冲击载荷下两种应变率作用方式煤岩能量演化及分形特征研究

Energy evolution and fracture characteristics of coal and rock under impact load with two kinds of strain rate action modes

为探究不同驱动气压(0.3~0.5 MPa)和试样长度(15~50 mm)下煤岩能量演化及分形特征,利用Φ50 mm分离式霍普金森压杆(split Hopkinson pressure bar,SHPB)系统进行了动态压缩试验,明确了两种方式下能量演化参数随应变率的变化规律,基于分形理论探讨了破碎试样的分形特征,并揭示了不同应变率下煤岩破碎与能量演化的内在联系。结果表明:应变率随驱动气压升高呈线性增加,随试样长度增加呈幂函数降低;不同驱动气压和试样长度下的破碎耗能和破碎耗能密度随应变率升高分别呈指数和线性形式增加,且推断存在某一应变率,使两种方式破碎耗能密度的率敏感性趋于一致;气压改变和试样长度改变下的平均粒径随应变率升高均呈幂函数形式降低,而分形维数分别呈线性和指数形式增加;试验过程中随着应变率增加,试样破碎程度加剧,分形维数增大,且作用方式作为影响分形维数的重要因素,对结果起到了关键作用。研究结果可为采场合理布置施工参数提供一定参照。

In order to explore the energy evolution and fractal characteristics of coal and rock under different driving pressure(0.3-0.5 MPa)and sample length(15-50 mm),dynamic compression tests were carried out by using a split Hopkinson pressure bar(SHPB)equipment with a diameter of 50 mm,and the variation of energy evolution along with the strain rate under two different action modes was clarified.The fractal characteristics of broken samples were discussed based on the fractal theory,and the inherent relationship between coal and rock crushing and energy evolution under different strain rates was revealed.The results show that the strain rate increases linearly with the increase of driving pressure and decreases with a power function with the increase of sample length;the crushing energy consumption and crushing energy density under different driving pressure and sample length increase exponentially and linearly respectively with the increase of strain rate,and it is inferred that there is a certain strain rate,which makes the rate sensitivity of crushing energy density under the two action modes tend to be consistent;the average particle size decreases with the increase of strain rate with a power function,while the fractal dimension increases linearly and exponentially with increasing strain rate as pressure changes and sample length changes respectively;during the test,with the increase of strain rate,the fragmentation degree of the sample intensifies and the fractal dimension increases and the action mode,as an important factor affecting the fractal dimension,plays a key role in the results.The research results provide some reference for the reasonable layout of stope construction parameters.