基于声发射的樟子松锯材表面横波与内部纵波传播特性及能量衰减规律

Propagation Characteristics and Energy Attenuation Law of Surface Shear Waves and Internal Longitudinal Waves in Mongolian Scotch Pine Sawn Timber Based on Acoustic Emission

为研究不同声发射(acoustic emission,AE)模态的传播特性与能量衰减模式,依据波动理论提出一种木材AE信号表面横波与内部纵波析取方法,进而建立AE信号能量衰减模型。首先,依据ASTM-E976-2015通过铅芯折断的方式在樟子松锯材表面产生AE源,并在不同位置采集表面横波与内部纵波的AE原始信号,采样频率设置为500 kHz;然后,采用小波分析方法从原始信号中重构AE波形,分析木材AE信号表面横波与内部纵波的传播特性;最后,通过指数函数拟合的方法,构建表面横波与内部纵波能量衰减模型。结果表明:表面横波与内部纵波在樟子松锯材中传播时AE能量均呈明显的指数衰减规律,但在频率分布和传播速率上均有较大差异。表面横波在传播初始阶段主要分布在以80.0 kHz和113.3 kHz为中心的两个中高频段内,随着其在木材表面的传播,高频信号迅速衰减为低频信号。而内部纵波始终处于相对低频段内,其平均传播速率约为表面横波的4.6倍。

In order to study the propagation characteristics and energy attenuation modes of different acoustic emission(AE)modes,a method for extracting surface shear waves and internal longitudinal waves of wood AE signals was proposed based on the wave theory.The AE signal energy attenuation model was established.First,according to the ASTM-E976-2015,the AE source was generated on the surface of the sawn timber of Pinus sylvestris var.mongolica Litv.by breaking the lead core,and the AE raw signals of the surface transverse wave and the internal longitudinal wave were collected at different positions with the sampling frequency of 500 kHz.Then,the wavelet analysis method was used to reconstruct the AE wave-form from the original signal;the propagation characteristics of the surface shear wave and the internal longitudinal wave of the wood AE signal were investigated.Finally,an exponential function fitting method was used to construct the energy attenuation model of surface shear waves and internal longitudinal waves.The results showed that the AE energy of both the surface transverse wave and the internal longitudinal wave exhibited a significant exponential decay law when propagating in the wood;there were big differences in frequency distribution and propagation rate.In the initial stage of propagation,the surface transverse wave was mainly distributed in the two middle and high frequency bands centered at 80.0 kHz and 113.3 kHz.As it propagated on the surface of the wood,the high-frequency signal quickly attenuated to the low-frequency signal.The internal longitudinal wave was always in a relatively low frequency band,and its average propagation velocity was about 4.6 times that of the surface transverse wave.