单轴冲击荷载下煤体损伤及破坏特征分析

Analysis of damage and failure characteristics of coal under uniaxial impact loading

为探究单轴冲击荷载下煤体损伤破坏特性及演化规律,采用分离式霍普金森压杆(Split Hopkinson Pressure Bar)装置,通过调节储气室气压值,获得煤样在5 m/s冲击速度下的动力学响应结果,并以此为主要参考依据,确定模型细观物理力学参数;利用PFC3D软件,进行了在单轴冲击荷载作用下,含不同角度的闭合和非闭合直裂隙(0°、30°、60°、90°)的煤体在5 m/s冲击速度下,以及不含裂隙煤体在不同冲击速度下损伤破坏过程的数值模拟试验;探究了单轴冲击荷载下,冲击速度、裂隙分布角度等因素对煤体损伤破坏特征的影响。试验结果表明:冲击速度较低的时候,煤样主要遵循变形破坏准则,当冲击速度增长到一定程度时,则主要遵循强度破坏准则;裂隙通常由4个角和裂隙的尖端等介质突变处产生,呈现“V”形或“X”形扩展趋势,最终呈现出X形破坏带;煤样内外层呈现出不同的破坏形式,内层较于外层更接近三向应力状态,因此更容易发生剪切破坏,而外层就更容易发生拉伸破坏;总的来说,在单轴冲击荷载作用下,煤样主要破坏形式为拉伸破坏。

In order to investigate the damage characteristics and evolution of the coal body under uniaxial impact loading,a Split Hopkinson Pressure Bar(SHPB)device was used to obtain the kinetic response of the coal sample at an impact velocity of 5 m/s by adjusting the air pressure value of the storage chamber,and this was used as the main reference to determine the fine physical and mechanical parameter of the model.Using PFC3D software,numerical simulations of the damage process of coal bodies containing closed and unclosed straight fissures at different angles(0°,30°,60°,90°)under uniaxial impact loading at 5 m/s impact velocity,and coal bodies without fissures at different impact velocity conditions were carried out.The influence of factors such as impact velocity and fracture distribution angle on the damage characteristics of coal bodies under uniaxial impact loading was investigated.The test results show that:when the impact velocity is low,the coal sample mainly follows the deformation damage criterion,and when the impact velocity increases to a certain degree,it mainly follows the strength damage criterion;fissures are usually generated by the four corners and the tip of the fissure and other media mutations,showing a“V”or“X”shaped trend of expansion,eventually showing an X-shaped damage zone;the inner and outer layers of coal samples show different failure forms,the inner layer is closer to the triaxial stress state than the outer layer,so shear failure is more likely to occur,while the outer layer is more likely to occur tensile failure.Overall,under uniaxial impact loading,the main form of damage to coal samples is tensile damage.