發(fā)布時間：2018-08-04 11:29

【摘要】：隨著納米科技的飛速發(fā)展，對微納米零件的需求越來越多，同時對其使用性能也提出了很高的要求。受表面效應、量子效應、小尺度效應的影響，機械微結構達到微米甚至納米量級時，微構件斷裂等力學性能與常規(guī)構件表現(xiàn)出很大的差異。因此，加快建立微納米零件的加工和設計理論已成為當前制造業(yè)領域一項很重要的任務。本文借助準連續(xù)介質(zhì)方法，研究微構件在不同加載下的斷裂特性，這對微構件的力學性能等具有重要的理論價值和現(xiàn)實意義。論文研究工作如下： 首先，搭建了準連續(xù)介質(zhì)仿真平臺，建立拉伸過程的多尺度仿真模型，并通過計算分析了模型的有效性。 其次，模擬并分析了單晶銅懸臂梁彎曲過程的尺寸效應及梁彎曲失效原因。研究了梁厚度、跨厚比及晶向設置對兩端固支梁彈性模量等的影響，利用位錯及滑移理論分析了三種不同晶向設置兩端固支梁模型的微觀變形機理。結果發(fā)現(xiàn)，連續(xù)介質(zhì)理論及其衍生理論對微/納構件已不再適用。懸臂梁的厚度對力學性能影響很大。兩端固支梁的彈性變形階段的彈性模量隨應變的增加而增大，梁的尺寸越小彈性模量增加越快。相同跨厚比下，梁的初始彈性模量是定值，受尺寸效應、表面效應影響不明顯。梁的初始彈性模量、最大撓度、彎曲強度等特性隨梁厚的增大而減小。 最后，建立了單晶銅納米桿的壓縮過程多尺度仿真模型，研究了結構尺寸參數(shù)對納米桿壓縮力學性能的影響，通過分析納米桿在壓縮變形時的形變、內(nèi)部應力和應變能的演化規(guī)律，獲得了納米桿壓縮變形及潰裂機制。分析了納米桿在不同壓縮條件下的彈性模量、彈性極限、屈服極限及泊松比等力學特性。結果表明：與宏觀值相比，單晶銅納米桿壓縮時的彈性模量、彈性極限和屈服極限表現(xiàn)出明顯的尺寸效應，而其泊松比的尺寸效應并不明顯；納米構件一維方向尺寸的變化對其力學性能影響不大。
[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 The results show that the continuum theory and its derivation theory are no longer applicable to micro / nano components.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.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2012
【分類號】：TH114

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本文編號：2163846