应压木细胞壁S_(2)层的微纤丝螺旋角对其抗压韧性的影响  

Effects of microfibril helix angle in the S_(2)layer of compression wood cell wall on the compressive toughness of it

作　　者：刘浩正 王建山[1] 石广玉[1] Liu Haozheng;Wang Jianshan;Shi Guangyu(Department of Mechanics,School of Mechanical Engineering,Tianjin University,Tianjin 300354,China)

机构地区：[1]天津大学机械工程学院力学系,天津300354

出　　处：《北京林业大学学报》2023年第4期136-146,共11页Journal of Beijing Forestry University

基　　金：国家自然科学基金重点国际合作研究项目(1202010100)。

摘　　要：【目的】应压木细胞壁S_(2)层中的大微纤丝螺旋角(MFA)是树木管胞对力学环境适应性生长的结果,故它有其特别的力学性能。但目前人们还不了解S_(2)层中大MFA对其抗压性能的增韧机理。基于应压木细胞壁S_(2)层的超微结构建立复合材料力学模型,采用数值模拟方法研究应压木细胞壁S_(2)层中MFA对其抗压韧性的影响,可以探究其中的力学机理,并探索基于数值模型研究木细胞壁压缩韧性的建模与分析方法,进而为仿生材料设计奠定力学基础。【方法】首先将云杉木细胞壁S_(2)层简化为连续微纤丝和基体组成的复合材料,并利用夹杂理论的自洽模型计算木细胞壁S_(2)层基体的等效弹性常数。然后利用HyperWorks建立木细胞壁的纤维增强复合材料有限元分析模型,用Abaqus模拟不同MFA的应压木和正常木细胞壁S_(2)层在压缩载荷下的力学行为,并用所得结果分析其MFA与抗压韧性的关系。在此基础上,对比是否考虑木细胞壁的S_(1)、S_(3)(或S_(2)L,指的是S_(2)层与S_(1)层之间木质素和半纤维素含量高的区域)和MP层(P和ML层)对其受压力学行为的影响,并分析在应压木细胞壁数值模型中考虑各组分材料塑性行为的重要性。【结果】在压力作用下,当木细胞壁S_(2)层的MFA在0°~45°内增大时,其临界屈曲位移增大,临界屈曲压力先减小再增大。45°MFA应压木细胞壁S_(2)层的临界压力与0°MFA正常木细胞壁S_(2)层相当,但前者的临界屈曲位移是后者的3.57倍,屈曲失稳前的应变能是后者的2.95倍。在相同压力下,45°MFA应压木细胞壁S_(2)层微纤丝的von Mises应力低于0°MFA正常木。由于单个应压木细胞壁S_(2)层中螺旋状微纤丝所具有的压−扭耦合变形受到周边管胞对扭转变形的约束,其抗压刚度和抗压韧性得到增强。应压木细胞壁中的S 1、S_(2)L和MP层对其受压屈曲有显著的约束作用,完整应压木细胞壁的临[Objective]The large microfibril helix angle(MFA)in the S_(2)layer of the compression wood cell wall is the result of the adaptive growth of tree tracheids to the mechanical stimulation,so it has special mechanical functions.However,the toughening mechanism of large MFA in S_(2)layer on the compressive properties of wood cell wall has not been understood yet by researchers.Based on a computational model of composite material for the ultrastructure of S_(2)layer of the compression wood cell wall,the effects of MFA in S_(2)layer on the compressive toughness of compression wood cell wall were simulated and the toughening mechanism was explored,and the method of modeling and analyzing the compressive toughness of the wood cell wall based on the numerical model was explored.The findings presented in this paper would provide useful guideline for the optimal design of biomimetic materials.[Method]First,the S_(2)layer of spruce wood cell wall was modeled as a composite cylinder composed of continuous microfibrils as well as matrix,and the equivalent elastic constants of the matrix of S_(2)layer were calculated using the self-consistent model of inclusion theory.Then,the finite element analysis model of the fiber reinforced composite of wood cell wall was established by HyperWorks.The compressive mechanical behaviors of the S_(2)layers of compression wood and normal wood with different MFA were simulated by Abaqus,and the relationship between MFA and the compressive toughness of S_(2)layer was analyzed.On this basis,the compressive mechanical behaviors of wood cell wall with and without S_(1),S_(3)(or S_(2)L,it means the area between S_(2)and S_(1) layer with high lignin and hemicellulose content)and MP(P and ML)layers were investigated,and the importance of considering the plastic behavior of each constituent in the numerical model of compression wood cell wall was analyzed.[Result]As the increasing of MFA(0°~45°)in S_(2)layer,the critical buckling displacement of S_(2)layer of wood cell wall was increasing,and the cri

关 键 词：应压木 木细胞壁 微纤丝角(MFA) 临界屈曲位移 抗压韧性 增韧机理 数值模拟 

分 类 号：S781.29[农业科学—木材科学与技术] S781.1[农业科学—林学] O242.2[理学—计算数学]