【作者】 王立新；

【导师】 秦庆华； 王建山；

【作者基本信息】 天津大学 ， 生物力学， 2016， 硕士

【摘要】 木材、骨头、肌腱、韧带和攀附植物卷须等生物材料在分子尺度、微观甚至宏观尺度上具有手性微结构或多级手性结构。这些天然手性生物材料中含有的螺旋或扭转微结构不仅能够“智能”地调控生物组织的形貌,而且为生物材料提供了优良的物理和力学性能。材料韧性是重要的力学性能之一。木材和骨头等生物材料的韧性来源于多级微结构的协同效应,其中由胶原纤维或纤维素纤维等形成的螺旋微结构在微观尺度上对韧性有很大的贡献。但是目前手性微结构如何提高材料的韧性还不清楚。研究手性微结构生物材料的结构-性能关系不仅有助于加深对自然界各种现象的理解,还启发我们设计和构造基于手性微结构的先进功能材料。本文基于木材裂纹扩展过程中的纤维桥联机制,利用有限元软件ABAQUS建立了螺旋纤维拔出的力学模型。通过模拟结果,研究了螺旋角度对螺旋纤维拔出过程中拉拔载荷和能量损耗的影响,分析了螺旋微结构对于生物材料失效过程的作用。同时分析了圆柱扭转纤维和扭转带纤维拔出的过程,考察了纤维与基体不同弹性模量比的影响以及拉拔过程中拉拔速度对于纤维基体“stick-slip”行为的影响。最后模拟了简单的螺旋纤维复合材料系统I型裂纹的扩展过程,研究了螺旋纤维在裂纹扩展过程中起到的增韧作用。其次,针对肌腱、韧带、攀附植物卷须等生物材料,建立了螺旋纤维复合材料系统在大变形下的轴向拉伸以及单纤维碎断的有限元模型。通过比较螺旋纤维断裂密度随拉伸应变的变化和断裂过程中能量损耗变化,分析了螺旋纤维断裂过程。并进一步分析界面强度、纤维强度等对于大变形下生物材料轴向拉伸过程的影响,初步揭示了手性微结构对生物材料韧性等力学性能的影响。更多还原

【Abstract】 Many biological materials such as wood,bone,tendon,ligament and climbing tendrils possess the wildly existed chiral microstructures or multilevel chiral structures at molecular scale,microscale and macroscale.The extensively existed helical or twisted microstructures can not only control smartly the macroscopic morphologies of plant tissues,but also provide biological materials with a wide range of superior physical and mechanical properties.Toughness is one of the most important material mechanical properties.Toughness of biological materials such as wood and bone results from synergistic effect of multilevel chiral microstructures,among which chiral microstructures made up of collagen fibers or cellulose fibers have a great contribution on the toughness at microscale.However,how these helicoid microstructures can enhance the toughness of biological materials remains an open question.Therefore,understanding and unravelling the structure-property relationships of biological materials not only can help deepen our understanding of various phenomena of nature,but also can inspire us to design and construct advanced functional materials based on chiral microstructures.In this paper,we establish helicoid fiber pullout mechanical model using finite element software ABAQUS based on fiber bridging mechanisms during crack propagation in woods.Taking advantage of simulation results,we study the influence of twist angel on pullout force and energy dissipation in helical fiber pullout process.At the same time,we analyze the pullout process of cylindrical torsion fiber and twisting belt fiber.We also investigate the influence of different elastic modulus and the effect of loading velocity on ‘stick-slip’ behavior between the fiber and matrix.Finally,we coarsely examine the effects of helical fiber on mode I crack propagation in a simple composite system to evaluate the toughening effects of helical fiber.Then,we construct helicoid fiber-matrix system finite element model of axial tension under large deformation and single fiber fragmentation based on biological materials such as tendon,ligament and climbing tendrils.We compare the helicoid fiber fracture density changing with tensile strain and energy dissipation in the process of fiber fracture.Furtherly we analyze the influence of interface strength and fiber strength on axial tensile of biological materials under large deformation,preliminary revealing that the effects of helical microstructures on mechanical properties such as toughness of biological materials.更多还原