• 论文与研究报告 •

### 动态测试木材的泊松比

1. 1. 南京林业大学材料科学与工程学院 南京 210037;
2. 南京林业大学机械电子工程学院 南京 210037
• 收稿日期:2014-02-27 修回日期:2014-06-30 出版日期:2015-05-25 发布日期:2015-06-11
• 基金资助:
2013—2014年江苏高校优势学科建设工程项目资助(PAPD)。

### Experimental Study on Poisson's Ratio of Lumber by Dynamic Testing

Wang Zheng1, Gu Lingling2, Gao Zizhen1, Liu Bin2, Wang Yunlu1

1. 1. College of Materials Science and Engineering, Nanjing Forestry University Nanjing 210037;
2. College of Mechanical and Electronic Engineering, Nanjing Forestry University Nanjing 210037
• Received:2014-02-27 Revised:2014-06-30 Online:2015-05-25 Published:2015-06-11

Abstract: 【Objective】 Based on the first bending mode shape of cantilever slab, this work proposed a method for dynamic testing of lumber Poisson's ratio. In this paper, this method was used to measure Poisson's ratio of Sitka Spruce (Picea sitchensis) lumbers along and across grain on radial section and across grain on transverse section. Based on the testing results, the accuracy is analyzed with testing results of elastic modulus, calculated by substituting the first-order bending frequency, measured with cantilever plate specimen, into cantilever formula. Meanwhile, dynamic testing of mild steel plate was conducted to verify the correctness of the dynamic method of testing for lumber MOE. 【Method】Based on the theory of structural dynamics, free vibration of cantilever specimen of Sitka Spruce lumbers and mild steel can be stimulated by knocking, and the fundamental vibration should be reserved by filtering processing. Additionally, decaying curve of oscillatory waves for transverse and longitudinal strain of fundamental vibration should also be recorded and displayed. Besides, Poisson's ratio can be obtained from the ratio between transverse strain peak and longitudinal strain peak at the same time. 【Result】 It is seen that the positive (negative) peak in oscillatory wave curve for transverse strain is corresponding to that for longitudinal strain, meaning that the phase difference, between oscillatory wave curves for transverse strain and longitudinal strain, is 180°, or that transverse strain and longitudinal strain are in reverse. According to verification test of mild steel, the average value should be taken after calculating the ratios between peak-to-peak values read from the first channel and the second channel in oscillatory wave curve. Finally, the measurement of Poisson's ratio of low-carbon steel should be μ =0.28 (the standard value is 0.25-0.28). The ratio, between μLR, (Poisson's ratio of grain at radial section) to μRL(Poisson's ratio of stripe at radial section) is 10.6, which means the Poisson's ratio of grain at radial section is one order higher than that of stripe at radial section. Elastic modulus calculated with cantilever formula is 0.7% smaller than the actual one.【Conclusion】 The dynamic method for Poisson's ratio measurement with the first-order bending mode shape of cantilever plate is proved to be feasible, efficient and highly accurate; Poisson's ratio of grain at radial section of Sitka Spruce is one order higher than that of stripe at cross section, which represents the anisotropy of lumber; The elastic modulus is sufficiently accurate by substituting the first-order fixed frequency, measured with the cantilever plate of Sitka Spruce specimen, into cantilever theoretical equation.