School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo, China.
Henan Key Laboratory for Green and Efficient Mining & Comprehensive Utilization of Mineral Resources, Jiaozuo, China.
PLoS One. 2021 Jun 24;16(6):e0247908. doi: 10.1371/journal.pone.0247908. eCollection 2021.
To investigate the influence of bedding structure and different loading rates on the dynamic fracture characteristics and energy dissipation of Datong coal, a split Hopkinson bar was used to obtain the fracture characteristics of coal samples with different bedding angles. The process of crack initiation and propagation in Datong coal was recorded by the high-speed camera. The formula for the model I fracture toughness of the transversely isotropic material is obtained on the basis of the finite element method (FEM) together with the J-integral. By comparing the incident energy, absorbed energy, fracture energy and residual kinetic energy of Datong coal samples under various impact speeds, the energy dissipation characteristics during the dynamic fracture process of coal considering the bedding structure is acquired. The experimental results indicate that the fracture pattern of notched semi-circular bending (NSCB) Datong coal is tensile failure. After splitting into two parts, the coal sample rotates approximately uniformly around the contact point between the sample and the incident rod. The dynamic fracture toughness is 3.52~8.64 times of the quasi-static fracture toughness for Datong coal. Dynamic fracture toughness increases with increasing impact velocity, and the effect of bedding angle on fracture toughness then decreases. In addition, the residual kinetic energy of coal samples with the same bedding angle increases with the increase of impact speed. The energy utilization rate decreases continuously, and the overall dispersion of statistical data decreases gradually. In rock fragmentation engineering, the optimum loading condition is low-speed loading regardless of energy utilization efficiency or fracture toughness. These conclusions may have significant implications for the optimization of hydraulic fracturing process in coal mass and the further understanding of crack propagation mechanisms in coalbed methane extraction (CME). The anisotropic effect of coal should be fully considered in both these cases.
为了研究层理结构和不同加载速率对大同煤动态断裂特性和能量耗散的影响，采用分离式 Hopkinson 压杆（SHPB）获得了不同层理角度的煤样断裂特性。利用高速摄像机记录了大同煤裂纹起裂和扩展过程。基于有限元法（FEM）和 J 积分，获得了横观各向同性材料模型 I 断裂韧性的计算公式。通过比较不同冲击速度下大同煤样的入射能、吸收能、断裂能和残余动能，获得了考虑层理结构的煤动态断裂过程的能量耗散特性。实验结果表明，带有切口的半圆形弯曲（NSCB）大同煤的断裂模式为拉伸破坏。在分裂成两部分后，煤样大约以均匀的方式围绕着样条与入射杆之间的接触点旋转。大同煤的动态断裂韧性是准静态断裂韧性的 3.52~8.64 倍。动态断裂韧性随冲击速度的增加而增加，而层理角度对断裂韧性的影响则减小。此外，具有相同层理角度的煤样的残余动能随冲击速度的增加而增加。能量利用率不断下降，统计数据的整体分散度逐渐减小。在岩石破碎工程中，无论能量利用率还是断裂韧性，最佳加载条件都是低速加载。这些结论对于优化煤层水力压裂过程和进一步理解煤层甲烷开采（CME）中的裂纹扩展机制具有重要意义。在这两种情况下，都应充分考虑煤的各向异性效应。
