Mesoscale mechanics of wood cell walls under axial strain
Mesoscale mechanics of wood cell walls under axial strain
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DOI：
10.1039/c3sm50183c
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发表时间：
2013-01-01
期刊：
影响因子：
3.4
通讯作者：
Buehler, Markus J.
中科院分区：
文献类型：
--
作者：
Adler, David C.;Buehler, Markus J.
树木和其他木本植物是分层结构的，以实现广泛的机械性能-在各种不同的负载条件下生存所必需的-具有狭窄的化学成分范围。被理解为直接负责调节纵向弹性模量和屈服行为的层次水平是细胞壁的组成，其由嵌入半纤维素和木质素的无定形基质中的结晶纤维素原纤维组成。在这里，我们报告了一个简单的粗粒度模型的纤维素原纤维和半纤维素链提供自下而上的力学描述。我们确定了不同的原纤维角的力学行为，绘制力-应变关系，并将数据与实验结果和理论预测进行比较，从而深入了解木材的基本结构-性能关系。我们的模型表明，随着原纤维的剪切，半纤维素以粘滑运动变形，导致永久变形而不造成材料损坏，并随着变形的增加导致木材的特征软化。这项工作的主要贡献是开发了一个模型，可以微调和适应其他应用程序。虽然它提出了简单的配方，它可以成功地描述几个关键的现象，特别是三个制度的机械行为：弹性，塑性和高应变硬化，以及模量对微纤丝角的依赖性，并因此提供了一个自下而上的机械方法木材力学。
Trees and other woody plants are hierarchically structured to achieve a wide range of mechanical properties-necessary for their survival under various and varying loading conditions-with a narrow range of chemical composition. The hierarchical level understood to be directly responsible for modulating the longitudinal elastic modulus and yielding behavior is that of the composition of the cell walls, which consists of crystalline cellulose fibrils embedded in an amorphous matrix of hemicellulose and lignin. Here we report a simple coarse-grained model of the cellulose fibrils and hemicellulose chains to provide a bottom-up description of the mechanics. We identify the mechanical behaviors for varying fibril angles, plot force-strain relationships and compare the data with experimental results and theoretical predictions, providing insight into fundamental structure-property relations of wood. Our model shows that hemicellulose deforms in a stick-slip motion as the fibrils shear, resulting in permanent deformation without causing material damage, and leading to the characteristic softening of wood as deformation is increased. The main contribution of this work is the development of a model that can be fine-tuned and adapted to other applications. While it presents simple formulation, it can successfully describe several key phenomena, specifically the three regimes of mechanical behavior: elastic, plastic, and high-strain stiffening, as well as the dependence of modulus on the microfibril angle, and as such provides a bottom-up mechanistic approach to wood mechanics.