生物复合材料的屈曲和断裂行为研究

发布时间：2018-07-05 18:03

本文选题：生物复合材料 + 纳米结构　；参考：《北京理工大学》2015年硕士论文

【摘要】：骨骼、牙齿和贝壳等生物材料是多级纳米复合材料，具有优异的力学性能。在纳米尺度上矿物质晶体错列镶嵌在柔软的蛋白质基质中，矿物质晶体具有很大的长细比。本文第一部分通过基于梁-弹簧模型的有限元研究大尺寸交错结构的屈曲行为。用Euler梁模拟矿物质晶体，并用一系列分布弹簧去等效蛋白质基质，考虑间断交错模型、铰接交错模型和连续梁模型三种情况。当长细比较短时，间断模型中矿物质梁端部自由，更容易失稳，主要发生类似刚体旋转的形式，几乎没有弯曲，蛋白质部分既有剪切又有侧向拉压变形，模型呈现周期的局部屈曲模式；铰接模型中矿物质梁在铰接约束作用下，抗屈曲能力较强，不易传递屈曲波形，在加载边界附近区域呈局部屈曲模式。长细比增大后，矿物质容易弯曲但不易整体转动，两种交错模型的屈曲模态变得一致并接近连续模型的剪切屈曲模式，，临界载荷结果验证了我们模态的分析结果，并且得出增大矿物质长细比可提高生物材料的屈曲强度的结论。第二部分研究基于铰接模型的生物材料的屈曲问题，讨论了矿物质晶体对齐排布和交错排布两种情况。发现矿物质晶体对齐排布时，屈曲强度最低；而对称交错排布时，屈曲强度最高；增大矿物质的长细比或体积分数均能提高屈曲强度，并趋于连续矿物质模型的屈曲强度。由此得出，不论是间断模型还是铰接模型，通过交错排布同时增加矿物质长细比，可提高材料的抗屈曲能力并接近完美连续结构，这对结构稳定性起到至关重要的作用。第三部分讨论含有裂纹的交错结构的断裂行为，当矿物质增强相排布方向与裂纹平行时，增强相对裂纹尖端的应力集中现象不起作用，二者垂直时，能明显降低裂纹尖端的应力强度因子；同时，越接近对称交错模式、矿物质体积分数越高，长细比越大，裂纹尖端的应力强度因子越低。
[Abstract]:Biomaterials such as bone, teeth and shells are multistage nanocomposites with excellent mechanical properties. The mineral crystals are mislaid in soft protein matrix on nanometer scale, and the mineral crystals have a large aspect ratio. In the first part of this paper, the buckling behavior of large scale staggered structures is studied by finite element method based on beam-spring model. The mineral crystals are simulated by Euler beam, and a series of distributed springs are used to degrade the equivalent protein matrix. Three kinds of cases are considered: the interlaced interleaving model, the hinged interlaced model and the continuous beam model. When the length is relatively short, the end of the mineral beam is free in the discontinuous model, and it is more prone to instability. It mainly occurs in the form of rigid body rotation, almost no bending, and the protein part has both shear and lateral tension and compression deformation. The model presents periodic local buckling mode, and the mineral beam in the hinge model has strong buckling resistance and is not easy to transmit buckling waveform under hinged constraint, and the local buckling mode is found in the region near the loading boundary. When the slenderness ratio increases, the mineral is easy to bend but not to rotate as a whole. The buckling modes of the two staggered models become consistent and close to the shear buckling mode of the continuous model. The critical load results verify the results of our modal analysis. It is concluded that increasing the aspect ratio of minerals can improve the buckling strength of biomaterials. In the second part, the buckling problem of biomaterials based on hinged model is studied, and the alignment and staggered arrangement of mineral crystals are discussed. It is found that the buckling strength is the lowest when the mineral crystals are aligned and the highest when the symmetry is staggered, and the buckling strength can be increased by increasing the aspect ratio or volume fraction of the mineral, and tends to the buckling strength of the continuous mineral model. It is concluded that both the discontinuous model and the hinged model can improve the buckling resistance of the material and approach the perfect continuous structure by staggered arrangement and increase the ratio of mineral slenderness at the same time, which plays an important role in the stability of the structure. In the third part, the fracture behavior of staggered structures with cracks is discussed. When the arrangement direction of the mineral reinforcement phase is parallel to the crack, the stress concentration phenomenon of the enhanced phase relative to the crack tip does not work. When the two phases are perpendicular to each other, The stress intensity factor at the crack tip can be obviously reduced, and the higher the mineral volume fraction and the greater the aspect ratio, the lower the stress intensity factor at the crack tip.
【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;O341

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