L型结构木材中声发射信号传播特征

针对木材结构尺寸及介质改变对应变能传播的影响，研究应力波在变结构的L型试件中的声发射（acoustic emission,AE）特性。首先，参照ASTM-E976标准，在樟子松L型试件表面不同位置产生AE源，并利用采样频率为500 kHz的AE采集系统获取试件表面4个固定位置的AE信号。其次，依据小波分析原理对原始AE信号进行降噪并重构AE波形，进而研究木材结构变化对AE信号频域特征的影响。最后，基于对比分析，研究空气介质对于信号传播特性的影响。结果表明，当AE源位于锯材处时，信号以纵波和横波混合的形式单向传播，木材的结构变化主要影响低频信号成分，使得信号呈现高频带分布；而空气介质对于其时频域均有显著影响；当AE源位于薄板时，木材结构变化、传播路径及空气介质对于AE信号时频域特性均有显著影响。

Propagation Characteristics of Acoustic Emission Signals in L-Shaped Wood

The acoustic emission (AE) characteristics of the stress wave in L-shaped specimen with variable structures were studied in view of the influence of wood structure size and medium change on strain energy propagation.Firstly,with reference to the ASTM-E976 standard,AE sources were generated at different positions on the surface of the L-shaped specimen of Pinus sylvestris var.mongolica,and the AE acquisition system with a sampling frequency of 500 kHz was used to obtain the AE signals at four fixed positions on the surface of the specimens.Secondly,according to the principle of wavelet analysis,the original AE signals were de-noised and the AE waveform was reconstructed,and then the influence of wood structure on the frequency domain characteristics of the AE signal was examined.Finally,based on comparative analysis,the influence of air medium on signal propagation characteristics was studied.The results showed that when the AE source was located at the saw wood,the signal propagated in the form of a mixture of longitudinal and transverse waves,and the structural changes of wood mainly affected the low-frequency signal composition and made the signal appear high-frequency band distribution; while the air medium had a significant effect on its time-frequency domain.When the AE source was located in the thin plate,the wood structure changes,the propagation path and the air medium had significant effects on the frequency-domain characteristics of the AE signals.