针对木材各向异性所导致的同一声发射(acoustic emission,AE)源在不同方向上传播速率各异的问题,研究了同一AE源在4个不同方向上发出的AE信号波形特征和传播速率随角度变化的规律。首先,采用0.7mm铅芯折断方式模拟声发射源,在马尾松胶...针对木材各向异性所导致的同一声发射(acoustic emission,AE)源在不同方向上传播速率各异的问题,研究了同一AE源在4个不同方向上发出的AE信号波形特征和传播速率随角度变化的规律。首先,采用0.7mm铅芯折断方式模拟声发射源,在马尾松胶合木表面沿纹理方向顺时针每隔15°,通过采样频率为500 k Hz的四通道高速采集系统收集原始AE信号。然后,基于小波分析的方法从原始信号中重构AE信号波形,根据小波变换原理和AE传感器的分辨范围,采用daubechies小波进行5层小波分解,在分析各层高频细节信号时频域特征的基础上进行AE信号波形重构。最后,利用信号相关性分析的方法确定AE信号,通过2个传感器的时差,进而采用时差定位法计算AE信号的传播速度。对于不同方向的AE传播速率,通过多项式拟合的方法,提出AE传播速度随角度变化的函数关系。展开更多
By using MTS815 rock mechanics test system,a series of acoustic emission(AE) location experiments were performed under unloading confining pressure,increasing the axial stress.The AE space-time evolution regularities ...By using MTS815 rock mechanics test system,a series of acoustic emission(AE) location experiments were performed under unloading confining pressure,increasing the axial stress.The AE space-time evolution regularities and energy releasing characteristics during deformation and failure process of coal of different loading rates are compared,the influence mechanism of loading rates on the microscopic crack evolution were studied,combining the AE characteristics and the macroscopic failure modes of the specimens,and the precursory characteristics of coal failure were also analyzed quantitatively.The results indicate that as the loading rate is higher,the AE activity and the main fracture will begin earlier.The destruction of coal body is mainly the function of shear strain at lower loading rate and tension strain at higher rate,and will transform from brittleness to ductility at critical velocities.When the deformation of the coal is mainly plasticity,the amplitude of the AE ringing counting rate increases largely and the AE energy curves appear an obvious ''step'',which can be defined as the first failure precursor point.Statics of AE information shows that the strongest AE activity begins when the axial stress level was 92-98%,which can be defined as the other failure precursor point.As the loading rate is smaller,the coal more easily reaches the latter precursor point after the first one,so attention should be aroused to prevent dynamic disaster in coal mining when the AE activity reaches the first precursor point.展开更多
文摘针对木材各向异性所导致的同一声发射(acoustic emission,AE)源在不同方向上传播速率各异的问题,研究了同一AE源在4个不同方向上发出的AE信号波形特征和传播速率随角度变化的规律。首先,采用0.7mm铅芯折断方式模拟声发射源,在马尾松胶合木表面沿纹理方向顺时针每隔15°,通过采样频率为500 k Hz的四通道高速采集系统收集原始AE信号。然后,基于小波分析的方法从原始信号中重构AE信号波形,根据小波变换原理和AE传感器的分辨范围,采用daubechies小波进行5层小波分解,在分析各层高频细节信号时频域特征的基础上进行AE信号波形重构。最后,利用信号相关性分析的方法确定AE信号,通过2个传感器的时差,进而采用时差定位法计算AE信号的传播速度。对于不同方向的AE传播速率,通过多项式拟合的方法,提出AE传播速度随角度变化的函数关系。
文摘By using MTS815 rock mechanics test system,a series of acoustic emission(AE) location experiments were performed under unloading confining pressure,increasing the axial stress.The AE space-time evolution regularities and energy releasing characteristics during deformation and failure process of coal of different loading rates are compared,the influence mechanism of loading rates on the microscopic crack evolution were studied,combining the AE characteristics and the macroscopic failure modes of the specimens,and the precursory characteristics of coal failure were also analyzed quantitatively.The results indicate that as the loading rate is higher,the AE activity and the main fracture will begin earlier.The destruction of coal body is mainly the function of shear strain at lower loading rate and tension strain at higher rate,and will transform from brittleness to ductility at critical velocities.When the deformation of the coal is mainly plasticity,the amplitude of the AE ringing counting rate increases largely and the AE energy curves appear an obvious ''step'',which can be defined as the first failure precursor point.Statics of AE information shows that the strongest AE activity begins when the axial stress level was 92-98%,which can be defined as the other failure precursor point.As the loading rate is smaller,the coal more easily reaches the latter precursor point after the first one,so attention should be aroused to prevent dynamic disaster in coal mining when the AE activity reaches the first precursor point.
