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1、基于显微CT技术的泡沫铜基本性能有限元预测方法研究Finite Element Analysisfor the Basic Performance of Copper FoamBased on Micro-Computed Tomography 一级学科： 材料科学与工程 学科专业： 材 料 学 作者姓名： 指导老师： 20XX年12月中文摘要中文摘要本文以航空发动机对离心通风器轻质、紧凑、高效的需求为背景，以10PPI聚氨酯海绵为基体，采用超声波辅助电沉积工艺制备泡沫铜材料。通过对泡沫铜孔结构进行三维重构，建立了与电沉积泡沫铜的真实三维结构相一致的有限元简化模型十四面体三棱柱模型。基于十四面
2、体三棱柱模型，开展了对泡沫铜基本性能、渗流和对流换热性能的有限元计算方法研究，深入研究了十四面体三棱柱单胞模型对各项性能的影响，建立了孔结构参数与各项性能之间的定量关系，并对模型进行优化设计。采用显微CT对泡沫铜试样进行断层扫描，得到一系列泡沫铜试样的二维断层图像。对图片进行阈值分割处理，通过Origin软件计算出一定阈值下泡沫铜试样的孔隙率，并由排水法测得试样的孔隙率，对比孔隙率的计算值和测试值，确定最终的试样阈值。基于泡沫铜的显微CT断层扫描结果，对泡沫铜孔结构进行三维重构，泡沫铜孔洞分布均匀，孔的三维结构近似为十四面体。利用ANSYS软件的前处理模块，以十四面体为基体，建立泡沫铜有限元简
3、化模型十四面体三棱柱模型，该模型较好地反映了泡沫铜的三维结构特征。基于胡克定律对泡沫铜试样进行单轴压缩屈服强度测试，并利用ANSYS有限元软件对泡沫铜屈服强度进行有限元模拟。根据上端面应力变化和位移变化，得出应力应变曲线，进一步计算出泡沫铜的屈服强度。泡沫铜在单轴应力作用下的应力应变曲线数值模拟结果和试验测试结果有着良好的一致性。由于十四面体具有高度的对称性，泡沫铜的等效应力整体分布较为均匀，棱相交的地方由于形状的突变导致应力较为集中，随着应力的增加该区域将优先发生塑形变形；峰值应力主要集中在泡沫铜棱相交的区域，塑形变形从该区域开始逐渐向四周扩展，当载荷超出泡沫铜承载极限时，失效发生。随泡沫铜
4、的孔隙率增加，其屈服强度呈指数幂减小。基于傅里叶热传导方程对泡沫铜的有效热导率进行试验测定，并利用ANSYS有限元软件对泡沫铜的有效热导率进行有限元模拟。泡沫铜的有效热导率的有限元计算结果和试验测试结果有着良好的一致性。由于泡沫铜的多孔结构，热流密度在模型上的分布不均匀，泡沫铜棱相交处热流密度最大，更易产生热应力集中，失效易于从此处发生。泡沫铜的有效热导率基本不随孔密度规格的变化而变化。随着泡沫铜孔隙率的增大，其孔棱横截面积减小，有效热导率随之降低。基于Forchheimer-extend-Darcy定律对泡沫铜式样的渗流和对流换热性能进行测试，并利用Fluent软件对泡沫铜渗流和对流换热性能
5、进行有限元计算。泡沫铜渗流和对流换热性能的有限元计算结果和试验测试结果有着良好的一致性。泡沫铜的渗流性能随着孔隙率减小而降低。低孔密度、高孔隙率的泡沫铜的渗透性能较好。对流换热系数随孔密度增加而变大，随孔隙率的提高而减小。在高孔隙率条件下，泡沫铜骨架内的固相热传导过程对孔隙率的变化较为敏感，当孔隙率减小、即表观密度增加时，固相热传导的作用明显增强，从而有利于对流换热能力提高。增大流速、提高泡沫金属孔密度，均可增强泡沫金属的对流换热性能。对泡沫铜孔结构进行主动优化设计，得到泡沫铜十四面体圆柱棱模型。对相同孔结构参数的泡沫铜十四面体圆柱棱模型进行有限元分析。相同孔隙率和孔密度条件下，泡沫铜十四面体
6、圆柱棱模型的压缩屈服强度和有效热导率较高，渗流和对流换热性能与十四面体三棱柱模型相比也更为优异。即十四面体圆柱棱结构泡沫铜单胞模型最优结构。关键词：泡沫铜，显微CT技术，有限元计算，屈服强度，有效热导率，渗流性能，对流换热性能，结构优化iiABSTRACTABSTRACTAeroengine centrifugal ventilator is developing toward lightweight, compact and high-performance. 10 PPI polyurethane sponge is used as the matrix and copper foam i
7、s prepared by electro deposition process with ultrasonic. Three-dimensional structure of copper foam is reconstructed，and furthermore, the tetrakaidecahedron tri-prism model as the simplified finite element model of copper foam is established by using the ANSYS finite element analysis software, whic
8、h can reflect the structure of copper foam more truly. On the basis, the yield strength, the effective thermal conductivity, the permeability and the convective heat transfer of copper foam are calculated by finite element method based on ANSYS. In the meanwhile, the relationship between the propert
9、ies and the single cell model of copper foam is studied and quantitative relations between pore structure parameters and properties of the copper foam are established. In addition, the tetrakaidecahedron tri-prism model is optimized.The copper foam specimens are scanned using the Micro CT and a set
10、of 2D tomography images are obtained. Image segmentation is processed in MATLAB, the porosity of copper foam with a certain threshold is calculated by Origin software. Comparing with the porosity measured by drainage method, the final threshold value of specimens is determined. On the basis, the 3D
11、structure of copper foam is reconstructed. It can be observed that the internal spatial structure of copper foam is regular with its holes evenly distributed and isotropic, the 3D structure of pore in the copper foam is approximately tetrakaidecahedron while the 2D structures are roughly quadrilater
12、al and hexagonal. The tetrakaidecahedron tri-prism model is proposed by the pretreatment module of ANSYS software, which can truly reflect the structure of copper foam.Based on the Hookes law, Uniaxial compression yield strength of copper foam samples are tested, and the ANSYS finite element analysi
13、s software is used in numerical simulation for the compressive yield strength of copper foam. According to the change of stress and displacement of the top surface, the stress-strain curve is drawn and the yield strength of copper foam is calculated in addition. Both stress-strain curves of numerica
14、l simulation and experimental testing under uniaxial stress with copper foam show a good consistency under uniaxial stress load. Because of the high symmetry of tetrakaidecahedron, the equivalent stress distribution of foam copper is relatively uniform. While the peak of stress is mainly concentrate
15、d in the area where the foam copper edges intersect for the mutation of the structure，where the plastic deformation expanded around from the region, the plastic deformation may occur preferentially when the stress increase. And then the structural failure occurred when the load exceeds the bearing l
16、imit of foam copper. With increasing of the porosity of foam copper, the yield strength decreases exponentially.Based on the Fourier heat conduction equation, the effective thermal conductivity of copper foam is texted, and the ANSYS finite element analysis software is used in numerical simulation for t
