【作者】 张波；

【导师】 费本华；

【作者基本信息】 中国林业科学研究院 ， 木材科学与技术， 2007， 硕士

【摘要】 木材是由多细胞组成的具有复杂层状结构和特殊分子力学现象的生物复合材料。木材的宏观力学行为与细胞形态、细胞力学性质、细胞间的连接方式以及细胞构成木材的几何方式密切相关。研究木材细胞的形态、结构和力学性能，对于在管胞和分子水平运用力学原理建立多细胞相互作用的力学模型，最终把握木材的力学行为机理有重要意义。本文以组织结构较为简单的针叶材马尾松为研究对象，在总结归纳木材微观力学领域研究进展的基础上，系统研究了马尾松管胞形态、微纤丝角度、管胞纵向力学性能以及管胞壁层力学性能，在此基础上探讨了马尾松管胞形态与管胞力学性能之间的关系。主要内容包括：马尾松管胞形态参数(长度、宽度、长宽比、径向直径、弦向直径、壁厚)以及微纤丝角度在径向、纵向和生长轮内的变异规律；管胞的纵向抗拉强度在径向、纵向和生长轮内的变异及其与管胞形态之间的关系；管胞壁层纳米压痕弹性模量、硬度在壁层厚度方向上的的变化及其与结构的关系。得到如下结论：(1)马尾松管胞长度径向变异：从髓心向外至第8生长轮管胞长度呈线性增加；8-14生长轮管胞长度不规则变化并达到一较高值；14生长轮后管胞长度略有减小，总体趋于稳定。马尾松管胞长度符合正态分布，幼龄材部位60％的管胞长度分布约为2500μm—4000μm，成熟材70％的管胞长度分布在4000μm—5500μm。管胞宽度从髓心向外总体呈递增趋势，到第8生长轮时逐渐趋于平缓。髓心附近管胞宽度最小为40μm；成熟材部位管胞宽度，3m高度处为45μm；6m高度处为50μm；9m高度处为55μm。马尾松管胞的长宽比在近髓心处最小为55，髓心向外至第8生长轮管胞长宽比呈线性增加达到80，第8生长轮后趋于稳定，介于80—100。管胞的弦向直径在生长轮内较为稳定，早材直径略大于晚材，范围在40μm—45μm之间；径向直径早材显著大于晚材，早材径向直径在60μm左右，晚材仅为20μm。管胞的双壁厚在5μm—15μm，其中早材部位较薄为5μm，向晚材逐渐增加至15μm。(2) X射线衍射法测定木材微纤丝角迅速、可靠，适于大量试样的测试，可以实现木材微纤丝角变异的系统研究。基于Origin软件的高斯函数法，物理意义明确，实现了对衍射谱的去噪、拟合的计算机快速实现。马尾松木材在所有高度上髓心处微纤丝角较大，均在20°—35°，向外至第8生长轮微纤丝角呈线性减小，8至14生长轮微纤丝角缓慢减小或者不稳定变化，14年以后微纤丝角度基本保持稳定。在纵向上，基部0m处的微纤丝角最大，成熟材部位微纤丝角介于16°—20°；3米高度成熟材部位微纤丝角介于12°—18°；6米与9米高度微纤丝角的差异不明显，成熟材部位微纤丝角介于10°—15°。幼龄材和成熟材部位晚材微纤丝角均小于早材处，其中幼龄材生长轮内早晚材的微纤丝角差异较大，可达10°；成熟材部位差异较小，仅有1°—3°。(3)零距拉伸技术可以迅速评价木材细胞的力学性能，可操作性强。对于人工林马尾松，零距拉伸试样的最佳厚度是80μm，最适宜的夹紧力为70psi。马尾松早材管胞的纵向抗拉强度介于316MPa—767MPa，平均548MPa，径向变化总体是从髓心向外逐渐增大，基部径向变异规律不明显；高度方向的变异是从树木基部向上逐渐增加。管胞的纵向抗拉强度随着角度的变化而变化，在0-15°之间，微纤丝角对纵向抗拉强度的影响较小；在15°-30°之间，管胞的纵向抗拉强度随角度的增大呈直线下降。(4)马尾松管胞细胞壁的弹性模量和硬度在壁厚方向不均匀，次生壁弹性模量显著大于复合胞间层；次生壁的硬度也略大。成熟材管胞次生壁的弹性模量和硬度均大于幼龄材，其中弹性模量大40％、硬度大13％；微纤丝角对细胞壁纵向弹性模量的影响程度大于对硬度的影响；次生壁和复合胞间层的弹性模量和硬度之间均存在显著的正线性相关。更多还原

【Abstract】 The remarkable mechanical properties of multicellular biomaterials reside in their complex hierarchical architecture and in specific molecular mechanistic phenomena. Mechanical behaviors of wood are defined by the morphology and mechanical properties of wood tracheids and their bonding medium. Exploring the mechanical behavior underlying the single tracheid, and building the model of multi-tracheids, make them the most important influence at the tracheid level and molecular level. It is urgent to make further investigation of the morphology and mechanical properties of wood tracheids.Softwoods are usually treat as the model material for theirs simple microstructure. In this thesis, in order to explain the relationships between structure and tracheid mechanical properties, X-ray diffraction, Zero-span tensile test and nanoindentor were used to investigate the microfibril angle, longitudinal tensile strength, cell wall modulus of elasity and cell wall hardness, respectively. The main research results were sumerized as following:（1） From pith to 8th growth ring, the radial variation patterns of tracheid length are increasing rapidly. Between 8th and 14th growth ring, tracheids length changed annomally and reach the max values. After 14th growth ring, tracheids length decrease slightly. In sum, the distribution of tracheids length of Masson Pine is nomal. And 60% tracheids length of juvenilewood distribute between 2500μm and 4000μm, 70% tracheids length of maturewood distribute between 4000μm and 5500μm. From pith outward, the tracheid width is increasing gradually, at 7th growth ring reach constant value. The average value of maturewood tracheid width at 3 meter height is 45μm, 50μm at 6 meter height, 55μm at 9 meter height.From pith to 8th growth ring, the ratio of tracheid length to tracheid width is increasing rapidly, the min value emerge at corewood, which is 55. After 14th growth ring, tracheids length change slightly, and the mean value is 80-100. The tangential diameter almost at constant intr-ring, the value is between 40μm and 45μm. Radial diameter of earlywood is 60μm, while 20μm of latewood. Thickness of double cell wall is 5μm of earlywood, while 15μm of latewood.（2） The method we have proposed using X-ray diffraction has been shown to be capable of yielding microfibril angle values. By the peak-fitting method we can determine the shape of the microfibril angle distribution. Results indicate that the microfibril angle is 20°-35°in heartwood at any height. From pith to 8th growth ring, the microfibril angle is increasing linearly. Between 8th and 14th growth ring, microfibril angle changed annomally. After 14th growth ring, the tracheid length mainly maintains constant value. In longitudinal dirction, the microfibril angle reaches max value at 0 meter height, and averge value is 16°-20°in maturewood. At 3 meter height, the averge value is 12°-18°in maturewood. There is no significant diffence between 6 and 9 meters, the averge value is 10°-15°in maturewood. No matter of maturewood and juvenilewood, the microfibril angle in earlywood is bigger than latewood. The differences are about 10°in jucenilewood, while only 1°-3°in maturewood.（3） The zero-span tension technique was used to estimate rapidly the longitudinal tensile strength of tracheids of Masson pine plantation wood. It was found optimum thickness of samples and clamping pressure for zero-span tension was 80μm and 70 psi respectively. Statistical analyses indicated stable increase of tracheids tensile strength from bark to pith, while no significant variation was observed along tree height from 6 m to 9 m. Therefore, it was inferred that zero-span tension could be used as a novel and reliable method for assessing the logitudinal tensile strength of softwood tracheids.（4） In situ imaging nanoindentation was used to characterize the differences in longitudinal modulus of elasticity and hardness of different cell wall layers of softwood tracheids, It was found that the distribution of longitudinal modulus of elasticity and hardness along cell wall thickness was uneven with much lower values at the interface between S₃ layer and cell cavity as well as SK layer and compound middle lamella compared with that measured in S₂ layer. There also existed differences in modulus of elasticity and hardness between S₂ layers of adjacent tracheids. Both modulus of elasticity and hardness of mature wood trachedis were larger than that of juvenile wood. The sapwood of mature wood tracheids displayed a modulus of elasticity nearly 1.4 times of that of juvenile wood, but only 13% harder than juvenile wood. A positive linear correlation between modulus of elasticity and hardness was also found both for sapwood and compound middle lamella of tracheids.更多还原