依据声发射事件信息熵对樟子松木材顺纹动态弹性模量的测算方法

Measuring Dynamic Modulus of Elasticity of Pinus sylvestris var.mongolica Litv.from Information Entropy of Acoustic Emission Events

以气干状态无明显缺陷的樟子松(Pinus sylvestris var.mongolica Litv)实木为试材,制成轴向800 mm、弦向60 mm、径向30 mm的试件(含水率12.8%,密度0.42 g/cm^(3));应用三思纵横UTM5105电子万能力学试验机对试件进行三点弯曲试验,在试件表面顺纹方向3个固定位置实时采集试件损伤过程的声发射(AE)信号;应用小波分析对原始声发射信号进行降噪并重构,确定声发射事件阈值,统计每秒的声发射事件数,再以6 s的声发射事件作为信息片段并计算其信息熵,依据每个信息片段信息熵辨识木材损伤过程;采用时差定位法确定声发射信号的顺纹传播速度,并依据木材各损伤阶段声发射信号顺纹传播的平均速度计算木材顺纹动态弹性模量。结果表明:当信息片段信息熵低于平均信息熵时说明木材进入了新的损伤阶段,试件损伤过程分为弹性阶段、塑性阶段、脆断阶段、后续断裂阶段;应用构建的依据声发射事件信息熵对木材顺纹动态弹性模量算法测试,试件损伤过程中,声发射信号顺纹传播平均速度为4915.8 m/s、相应的木材顺纹动态弹性模量为10.2 GPa。

The experiment was conducted to study the identification of wood damage process and the detection of wood’s dynamic modulus of elasticity,an algorithm for measuring wood’s dynamic modulus of elasticity parallel to grain from the information entropy of Acoustic Emission(AE)events was proposed.First,during the three-point bending loading test of Pinus sylvestris specimen,the AE signals of the specimen’s damage process were collected simultaneously at three fixed positions along the grain on the specimen’s surface.Then,the original AE signal was denoised and reconstructed by wavelet analysis,and the AE event threshold was set.Then the number of AE events per second was counted,and the 6-second AE events was took as an information fragment and its information entropy was calculated which was utilized to identify the specimen’s damage process.Finally,the AE signal’s propagation speed along the grain was obtained based on the time difference localization method,and the wood’s dynamic modulus of elasticity parallel to the grain was calculated according to its average speed of each damage stage of the wood.The results show that when the information fragment’s information entropy drops below the average information entropy,it indicates that the wood has entered a new damage stage,and the damage process of the specimen is divided into the elastic stage,the plastic stage,the brittle fracture stage and the subsequent fracture stage.During the damage process of the specimen,the average propagation velocity of the AE signal parallel to the grain is 4915.8 m/s,and the corresponding wood’s dynamic modulus of elasticity parallel to the grain is 10.2 GPa.