马尾松胶合木表面声发射信号各向异性传播规律

Anisotropic propagation of acoustic emission signal on surface of Pinus massoniana Lamb. glulam

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。

As one of the natural resources,wood can be recycled and has green,environmental protection,energy saving and other characteristics,which is always been an important building material. Especially,wood is under the category of natural biopolymers. Since it is desirable to build a sustainable society based on renewable and sustainable resources,wood may be considered as a future-oriented material for residential and commercial structures in the world.At present,wood structure building has been widely used in residential,commercial and industrial projects. As a result,timber stress monitoring is especially important. To solve the problem that different propagation rates of acoustic emission( AE) signal generated by the same AE source resulted from the anisotropic of the wood,thus to provide a basis for the stress monitoring and the AE source location of wood,the law of the AE on the surface of the glulam and the rate of the velocity of the transmissions were investigated in this study. Firstly,the sound emission source was simulated by breaking the lead core of 0.7 mm,and the original AE signal was collected at a 4-channel high speed acquisition system with a sampling frequency of 500 kHz at a sampling frequency of 15° in the grain direction on the surface of Pinus massoniana plywood. Then,the reconstructed AE waveform from the original signal based on the analysis of tiny wavelets and according to the principle of wavelet transform and the AE sensor resolution range,we used the daubechies wavelet to make 5-layers of wavelet decomposition,and to analyze the frequency domain signature on the frequency signature of each layer of high-frequency detail and reconstructed the AE waveform. Finally,we used the correlation analysis method to determine the time difference between AE signal and the signal through two sensors and used the time difference location method to calculate the speed of the AE signal. For the different directions of the AE propagation rate,using the polynomial fitting method,a function of the AE propagation velocity changing with angle was put forward.