Abstract When wood is split or cut along the grain, a reduction in tensile stiffness has been observed. The averaged mechanical properties of wood samples, veneers or splinters therefore change when their thickness is less than about 1 mm. The loss of stiffness increases as the thickness approaches that of a single cell. The mechanism of the effect depends on whether the longitudinal fission plane is between or through the cells. Isolated single cells are a model for fission between cells. Each cell within bulk wood is prevented from twisting by attachment to its neighbours. Separation of adjacent cells lifts this restriction on twisting and facilitates elongation as the cellulose microfibrils reorientate towards the stretching direction. In contrast when the wood is cut or split along the centre of the cells, it appears that co-operative action by the S1, S2 and S3 cell-wall layers in resisting tensile stress may be disrupted. Since much of what is known about the nanoscale mechanism of wood deformation comes from experiments on thin samples, caution is needed in applying this knowledge to structural-sized timber. The loss of stiffness at longitudinal fracture faces may augment the remarkable capacity of wood to resist fracture by deflecting cracks into the axial plane. These observations also point to mechanisms for enhancing toughness that are unique to wood and have biomimetic potential for the design of composite materials.

中文翻译：

---

木材的厚度相关刚度：潜在的机制和影响

摘要 当木材被劈开或沿纹理切割时，已观察到抗拉刚度降低。因此，当厚度小于约 1 毫米时，木材样品、单板或碎片的平均机械性能会发生变化。随着厚度接近单个细胞的厚度，刚度损失增加。该效应的机制取决于纵向裂变平面是在细胞之间还是穿过细胞。孤立的单细胞是细胞间裂变的模型。散装木材中的每个细胞都通过与相邻细胞的连接而防止扭曲。相邻细胞的分离解除了这种对扭曲的限制，并促进了伸长，因为纤维素微纤丝向拉伸方向重新定向。相比之下，当木材沿着细胞中心被切割或分裂时，似乎 S1、S2 和 S3 细胞壁层在抵抗拉伸应力方面的协同作用可能会被破坏。由于对木材变形的纳米级机制的大部分了解来自对薄样品的实验，因此在将这些知识应用于结构尺寸的木材时需要谨慎。纵向断裂面的刚度损失可能会通过将裂纹偏转到轴向平面来增强木材抵抗断裂的显着能力。这些观察结果还指出了增强木材独有的韧性的机制，并且具有用于复合材料设计的仿生潜力。在将这些知识应用于结构尺寸的木材时需要谨慎。纵向断裂面的刚度损失可能会通过将裂纹偏转到轴向平面来增强木材抵抗断裂的显着能力。这些观察结果还指出了增强木材独有的韧性的机制，并且具有用于复合材料设计的仿生潜力。在将这些知识应用于结构尺寸的木材时需要谨慎。纵向断裂面的刚度损失可能会通过将裂纹偏转到轴向平面来增强木材抵抗断裂的显着能力。这些观察结果还指出了增强木材独有的韧性的机制，并且具有用于复合材料设计的仿生潜力。