声发射技术在木材受力破坏过程检测中的应用

利用声发射测试和力学实验相结合的方法，研究了东北常见的阔叶材树种山杨在动态载荷下的声发射演变过程；结合木材粘弹性特点，通过声发射参数分析研究该树种在不同受力阶段试件的声发射特点。最后得出以下结论：（1）径向纹理不通直的试件比通直的声发射撞击数要多，而且增加的趋势较快，但是在试件断裂前，声发射撞击数相差不大。（2）在试件断裂前，振铃计数和能量的变化小，局部极值出现在试件断裂附近，试件断裂后出现更多地局部极值；载荷急剧下降的点有振铃计数的急剧降低和能量的急剧升高与之对应。（3）随着时间和载荷的变化，声发射幅值参数值和撞击总数增加快慢可以体现材料在受力条件下的完全弹性、粘弹性和粘性三种状态。（4）声发射信号的声发射率和上升时间可以预测材料开始断裂进入危险期的和材料大量纤维断裂进入严重危险期的两个“临界点”。
关键词：无损检测，临界点，声发射，动态载荷，参数分析

Application of acoustic emission technology in damage process
 testing of wood under the dynamic loads
SUN Jian-ping   WANG Feng-hu
（Key Laboratory of Bio-based Material Science and Technology of Ministry of Education,
 Northeast Forestry University  Harbin 150040）

Abstract: The acoustic emission (AE) evolution process of David poplar (Poulus davidiana) samples was investigated by combining the two methods of mechanics testing and acoustic emission technique when the samples were imposed to the dynamic load. By analysis of AE parameters and the elastic-viscosity of wood, the AE characterization under different loads was explored. The results are: (1) Samples without straight radial grain have more hits and increasing faster than samples with straight radial grain, but before fracture hits count is not much different. (2) Before fracture ring count and energy have a little change and local maximum appears near fracture; After fracture there are much more local maximums and rapid drop of load is corresponded with rapid drop of ring count and rapid rise of energy. (3) With the time and load changing, the increase speed of AE cumulative hits and AE cumulative energy can exactly identify complete elasticity, elastic-viscosity and complete viscosity of wood, which of the three stages are the most important feature of wood under load. (4) The AE rate and rising time can be employed to predict two “critical points” of wood fracture damage. The first point means the material is in the state of slight danger and the second point means the material is in the state of serious danger.
Keywords: Non-destructive testing; Critical point; Acoustic emission; Dynamic loads; Parameter analysis