Study on time-frequency characteristics of acoustic-charge signals in fracture and crack evolution process of coal and rock

In order to investigate the acoustic-charge physical signal law of coal and rock fracture crack evolution process,the monitoring test of whole process acoustic-charge signals of coal rock samples failure under uniaxial compression condition was carried out.The time-frequency domain characteristics of acoustic-charge signals in different stages of crack evolution of coal and rock samples are analyzed and the correlation parameters of acoustic-charge signals are quantitatively analyzed.The results show that the evolution process of fracture crack of coal and rock goes through the stages of “micro-fracture”,“secondary fracture” and “main fracture” in turn,and the stress mutation and the generation and change of acoustic- charge signals are consistent in each stage.As the crack evolves,the mean peak value of charge signals and acoustic emission energy of coal and rock samples increase gradually.And the high value charge and acoustic emission signal are produced simultaneously,which indicates that the coal and rock are in the stage of “secondary rupture”,which can be used as the precursor information of coal and rock near instability failure.The effect of crack evolution on the charge amplitude of coal samples is greater than that on acoustic emission energy amplitude.With the evolution of crack in coal and rock samples,the main frequency of acoustic-charge signal gradually changes to low frequency,and the amplitude of main frequency increases gradually.Therefore,the decreasing of main frequency and the increasing trend of the amplitude of main frequency can be regarded as the precursor characteristics of the instability and failure of coal and rock.The influence of different evolution stages of cracks on the main frequency amplitude of acoustic emission energy of rock samples is greater than that of coal samples.