煤冲击破坏过程中的近距离瞬变磁场变化特征研究

通过分离式霍普金森杆动载实验装置和ZDKT–1型瞬变磁振测试系统，研究冲击速度为4.174～17.652 m/s条件下的煤冲击破坏过程中动力学特性和瞬变磁场变化特征。分别采用一维应力波理论和希尔伯特–黄变换对煤冲击过程中的应变信号和瞬变磁场变化信号进行分析研究。研究结果表明：(1) 在一定应变率范围内随着应变率的增加，煤材料的动态响应由硬化向软化过渡；(2) 煤动载冲击破坏过程中距离煤样4 cm处的区域内磁场发生明显变化，通过整体经验模式分解(EEMD)法分析发现，其持续时间小于2 s，频率为0～40 Hz；(3) 煤冲击破坏过程中瞬变磁场变化信号曲线表现为直线上升，指数下降，末尾小幅振荡的特征；(4) 煤的冲击破坏过程中瞬变磁场变化信号幅值，随着冲击速度、平均应变率、最大应变率、断裂应力极限值的增大均出现增大趋势，随着破坏应变的增加而减小，但实验数据的离散性较大。

CHARACTERISTICS OF TRANSIENT MAGNETIC NEARBY FIELD IN PROCESS OF COAL IMPACT DAMAGE

By a standard split Hopkinson pressure bar(SHPB) dynamic test device and ZDKT–1 type transient magnetic vibration test system,the dynamic properties of coal and the characteristics of the transient magnetic nearby field in the process of coal impact damage are researched under impact velocity of 4.174–17.652 m/s.The one-dimensional stress wave theory and the signal analysis of Hilbert-Huang transform(HHT) method are used to analyze the strain signal and the transient magnetic signal,respectively.The results show that:(1) The dynamic response of coal transforms from hardening to softening within certain range of strain rate;(2) The magnetic field has varied obviously in 4 cm distance of coal sample area during coal dynamic impact process,and it shows that the duration is less than 2 s and the frequency is less than 40 Hz through the ensemble empirical mode decomposition(EEMD) analysis;(3) The characteristics of the signal curve of the transient magnetic changes in coal impact damage process is shown that the first performance straight up,then exponential decline,at the end of small oscillation;(4) The amplitudes of transient magnetic field changes in coal impact damage process rises with the impact velocity,average strain rate,the maximum strain rate and the limit value of fracture stress increasing,while it reduces with the failure strain increasing,but the data are of a larger dispersion.