Why don't branches snap? The mechanics of bending failure in three temperate angiosperm trees
Why don't branches snap? The mechanics of bending failure in three temperate angiosperm trees
复制标题
DOI：
10.1007/s00468-011-0650-y
复制
发表时间：
2012-06-01
影响因子：
2.3
通讯作者：
Ennos, A. R.
中科院分区：
文献类型：
--
作者：
van Casteren, A.;Sellers, W. I.;Ennos, A. R.
活树枝几乎不可能折断。有些显示“绿枝骨折”，打破了一半，然后分裂沿着他们的长度，而其他人只是扣。在这项研究中，我们调查了三个温带被子植物：白蜡，白蜡树，榛，欧洲榛和白色杨柳，白柳矮林树枝弯曲破坏。我们进行了弯曲试验，并对木材的结构、密度、拉伸和压缩强度进行了一系列观察，以了解破坏模式。这三个物种表现出对比鲜明的行为;杨柳屈曲，而灰显示干净的绿枝骨折和榛更广泛的绿枝骨折。这些差异可能与其木材性质有关。杨柳弯曲是因为它的轻质木材具有非常低的横向抗压强度，特别是切向抗压强度，并且被横向应力压碎。虽然其他树种在凹面的纵向压缩中屈服，但在弯曲时凸面的拉伸中最终失败，因为它们的高密度木材更好地抵抗横向压缩。然而，由于其木材的切向抗拉强度较低，裂纹沿中线向下转移。白蜡木和榛木的断裂差异与其木材解剖学和力学的细微差别有关。
Living tree branches are almost impossible to snap. Some show "greenstick fracture", breaking halfway across before splitting along their length, while others simply buckle. In this study we investigated the bending failure of coppice branches of three temperate angiosperm trees: ash, Fraxinus excelsior; hazel, Corylus avellana; and white willow, Salix alba. We carried out bending tests, and made a series of observations on the structure, density and tensile and compressive strength of their wood to understand the pattern of failure. The three species showed contrasting behaviour; willow buckled whereas ash showed clean greenstick fracture and hazel a more diffuse greenstick fracture. These differences could be related to their wood properties. Willow buckled because its light wood had very low transverse compressive strength, particularly tangentially and was crushed by transverse stresses. Though the other species yielded in longitudinal compression on the concave side, they ultimately failed in tension on the convex side when bent because their higher density wood resisted transverse compression better. However, the crack was diverted down the midline because of the low tangential tensile strength of their wood. Differences in fracture between ash and hazel are related to fine-scale differences in their wood anatomy and mechanics.