Research on static and dynamic mechanical properties of spruce wood by three loading directions
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摘要: 利用INSTRON和Hopkinson压杆对含水率为12.72%, 密度为413kg/m^{3}云杉木材试件沿顺纹、横纹径向和横纹弦向进行准静态和动态压缩实验, 获得了云杉木材3个方向的抗压模量、准静态压缩应力应变曲线和3种应变率下的动态应力应变曲线. 结果表明云杉木材沿顺纹方向加载破坏形式表现为木材纤维轴向屈曲、褶皱; 横纹径向和弦向加载失效行为表现为木材纤维间的滑移破坏. 云杉顺纹方向抗压弹性模量最大, 分别约为横纹径向抗压弹性模量的21倍和横纹弦向抗压弹性模量的32倍; 横纹径向和弦向准静态压缩屈服应力基本相等, 试件沿顺纹方向准静态压缩屈服应力约为横纹径向和弦向屈服应力的9倍; 动态压缩屈服强度具有率敏感性, 在应变率为500-1000s^{-1}动态压缩实验中顺纹、横纹径向和弦向动压屈服强度均随着应变率的增加而显著提高. 同时对不同方向压缩下木材胞壁失效行为进行了理论分析, 表明产生完全压缩失效的平均极限载荷与胞壁屈服强度、胞元结构和产生的褶皱长度相关.
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关键词:
- 压缩实验
Abstract: Quasi-static and dynamic compression experiments ofspruce wood along axial, radial and tangential loading directions areimplemented by INSTRON and Hopkinson pressure bar equipments. Averagemoisture content and density of the spruce specimens are 12.72{\%} and413kg/m^{3}. Compression modulus and curves of quasi-static compressionstress versus strain are gained by static compression experiment. And therelation of dynamic stress versus strain is obtained by dynamic compressionexperiments with three strain rates. The experiment results show that thefailure modes of spruce specimens are fiber buckling and wrinkle whenloading direction is along the grain. When loading direction is along radialor tangential across to the grain, the failure modes is wood fiber slippageand delamination. Axial compression modulus is about twenty-one times asthat of radial across to the grain, and about thirty-two times as that oftangential across to the grain. Axial quasi-static compression yieldstrength is about nine times as that of radial and tangential across to thegrain. The radial and tangential quasi-static compression yield strengthsare almost equal. Dynamic compression yield strength of spruce wood issensitive to strain rate. The axial, radial and tangential dynamiccompression yield strengths increase greatly when strain rate is from500 to 1000s^{ - 1}. In addition, theory analytic solution tosingle wood cell failure under different direction compression is carriedout. The obtained expression shows that the mean limit loading is relativeto yield stress, cell structure dimension and wrinkle length for completewrinkle cases.-
Key words:
- compression experiment
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