monitoring of charge induction signal in rock mass destruction process is an important method to prevent dynamic disasters of mine.The charge induction signal has the advantages of non-contact and strong anti-jamming capability.But there is no special charge induction signal risk indicators to do specific guidance on engineering application.The study on basic theory of electromechanical coupling,charge sensor working principle and calibration,effect of non-rupture factors on charge signal and three point bending test of granite was conducted in this paper,and the results were as follows.(1)The charge induction signals are released by rock fracturing,which is realized through the combined action of bound state charge distortion becoming free electronic then escaping and piezoelectric effect and triboelectrification of rock mass during loading process.The electric field produced by rock fracture releasing charge induction signal belongs to vortex elelctic field.And it can be simplified to get electric dipole isotropic model.(2)The two calibration methods of contact and non-contact calibration were used to do charge sensor calibration,the results showed that: the result of non-contact calibration is larger.The contact calibration test showed that the signals obtained through charge sensor monitoring are affected by charge polarity,and the calibration result is 45mV/pC;The non-contact calibration test showed that,the calibration result and sensor sensitivity are 80mV/pC and 9 respectively,when radius of charge sensitive element is 10 mm,and the distance between sensitive element and object to be tested is 5mm.(3)After 8.5s of charge induction signals natural discharge,which are released during the process of coal and rock fracture,the amplitude reduces by 10%.The charge induction signal monitoring can monitor charge induction signals released by coal and rock fracture timely and accurately.The charge induction signals are greatly influenced by the distance.The one-dimensional formula and two-dimensional mathematical formula are established,and the experimental verification showed that the formulas can reflect the influence law of distance on charge induction signals.The study on charged particle velocity showed that,the bigger the charged particle velocity,the greater the fluctuations of charge induction signal characteristic value and the wider the signal frequency band will be.(4)The bigger the loading speed,the easier the rock sample fracture will be,the smaller the displacement and peak load will be.The bigger the span,the easier the rock sample will fracture,and the smaller the peak load will be.The bigger the loading speed,the lower the peak,root mean square and standard deviation of charge induction signals released by granite compression fracture will be.The bigger the span,the fewer the pulse count and cumulative charge of charge induction signal will be.The charge induction signals produced by granite compression fracture are richer that released by granite tensile fracture.The cumulative charge of charge induction signals released by granite fracture in pressure and tensile surface have an opposite charge.The proposition of charge sensor calibration method and setting of charge induction signal threshold provide basis for prevention and control of mine dynamic disasters.