Mechanical Parameters Of Coal And Rock Samples Under Different Loading Rates Study On The Law Of Acoustic Emission

The mechanical properties of coal rock samples is a very important research topic in rock engineering.Rock engineering is a very complex dynamic state.In rock engineering,the stress in coal rock has always been a dynamic change process.This also shows that the loaded coal and rock mass in rock engineering has been in the loading state with different loading rates,so it is very important to study the change rule of mechanical properties of coal and rock samples under different loading rates.In this study,combined with acoustic emission monitoring technology,the mechanical properties of coal and rock samples under different loading rates and the acoustic emission signal law in the process of sample failure are studied.The mechanical properties and acoustic emission regulations of coal and rock samples under four groups of long-span loading rates of 0.6mm/min,0.3mm/min,0.6mm/min and 0.03mm/min under the condition of conventional laboratory displacement loading mode are studied Law.The test is divided into two groups,one is the experimental group of 4 coal samples,the other is the control group of 4 coal samples,the other is the control group of 4 rock samples,a total of 16 coal samples and retrograde test.The control group is set up to avoid the occasional error in the test process affecting the test results,and to study the coal rock sample force under different loading rates Learn properties and the law of acoustic emission signals.(1)Based on thevisco-elastoplastic mode,the mechanical properties of coal and rock samples are analyzed.It is found that the ultimate strength of coal and rock samples increases with the increase of loading rate.With the increase of loading rate,the elastic properties of coal and rock samples are more significant and the viscoplastic properties are weaker.In addition,through theoretical analysis,it is also found that the ultimate stress of coal rock specimen decreases with the increase of loading rate.(2)By analyzing the energy contained in the acoustic emission signal received by the acoustic emission system during the loading process of the sample,the acoustic emission signal is divided into two levels.The first type of acoustic emission signal: large amplitude acoustic emission signal,and the acoustic emission signal with amplitude greater than 0.1V.The large amplitude acoustic emission signal is generated by the large elastic crack in the loading process of coal and rock samples and the large crack formed by the micro crack penetration.This kind of signal represents the damage of large bearing structure in the loading process of samples.The second kind of acoustic emission signal: small amplitude acoustic emission signal,acoustic emission signal with amplitude between 0.01-0.1v.The small amplitude acoustic emission signal is generated by the elastic release of small energy during the loading process of the sample.This kind of acoustic emission signal represents the closure of the original open fracture and the formation of the micro fracture during the loading process of the coal rock sample.(3)It is found that the ultimate strength and modulus of elasticity of the samples increase with the increase of loading rate.And with the increase of loading rate,the ultimate strain of coal rock specimen when it reaches failure decreases,which is consistent with the results of mechanical model.(4)By analyzing the acoustic emission signal in the loading process of coal and rock samples,it is found that the invalid acoustic emission signal accounts for about 80%-90% of the total acoustic emission signal in the loading process,and the acoustic emission signal that represents the internal damage of the sample in the loading process only accounts for about 10%-20% of the total acoustic emission signal.This conclusion also just verifies the event or even the lack of the acoustic emission location event that lockner obtained 1% of the actual micro fracture in the sample.The effective signals represent less than 10% of the large amplitude signals of the internal large structural failure of coal rock samples,while the small amplitude signals representing the generation and penetration of microcracks account for more than 90% of the total signals.(5)It is found that with the increase of loading rate,the proportion of effective acoustic emission signal increases.However,with the increase of loading rate,the proportion of effective acoustic emission signal of coal sample is smaller than that of rock sample.In addition,it is found that the proportion of large amplitude acoustic emission signals in coal and rock samples decreases with the increase of loading rate.