三维打印贝壳仿生结构的力学性能研究

发布时间：2018-05-25 13:35

本文选题：三维打印 + 仿生复合材料　；参考：《中国科学技术大学》2015年硕士论文

【摘要】：在自然界中,许多生物复合材料都具有精确的微结构和不可思议的力学性能。贝壳珍珠层正是由于其独特的碳酸钙与有机质交替的多级“砖——泥”结构以及高强度、高韧性的力学特性被研究人员广泛关注。贝壳珍珠层作为仿生复合材料的热点问题,研究其高度有序的微观结构和增韧机理对许多应用领域具有指导意义。与复合材料领域的贝壳珍珠层研究相似,三维打印也是快速成型领域的热门技术。随着三维打印技术的快速发展,研究和开发人员能够通过三维打印技术将灵感方便快捷地变成现实。本文受天然贝壳珍珠层高强度、高韧性的启发,利用三维打印技术制备仿生复合材料,结合复合材料力学剪切迟滞理论、拉伸试验、有限元分析和粗粒化相变模拟研究复合材料几何结构与整体弹性模量、断裂模式和断裂韧性的关系。我们首先根据复合材料细观力学中短纤维复合材料单元的应力传递机制推导了Cox经典剪切迟滞理方程。为了符合贝壳珍珠的天然结构,在经典剪切迟滞理论基础上,我们又引入了Begley带有砖块端部软胶层粘结作用的二维贝壳仿生单元模型,该模型能够用于描述仿生复合材料单元内部的应力分布、弹性模量和三种不同的断裂模式。随后,我们利用朗道连续相变自由能理论和Muller的双稳定性理论理解拉伸曲线的水平波动阶段。在本文的实验部分,我们根据贝壳珍珠层的天然结构制备不同几何尺寸的“砖——泥”结构复合材料拉伸试样和裂纹扩展试样。通过拉伸试验,我们详细地观察了拉伸试样在三个主要拉伸阶段内的受力形变形状态。通过改变拉伸试样的几何参数,我们获得了拉伸试样的三种最终破坏模式、拉伸试样弹性模量、几何尺寸对整体力学特性的影响趋势、带预制裂口拉伸试样的裂纹扩展特性等。本文的模拟工作主要分为三个部分,第一部分是利用有限元方法分析周期性的仿贝壳单元的应力分布,得到弹性模量与微结构尺寸之间的影响关系,分析了仿生复合结构的三种断裂模式,预测了砖块端部软胶的裂纹形核区域。第二部分是利用有限元方法进行了仿贝壳整体模型的拉伸模拟,得到了仿贝壳结构整体从外到内逐渐开裂的破坏机制。第三部分是采用双稳定性理论建立粗粒化模型,详细探讨了仿贝壳整体拉伸曲线的水平波动机制。总之,本文探索了利用立体光固化成型三维打印技术制备并研究仿生复合材料的科研模式,研究了仿贝壳复合材料的料弹性模量、断裂模式和断裂韧性,对于复合材料的结构设计具有借鉴意义。
[Abstract]:In nature, many biological composites have precise microstructures and unimaginable mechanical properties. The shell pearl layer is due to its unique multi-stage "brick - mud" structure alternating with organic matter and high strength. The mechanical properties of high toughness are widely paid attention to by the researchers. The shell pearl layer is a biomimetic composite. The hot issues of materials, studying their highly ordered microstructure and toughening mechanisms are of guiding significance to many applications.
Similar to the study of shell nacre in the field of composite materials, three-dimensional printing is also a hot technology in the field of rapid prototyping. With the rapid development of 3D printing technology, the researchers and developers can turn the inspiration into reality conveniently and quickly through three-dimensional printing technology. This paper is inspired by the high strength and high toughness of natural shell pearls. The bionic composite material was prepared by three-dimensional printing technology. The relationship between the geometrical structure of the composite and the overall elastic modulus, the fracture mode and the fracture toughness was studied with the mechanical shear lag theory, the tensile test, the finite element analysis and the coarse-grained phase transition simulation.
According to the stress transfer mechanism of the short fiber composite element in the micromechanics of composite materials, we derive the classical Cox shear hysteresis equation. In order to conform to the natural structure of shell pearls, we introduce a two-dimensional shell biomimetic sheet with the binding action of Begley with the end of the brick end soft layer on the basis of the classical shear lag theory. The model can be used to describe the stress distribution, modulus of elasticity and three different fracture modes in the bionic composite element. Then, we use Landau's theory of continuous phase transition free energy and the double stability theory of Muller to understand the stage of the horizontal fluctuation of the tensile curve.
In the experimental part of this article, we prepare the tensile specimens and crack propagation specimens of "brick mud" composite materials with different geometric sizes based on the natural structure of the shell nacre. Through the tensile test, we observe the deformation state of the tensile specimen in three main stretching stages in detail. By changing the tensile specimen, the tensile specimen is changed. The three ultimate failure modes of the tensile specimen, the elastic modulus of the tensile specimen, the influence trend of the geometric size to the overall mechanical properties, and the crack propagation characteristics of the prefabricated crack tensile specimens are obtained.
The simulation work of this paper is divided into three parts. In the first part, the finite element method is used to analyze the stress distribution of the periodic shell element, and the relationship between the elastic modulus and the microstructural size is obtained. Three kinds of fracture modes of the bionic composite structure are analyzed, and the crack nucleation area of the soft rubber at the end of the brick is predicted. Second parts are predicted. The finite element method is used to simulate the tensile model of the shell integral model, and the failure mechanism of the shell structure to crack gradually from outside to inside is obtained. The third part is a coarse grain model based on the double stability theory, and the water flat wave mechanism of the whole drawing curve of the shell is discussed in detail.
In conclusion, this paper explored the research mode of preparing and studying the biomimetic composite materials by three-dimensional printing technology, and studied the modulus of elasticity, fracture mode and fracture toughness of the shell composite material, which is of reference to the structure design of the composite.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB391

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