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预制孔洞煤样冲击力学特性及能量耗散试验研究

Experimental study on impact mechanical properties and energy dissipation of pre–drilled hole coal samples under impact load

  • 摘要: 为研究冲击载荷下预制孔洞煤样力学特性及能量耗散规律,制备含轴向孔洞的直径50 mm,高50 mm圆柱体煤样,利用分离式霍普金森压杆(SHPB)装置,开展8个孔洞尺寸和3个冲击气压水平的加载试验研究,借助平面场应变测量技术(VIC–2D)和高速摄像机,分析了冲击加载过程中试件动态应力、动态应变、裂纹演化、破坏失效及能量耗散特性。结果表明:①在试验涉及的孔洞直径范围内,冲击载荷下完整与孔洞煤样动态应力–应变过程均呈现微裂隙压密阶段、弹性阶段、塑性阶段和破坏阶段。同一冲击气压下,随孔径增大,煤样动态抗压强度、动态峰值应变均降低;孔径由0增大至8 mm时,煤样动态抗压强度和峰值应变下降出现快–慢分区特征。与完整煤样以拉伸裂纹破坏为主不同,孔洞煤样主要以拉伸裂纹–剪切裂纹复合破坏为主,且随着孔径增加,试件内部裂纹扩展能力变弱。②揭示了冲击载荷下孔洞煤样的能量耗散规律:孔洞煤样透射能、吸收能与孔径呈负相关,反射能与孔径呈正相关,这主要由孔洞改变试件过波面积造成。随孔径增大,煤样过波面积降低,其吸收能和透射能随之降低,与冲击载荷下孔洞煤样破碎度与孔径负相关结论相一致。研究成果有利于明晰冲击地压巷道钻孔卸压机理,为冲击地压防治提供理论支持。

     

    Abstract: In order to study the mechanical properties and energy dissipation law of pre–drilled coal samples under impact loads, the cylindrical coal samples with a diameter of 50 mm and a height of 50 mm containing axial holes were prepared. a split Hopkinson pressure bar (SHPB) was used to conduct loading experiments with 8 hole sizes and 3 impact pressure levels. Using plane field strain measurement technology (VIC–2D) and high-speed cameras, the dynamic stress, dynamic strain, crack evolution, failure modes and energy dissipation characteristics of the specimens were analyzed. The results indicate that the dynamic stress-strain curve of intact and porous coal samples under impact load exhibit micro crack compaction stage, elastic stage, plastic stage, and failure stage. Under the same impact pressure, as the hole size increases, the dynamic compressive strength and dynamic peak strain both decrease. When the diameter of the hole increases from 0 to 8 mm, the dynamic compressive strength and peak strain of the coal sample show a fast−slow zoning characteristic. Unlike intact coal samples which mainly exhibit tensile failure, porous coal samples mainly exhibit tensile-shear composite failure, and as the hole size increases, the internal crack propagation ability of the specimen weakens. In addition, this article reveals the energy dissipation law of coal samples with hole under impact loads. The transmitted energy and dissipated energy of coal samples with hole are negatively correlated with hole size, while the reflected energy is positively correlated with hole size. This is mainly caused by the changes in the wave impedance of the specimen caused by the hole. As the hole size increases, the wave impedance of the coal sample decreases, and its dissipated and transmitted energy also decrease, which is consistent with the conclusion that the fragmentation degree of coal samples under impact load is negatively correlated with the hole size. The research results are beneficial for clarifying the mechanism of drilling pressure relief in rock burst roadways and providing theoretical support for the prevention and control of rock burst.

     

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