生物复合材料的断裂行为研究

发布时间：2018-02-24 15:29

本文关键词： 生物复合材料多级结构断裂分子动力学　出处：《北京理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：贝壳、牙齿、骨骼等生物材料都是多级纳米复合材料,在纳米尺度上矿物质相交错镶嵌在柔软的蛋白质基质中。这种交错层叠的排布使得材料具备了良好的力学性能。深入研究生物材料的力学性能与其多尺度(多级)微纳米结构之间的关系,对于人工合成性能优异的仿生材料具有重要意义。本文依据生物材料的微观多级结构特性,模拟研究具有多级结构的生物复合材料的动态破坏行为和断裂机制,为人工合成高性能的仿生材料提供理论支持。本文第一部分运用分子动力学方法模拟研究了蛋白质相体积分数远大于矿物质相,且含有中心裂纹的一级结构的力学行为。通过研究发现,裂尖应力强度因子随着增强纤维长度的增大而减小,最终趋于一个稳定值;临界扩展力随着增强纤维长度的增大而增大。该结果均表明增大增强纤维的长度能够有效削弱裂尖的应力集中现象。当增强纤维的强度远大于基质时,裂纹扩展绕过增强纤维,呈现增强纤维被“拔出”的现象;当增强纤维的强度较小时,长度较小的增强纤维被“拔出”,而长度较大的增强纤维发生断裂。第二部分运用分子动力学方法模拟研究了蛋白质体积分数远小于矿物质相,且边界含预制裂纹的“类骨”多级结构的力学行为。研究发现,对于仅含一级结构的模型,矿物质长细比较小时,裂纹主要沿着蛋白质相扩展,矿物质相被“拔出”,扩展过程中呈现出明显的“桥连”现象,而“桥连”则正是生物材料的一种重要的增韧机制;随着矿物质长细比增大,裂纹直接穿过矿物质相扩展。对于含有二级结构的模型,矿物质长细比较小时,裂纹主要沿着蛋白质相扩展;随着矿物质长细比增大,裂纹扩展路径逐渐变得曲折,该过程既有蛋白质相的破坏,也有矿物质相的破坏;当长细比足够大时,有二级结构被“拔出”的现象出现,同时伴随着矿物质相的断裂。在研究中我们还找到了一组最优的结构,使得材料既能获得良好的韧性,也能具备足够的强度,这为人工合成材料提供了依据。
[Abstract]:Shells, teeth, bones and other biomaterials are multistage nanocomposites, Minerals are interlaced in soft protein substrates on a nanoscale scale. This interlaced arrangement makes the materials possess good mechanical properties. Further study on the Mechanical Properties of Biomaterials and their Multi-scale (multilevel). The relationship between microstructures and nanostructures, It is of great significance to synthesize biomimetic materials with excellent properties. According to the microcosmic and multilevel structure characteristics of biomaterials, the dynamic failure behavior and fracture mechanism of biomaterials with multilevel structures are simulated and studied in this paper. In the first part of this paper, the volume fraction of protein phase is much larger than that of mineral phase by molecular dynamics simulation. It is found that the stress intensity factor of crack tip decreases with the increase of fiber length and tends to a stable value. The results show that increasing the length of the reinforced fiber can effectively reduce the stress concentration at the crack tip. When the strength of the reinforced fiber is much greater than that of the matrix, the crack propagation bypasses the reinforced fiber. A phenomenon in which the reinforced fiber is "pulled out"; when the strength of the reinforced fiber is small, The smaller reinforced fibers were "pulled out" and the longer reinforced fibers were broken. In the second part, the molecular dynamics method was used to simulate that the protein volume fraction was much smaller than the mineral phase. And the mechanical behavior of "bone-like" multistage structures with prefabricated cracks at the boundary. It is found that for models with only primary structure, the crack propagates mainly along the protein phase when the mineral length is small. When the mineral phase is "pulled out", the phenomenon of "bridging" appears in the process of expansion, and "bridging" is an important toughening mechanism of biomaterials. The crack propagates directly through the mineral phase. For the model with secondary structure, when the mineral length is small, the crack mainly propagates along the protein phase, and with the increase of the aspect ratio of the mineral, the crack propagation path becomes more and more zigzag. In this process, both the protein phase and the mineral phase are destroyed; when the aspect ratio is large enough, the secondary structure is "pulled out". At the same time, along with the fracture of mineral phase, we also find a group of optimal structure, which makes the material can obtain good toughness and enough strength, which provides the basis for synthetic materials.
【学位授予单位】：北京理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB33

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