木材压缩的四维原位层析成像
Wood compression in four-dimensional in situ tomography
摘要：
木材变形，特别是当受到压缩，表现出无尺度雪崩般的行为，以及依赖于结构的本地化的变形。我们已经采取了三维（3D）的X射线断层摄影在压缩与恒定应力率加载。使用数字体积相关，我们得到的局部总应变在实验过程中，并比较它的整体应变和声发射。木材细胞从最软的部分开始在整个样品中逐层塌陷，即，春天的木头随着损伤的进展，越来越多的软木层在整个样品中倒塌，这表明损伤扩散而不是局部化。在3D中，可以看到厚尾局部应变率分布，表明在软木层内部，损伤发生在局部点。所观察到的对数正态应变分布与独立的局部塌陷或不可逆变形事件的发展的这种观点是一致的。木材力学行为的一个关键特征是年轮之间局部变形的复杂相互作用。
英文摘要：
Wood deformation, in particular when subject to compression, exhibits scale-free avalanche-like behavior as well as structure-dependent localization of deformation. We have taken three-dimensional (3D) x-ray tomographs during compression with constant stress rate loading. Using digital volume correlation, we obtain the local total strain during the experiment and compare it to the global strain and acoustic emission. The wood cells collapse layer by layer throughout the sample starting from the softest parts, i.e., the spring wood. As the damage progresses, more and more of the softwood layers throughout the sample collapse, which indicates damage spreading instead of localization. In 3D, one can see a fat-tailed local strain rate distribution, indicating that inside the softwood layers, the damage occurs in localized spots. The observed log-normal strain distribution is in agreement with this view of the development of independent local collapses or irreversible deformation events. A key feature in the mechanical behavior of wood is then in the complex interaction of localized deformation between or among the annual rings.
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