Maaß Mona-Christin, Saleh Salimeh, Militz Holger, Volkert Cynthia A
Institute of Materials Physics, University of Göttingen, Friedrich-Hund-Platz 1, 37077, Göttingen, Germany.
Wood Biology and Wood Products, University of Göttingen, Büsgenweg 4, 37073, Göttingen, Germany.
Adv Mater. 2020 Apr;32(16):e1907693. doi: 10.1002/adma.201907693. Epub 2020 Mar 1.
The remarkable mechanical stability of wood is primarily attributed to the hierarchical fibrous arrangement of the polymeric components. While the mechanisms by which fibrous cell structure and cellulose microfibril arrangements lend stiffness and strength to wood have been intensively studied, the structural origins of the relatively high splitting fracture toughness remain unclear. This study relates cellulose microfibril arrangements to splitting fracture toughness in pine wood cell walls using in situ electron microscopy and reveals a previously unknown toughening mechanism: the specific arrangement of cellulose microfibrils in the cell wall deflects cracks from the S2 layer to the S1/S2 interface, and, once there, causes the crack to be repetitively arrested and shunted along the interface in a zig-zag path. It is suggested that this natural adaptation of wood to achieve tough interfaces and then deflect and trap cracks at them can be generalized to provide design guidelines to improve toughness of high-performance and renewable engineering materials.
木材卓越的机械稳定性主要归因于聚合物成分的分层纤维排列。虽然纤维细胞结构和纤维素微纤丝排列赋予木材刚度和强度的机制已得到深入研究，但相对较高的劈裂断裂韧性的结构起源仍不清楚。本研究利用原位电子显微镜将松木细胞壁中的纤维素微纤丝排列与劈裂断裂韧性联系起来，并揭示了一种前所未知的增韧机制：细胞壁中纤维素微纤丝的特定排列使裂纹从S2层偏向S1/S2界面，一旦到达该界面，会使裂纹反复受阻并沿界面呈锯齿形路径分流。有人认为，木材这种实现坚韧界面并在其上使裂纹偏向和捕获裂纹的自然适应性可以推广，以提供设计指南，提高高性能和可再生工程材料的韧性。
