摘要
木材多尺度结构主要包括纳米级高分子结构、微米级细胞壁多层结构和毫米级生长轮结构。纳米级高分子结构中三大素(纤维素、半纤维素和木质素)性质各异,微米级细胞壁多层结构中细胞壁各层三大素含量和微纤丝角不同,毫米级生长轮结构中细胞类型、大小和排列方向存在差异,这些结构差异均会导致多尺度结构单元之间的力学性质各异。木材破坏过程主要包括初始裂纹萌生和裂纹扩展,裂纹萌生和扩展主要由木材不同尺度单元间结构和力学性质的差异以及木材内部缺陷的不规则演化决定。本研究综述木材不同尺度单元间的结构和力学性质差异,并分析结构差异对木材破坏的影响。同时,提出今后有关木材多尺度结构差异对其破坏影响研究的几点建议:1)深入解译木材微纳结构的性质差异,研究木材三大素的排列取向规律以及木材不同化学组分对外部载荷的响应差异,揭示壁层内三大素的变形机制;研究细胞壁各层化学组分分布以及微纤丝取向不同导致的力学性能差异,分析外载荷作用下各壁层之间存在的应力传递规律;2)研究不同载荷作用下木材生长轮结构和细胞壁结构的裂纹萌生和扩展规律,精准定位木材破坏过程中不同尺度结构的裂纹萌生位置,区分裂纹在不同木材组织内部扩展时破坏断面的细胞破坏模式;3)借助有限元分析等理论方法,研究木材不同尺度单元间结构差异对木材生长轮结构和细胞壁结构上应力分布规律和应力集中位置的影响,揭示木材多尺度结构差异对木材破坏的影响机制。
Wood multiscale structures are usually described at three different structural levels from nanometer to millimeter,including nanoscale polymer structure,microscale multilayer structure and macroscale growth ring structure.There were differences between these multiscale hierarchical structures,including the structures and properties of wood polymers;polymer contents and microfibril angles(MFAs)of different cell wall layers;cell types,sizes and arrangement orientation in growth ring structure.Those structure differences lead to differences in mechanical properties between multiscale hierarchical structure elements.Furthermore,the processes of wood fracture include crack initiation and propagation,which are related to structure and mechanical properties differences between multiscale hierarchical structure elements and irregular evolution of“natural defects”.In this paper,the structures and mechanical properties differences of multiscale hierarchical structure elements,the effects of those differences on wood fracture were reviewed.Meanwhile,it should be studied from the following aspects in the future:1)The properties differences of wood micro-and nano-scale structure.Molecular deformations of wood polymers are revealed by the differences of arrangement orientation and response to load of wood polymers.The mechanical properties differences and stress transfer mechanism between wall layers due to the difference of wood polymers distribution and orientation of microfibrils in each layer of cell wall should be analyzed.2)The crack initiation and propagation of growth ring and cell wall structure are studied,and cell fracture types of different fracture surface also are pointed out.3)The effects of structure differences between multiscale hierarchical structure elements on the stress distribution and stress concentration of wood growth ring and cell wall structures are analyzed that will be revealed the influence mechanism of multi-scale structure difference on wood fracture.
作者
王东
林兰英
傅峰
Wang Dong;Lin Lanying;Fu Feng(Research Institute of Wood Industry, CAF, Beijing 100091;College of Materials Science and Engineering, Nanjing Forestry University, Nanjing 210037)
出处
《林业科学》
EI
CAS
CSCD
北大核心
2020年第8期141-147,共7页
Scientia Silvae Sinicae
基金
国家自然科学基金面上项目(31770597)。
关键词
木材
多尺度结构
差异
破坏
wood
multiscale structure
differences
fracture
