动静荷载下煤岩体应力波传播与衰减特征

Stress wave propagation and attenuation of coal rock masses under static and dynamic loads

首先,采用霍普金森压杆(SHPB)试验系统对短试样(长度为50 mm)和长试样(长度为300 mm)煤岩开展多种应变率和不同传播距离的冲击试验,并将应变片粘贴在长试件的不同位置;其次,结合自主研发的干耦合式超声波测试系统开展多应力水平和多频率的超声波测试试验;最后,揭示应力波在煤岩传播过程中的能量损失规律以及高频波与低频波的衰减规律。研究结果表明:在冲击试验中,入射、反射及透射应力波峰值均随应变率增加而增大,但由于应变率增加时波频率增加,高频波在穿越微观结构面时更易衰减,透射系数随应变率增加而呈线性减小;透射波在传播距离300 mm以内衰减较快,衰减量达30%,透射波随距离增加大致而呈现指数形式的衰减规律;超声波由于振动幅值小且频率高,在传播过程中距离达到75 mm时迅速衰减,之后的衰减幅度逐渐趋于平缓。高频率更易与煤体的细观结构发生相互作用而被吸收,致使高频波随传播距离衰减更快,频率与波幅值衰减呈线性关系。

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.