【作者】 黄艳辉；

【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， 2010， 博士

【摘要】 作为材料的组成物质或增强相,天然竹纤维本身的力学特性和变异程度却很少为人所知。作者以毛竹(Phyllostachys edulis)纤维细胞为主要研究对象,使用纳米压痕技术、单纤维拉伸技术、纤维束拉伸技术和传统的力学测试,首次从亚细胞水平、细胞水平、组织水平到宏观各个尺度,系统研究了毛竹纤维细胞的纵向力学性质,分析了影响力学性质的各种因素,重点考虑竹龄对毛竹纤维细胞力学性能的影响,并首次将毛竹纤维和马尾松(Pinus massoniana)木材纤维的细胞及细胞壁力学特性进行对比,以便揭示竹材结构设计和优良力学性能的本质,从而更加科学、合理的选择竹纤维原料,设计开发出高性能、高附加值的产品,促进生产工艺的不断更新,同时,也为竹材品质的基因改良和定向培育提供量化的目标和指标,丰富和推动我国木材科学理论体系的发展,具有非常重要的理论和实际意义。论文的主要研究结果如下:1.亚细胞水平上毛竹纤维的纵向力学性质(1)应用纳米压痕技术的研究结果表明,微管束不同位置处,毛竹纤维细胞壁的纵向弹性模量变化不大,以21或22 GPa为中线上下波动,但是,微管束的边缘,细胞壁的纵向弹性模量相对较小,为15.61 GPa,且变化不稳定;毛竹纤维细胞壁硬度的变化范围为0.4665-0.5603 GPa,从微管束中心向外呈逐渐减小趋势。(2)1月、2月、6月(0.5年)、18月(1.5年)竹龄的毛竹纤维细胞壁的纵向弹性模量相差不大。1月龄的弹性模量平均值与18月龄的相当,达到21.51 GPa。毛竹纤维细胞壁的硬度随竹龄呈增加趋势,变化范围为0.4673-0.6022 GPa,且在0.01水平上差异显著。2.细胞水平上毛竹纤维的纵向力学性质(3)应用单纤维拉伸技术的测定结果表明,室温下气干毛竹单纤维的荷载位移曲线为近乎完美的直线,无明显的塑性屈服,呈现典型的脆性断裂,断口形貌分为多级脱层断裂和近齐口断裂,两种模式在不同竹龄中均有分布,以多级脱层断裂为主。(4)对于0.5、1.5、2.5、4.5、6.5、8.5年竹龄的毛竹纤维,纵向抗拉强度和弹性模量在竹龄间变化不大,总体平均值分别为1543.77 MPa和33.86 GPa,平均破坏应变在竹龄间的变化相对集中,在3.63%到5.74%之间,平均值为4.85%。(5)毛竹纤维细胞壁的纵向力学特性在0.5年时已经达到力学上的成熟。3.毛竹与马尾松纤维细胞及细胞壁力学性质对比(6)毛竹单纤维平均抗拉强度和弹性模量均高出马尾松单纤维一半以上,展现出良好的高强、高弹、高变形性能。毛竹单纤维的断裂应变比马尾松高,拉断后的断口形貌以多级脱层为主,而马尾松幼龄材以不规则的撕裂型断口为主,成熟材多展现平整的横向断口。毛竹纤维次生壁的弹模和硬度优于马尾松,两者的差距达到10%左右。两者力学性质的差异与微纤丝角和细胞壁结构高度相关。4.毛竹纤维束的纵向力学性质(7)毛竹纤维束的荷载位移曲线与单纤维的相似,为直线性脆性断裂。毛竹纤维束的平均抗拉强度为461.03 MPa,平均弹性模量为37.74 GPa,两者的变异系数约25%;断裂时的平均应变为1.27%。5.毛竹纤维与宏观力学性质的关系(8)毛竹宏观薄片的应力应变曲线分布较为分散,为脆性断裂。竹壁径向不同位置的力学性质差异很大,近竹青处的力学性质远远高于近竹黄处,这与毛竹纤维含量的梯度分布高度相关。近竹青处薄片的断口为沿顺纹理的纵向劈裂,竹中处的断口呈现参差不齐的劈裂特征,近竹黄处的断口为相对整齐的横向断裂。(9)宏观薄片的平均抗拉强度和弹性模量数值占纤维束数值的三分之一左右。纤维束的平均抗拉强度和破坏应变分别占纤维细胞的29.83%和26.19%,平均弹性模量基本相当。根据毛竹宏观薄片的试验数据和细观力学混合定律推算出的纤维束的抗拉强度和弹性模量分别为651.506 MPa和52.0185 GPa,其数值高于纤维束力学性质实测值,薄壁细胞基本组织的抗拉强度和弹模分别为16.956 MPa和0.8685 GPa。(10)高强的纤维或纤维束是毛竹材优良的增强相,薄壁细胞组成的基本组织能够很好的吸收、传递、均布荷载,两者共同作用使毛竹力学特性优良,为设计绝妙的天然纤维基复合材料。更多还原

【Abstract】 As the constitute substance or reinforcement of materials, the mechanical properties and variation of natural bamboo fibers are known little. In this study, the nanoindentation technique, the single fiber tension technique , the fiber bundle tension technique and conventional mechanical test were used to study systemly the mechanical properties of fibers of Moso bamboo (Phyllostachys edulis) at the subcellular, cell, tissue and macroscopic scale for the first time. The various factors affecting the mechanical properties were analysed. The influence of age factor on the mechanical properties of bamboo fiber was emphatically considered. The mechanical properties of fiber cell wall and single fiber of Moso bamboo and Masson pine (Pinus massoniana) were compared firstly. In order to reveal the structure design and excellent mechanical properties of bamboo, so as to choose bamboo fibers more scientifically and rationally, to design and develop the products with high properties and high value-added, to promote the continuous update of production process. Meanwhile, that would provide quantifiable objective and indexes for the gene modified and oriented cultivation of bamboo, enriching and improving the development of wood science of China, and would be very important for the theoretics and practice.The main research results were as follows:1. The longitudinal mechanical properties of fibers of Moso bamboo on the cell wall level(1)The study results of using nanoindentation showed that, in different positions of the vascular bundle, the longitudinal modulus of elasticity of cell wall of bamboo fiber were similar, the value were fluctuated at the middle line of 21 or 22 GPa. However, near the edge of the vascular bundle, the longitudinal modulus of elasticity of cell wall were relative small, which was about 15.61 GPa, and the values were very instable. The range of hardness of cell wall of bamboo fiber was from 0.4665 to 0.5603 GPa, and the measurement results showed a decreasing tendency from the center to edge of the vascular bundle.(2) The longitudinal modulus of elasticity of cell wall were comparable in value for the bamboo fibers with the age of 1, 2, 6 and 8 months. For the 1 month cell wall, the average value of modulus of elasticity reached to 21.51 GPa, which corresponded to those of 18 months. An increasing trend of cell wall hardness were found with different age, and the value ranged from 0.4673 to 0.6022 GPa, and the difference was significant at 0.01 level.2. The longitudinal mechanical properties of fibers of Moso bamboo on the cell level(3)Single fiber tension test proved that the load-displacement curves of air dried bamboo single fiber were nearly perfect line at room temperature, which had no significant yield and slippage, presenting a typical brittle fracture. The fracture surfaces of single fibers were divided into multilevel off-layer fracture and transverse break. The two kinds of fracture were all be found among different age, but the former were more ordinary.(4)For the bamboo fibers of 0.5, 1.5, 2.5, 4.5, 6.5, 8.5 years old, the tensile strength and modulus of elasticity of longitudinal changed little, the average values of which were 1543.77 MPa and 33.86 GPa, respectively, and the average break strain changed very small, between 3.63% and 5.74%, with an average value of 4.85%.(5)The longitudinal mechanical properties of cell wall of bamboo fibers achieved to optimization in the years old of 6 months.3. Comparetion of mechanical properties of fiber cell and cell wall of Moso bamboo and Masson pine(6)The average tensile strength and modulus of elasticity of bamboo single fibers were one and a half bigger than that of Masson pine single fibers. The bamboo fibers showed better strength, higher elasticity and bigger deformation performance. The break strain of bamboo fibers were bigger than those of pine, and the multilevel off-layer fracture were conmmon in bamboo fibers, however, for pine, irregular brush fracture was usually found in the juvenile wood, and transverse fracture was usually found in the mature wood. The modulus of elasticity and hardness of secondary cell wall of bamboo fibers were superior to those of pine fibers, the difference between them reached to 10%. The differences of mechanical properties between them were correlated highly to the microfibril angle and cell wall structure.4. The longitudinal mechanical properties of fiber bundles of Moso bamboo(7)The load-displacement curves of fiber bundles were similar to those of single fibers, all of them were linear brittle fracture. For bamboo fiber bundles, the average tensile strength was 461.03 MPa, the average modulus of elasticity was 37.74 GPa, both coefficient variation of them were all about 25%, the the average break strain was 1.27%.5. Correlation of bamboo fibers and the macroscopic mechanical properties(8)The distribution of stress-strain curves of thin slices were very scattered, and the fracture was brittle. On radial direction of bamboo, the mechanical properties was different, which was biggest in the outer part of bamboo, this difference were highly correlated with the gradient distribution of bamboo fibers content. In the outer part of bamboo, the fracture of thin slices was longitudinal splittary, in the middle part, the fracture showed uneven splitting feature, in the inner part, the fracture presented relative smooth, transverse feature.(9)The average tensile strength and modulus of elasticity of thin slices accounted for about one third of fiber bundles. The average tensile strength and break strain of fiber bundles were about 26.19% and 29.83% of fibers, respectively, while the average modulus of elasticity were roughly equal. According to the tested data of thin slices and the mixed law, the calculated tensile strength and modulus of elasticity of fiber bundles were 651.506 MPa and 52.0185 GPa, respectively, both of them were higher than the tested value, and 16.956 MPa and 0.8685 GPa for parenchyma.(10)The fibers or fiber bundles with high strength are the better reinforcement substance for bamboo, and the ground tissue constituted by parenchyma can absorb, transmit, uniform load, both of them make the mechanical properties of bamboo excellent. Bamboo is natural fiber composites of excellent designed.更多还原