Stress wave propagation and attenuation of coal rock masses under static and dynamic loads
Firstly,the split Hopkinson pressure bar(SHPB)experimental system was employed to conduct impact tests on coal rock samples of short length(50 mm)and long length(300 mm)at various strain rates and different propagation distances,with strain gauges attached to various positions on the long samples.Secondly,a self-developed dry-coupled ultrasonic testing system was utilized to conduct ultrasonic tests at multiple stress levels and frequencies.Finally,the energy loss patterns during stress wave propagation in coal rock,as well as the attenuation patterns of high-frequency and low-frequency waves,were revealed.The results show that the peak values of incident,reflected and transmitted stress waves in the impact tests increase with the increase of strain rate.However,as the wave frequency increases with the increase of strain rate,high-frequency waves are more prone to attenuation when microscopic structural planes is traversed,resulting in a linear decrease in the transmission coefficient with the increase of strain rate.The transmitted waves exhibit a rapid attenuation within 300 mm of propagation,with a decay rate of up to 30%,followed by an approximately exponential attenuation pattern with further distance.In contrast,due to their small vibration amplitude and high frequency,ultrasonic waves rapidly attenuate when the propagation distance reaches 75 mm,with subsequent attenuation gradually leveling off.High frequencies are more likely to interact with the microscopic structure of coal rock and be absorbed,leading to faster attenuation of high-frequency waves with propagation distance.A linear relationship exists between frequency and the attenuation of wave amplitude.
stress waveultrasonic wavecoal rock masseswave propagationimpact loadingSHPB
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