基于跨尺度模拟的机械微结构断裂行为研究

发布时间：2018-08-04 11:29

【摘要】：随着纳米科技的飞速发展，对微纳米零件的需求越来越多，同时对其使用性能也提出了很高的要求。受表面效应、量子效应、小尺度效应的影响，机械微结构达到微米甚至纳米量级时，微构件断裂等力学性能与常规构件表现出很大的差异。因此，加快建立微纳米零件的加工和设计理论已成为当前制造业领域一项很重要的任务。本文借助准连续介质方法，研究微构件在不同加载下的断裂特性，这对微构件的力学性能等具有重要的理论价值和现实意义。论文研究工作如下：首先，搭建了准连续介质仿真平台，建立拉伸过程的多尺度仿真模型，并通过计算分析了模型的有效性。其次，模拟并分析了单晶铜悬臂梁弯曲过程的尺寸效应及梁弯曲失效原因。研究了梁厚度、跨厚比及晶向设置对两端固支梁弹性模量等的影响，利用位错及滑移理论分析了三种不同晶向设置两端固支梁模型的微观变形机理。结果发现，连续介质理论及其衍生理论对微/纳构件已不再适用。悬臂梁的厚度对力学性能影响很大。两端固支梁的弹性变形阶段的弹性模量随应变的增加而增大，梁的尺寸越小弹性模量增加越快。相同跨厚比下，梁的初始弹性模量是定值，受尺寸效应、表面效应影响不明显。梁的初始弹性模量、最大挠度、弯曲强度等特性随梁厚的增大而减小。最后，建立了单晶铜纳米杆的压缩过程多尺度仿真模型，研究了结构尺寸参数对纳米杆压缩力学性能的影响，通过分析纳米杆在压缩变形时的形变、内部应力和应变能的演化规律，获得了纳米杆压缩变形及溃裂机制。分析了纳米杆在不同压缩条件下的弹性模量、弹性极限、屈服极限及泊松比等力学特性。结果表明：与宏观值相比，单晶铜纳米杆压缩时的弹性模量、弹性极限和屈服极限表现出明显的尺寸效应，而其泊松比的尺寸效应并不明显；纳米构件一维方向尺寸的变化对其力学性能影响不大。
[Abstract]:With the rapid development of nanotechnology, there are more and more demands on micro and nano parts. Under the influence of surface effect, quantum effect and small scale effect, when the mechanical microstructure reaches the order of micron or nanometer, the mechanical properties such as fracture of microstructures are very different from those of conventional members. Therefore, it has become an important task in the field of manufacturing industry to accelerate the establishment of the theory of machining and design of micro-and nano-parts. In this paper, the fracture characteristics of microstructures under different loading conditions are studied by means of quasi-continuum medium method, which is of great theoretical and practical significance to the mechanical properties of microstructures. The research work is as follows: firstly, the quasi-continuum medium simulation platform is built, and the multi-scale simulation model of stretching process is established, and the validity of the model is analyzed by calculation. Secondly, the size effect of single crystal copper cantilever beam during bending and the failure reason of beam bending are simulated and analyzed. The effects of beam thickness, span thickness ratio and crystal orientation on the elastic modulus of two end clamped beams are studied. The microscopic deformation mechanism of three kinds of fixed beam models with different crystal directions is analyzed by using dislocation and slip theory. The results show that the continuum theory and its derivation theory are no longer applicable to micro / nano components. The thickness of cantilever beam has great influence on mechanical properties. The elastic modulus increases with the increase of the strain, and the smaller the size of the beam, the faster the elastic modulus increases. At the same span thickness ratio, the initial elastic modulus of the beam is constant, but the influence of the surface effect is not obvious due to the size effect. The initial elastic modulus, maximum deflection and bending strength of the beam decrease with the increase of the beam thickness. Finally, a multi-scale simulation model of the compression process of single crystal copper nanorods is established, and the effect of structural dimension parameters on the compressive mechanical properties of nanorods is studied. The deformation of nanorods during compression deformation is analyzed. The mechanism of compressive deformation and cracking of nanorods was obtained by the evolution of internal stress and strain energy. The elastic modulus, elastic limit, yield limit and Poisson's ratio of nanorods under different compression conditions were analyzed. The results show that compared with macroscopic values, the elastic modulus, elastic limit and yield limit of single crystal copper nanorods show obvious size effect, but the size effect of Poisson's ratio is not obvious. The change of one-dimensional dimension has little effect on the mechanical properties of nanostructures.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TH114

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