闭孔泡沫材料3-D几何建模及力学性能分析

为建立闭孔泡沫金属材料泡孔及其孔壁结构形状数字化模型,提出在Voronoi多面体内填充空心椭球(Hollow Ellipsoid Filled in Voronoi Cell,HEFIVC),并以椭球半轴长度及其方位角为变量、胞体质量最小为目标建立优化模型,迭代模拟闭孔泡沫金属材料中气泡的长大过程,成功构建了不同孔隙率的泡沫铝几何模型。通过拟合确定了HEFIVC模型中最小孔壁厚度与孔隙率间的关系。将具有周期性边界的闭孔泡沫材料HEFIVC几何模型导入MSC.MARC有限元软件,模拟分析了低孔隙率泡沫铝的静态压缩力学性能,通过与泡沫铝压缩实验结果对比,验证了该模型的准确性。     

基于不同材料模型的闭孔泡沫铝疲劳分析

使用真实多孔模型和三种均质材料模型(可压缩泡沫模型、等向强化模型和随动强化模型)对AlSi7闭孔泡沫铝进行疲劳分析.所用三种均质材料模型的数值分析是基于先前在应力比R=0.1的振荡拉伸载荷下进行疲劳测试所得实验结果.计算结果表明,等向强化模型和随动强化模型均适用于分析闭孔泡沫铝的疲劳行为.此外,与等向强化模型相比,随动...     

泡沫铝压缩性能模拟研究的现状与展望

力学性能研究是泡沫铝应用的基础,通过压缩性能模拟研究不仅可以预测多孔材料力学性能,还能扩展泡沫金属材料力学性能数据库。本文从微观结构力学模型和宏观数值仿真研究的角度对多孔泡沫铝力学性能研究予以综合概述。对微观模拟的各种细观结构模型进行分析和评价,认为各模型的优缺点共存,在实际操作中需综合考虑灵活运用;而宏观模拟需充分考虑其制备工艺和制造缺陷,建立一些带有微结构缺陷的模型代表真实泡沫铝来测试其压缩性能。无论是微观模型还是宏观模型都不能完全描述目前制备的开孔和闭孔泡沫铝材料,模拟结果与试验结果有些会出入很大,需累积大量数据以发现准确的规律。     

闭孔泡沫铝在压剪加载下的双向力学行为（英文）

为了研究闭孔泡沫铝合金在双轴加载下的屈服行为,对一种闭孔泡沫铝在较宽的加载角度范围开展压剪复合加载试验和数值模拟研究。压剪复合加载通过加入一对斜端面垫块和一个长方体套筒来实现。测试屈服面,并与多个理论模型推导得到的屈服面进行比较。通过将闭孔泡沫铝的多孔结构建模成十四面体,对其双轴加载行为进行有限元模拟。结果表明,在压剪复合加载试验条件下,闭孔泡沫铝的屈服从试件应力集中的角上开始,而且试样/垫块接触面的应力分布不再均匀。在所研究的加载角度范围内,胞元尺寸越大,屈服应力越大。泡沫铝合金的密度相对于孔径尺寸来说是影响其力学行为的主导因素,因而在工程应用中也显得更加重要。     

基于真实结构的多孔铝缓冲吸能研究

基于真实结构的多孔铝材料，提出了随机胞孔投放算法与材料属性识别算法，并根据结构特点建立了具有随机胞孔大小、随机胞孔分布及随机壁厚的数值计算模型。利用现有实验数据对数值计算模型进行了准静态压缩及动态压缩验证，然后分析了冲击速度、胞孔随机分布、均匀壁厚和随机壁厚对闭孔多孔铝材料缓冲吸能的影响。结果表明，所建立三维细观模型在准静态及动态压缩下的结果与实验数据趋势一致，在准静态下空气对闭孔多孔铝的力学性能影响可忽略。闭孔多孔铝的缓冲吸能能力受冲击速度和壁厚的影响较明显，受胞孔随机分布的影响很小。     

泡沫金属的尺寸效应和约束条件下的压缩性能

通过准静态单轴压缩和径向约束轴向压缩实验,研究了闭孔泡沫铝的尺寸效应,分析了试件尺寸(直径和高度)和密度对泡沫材料力学性能的影响。结果表明：单轴压缩时闭孔泡沫铝力学性能具有较为明显的尺寸效应,而径向约束轴向压缩时闭孔泡沫铝的尺寸效应不明显。两种加载情况下,密度都对闭孔泡沫铝的力学性能有着明显的影响。与单轴压缩相比,径向约束轴向压缩时闭孔泡沫铝的屈服应力和平台应力随密度的变化更为显著。     

Al基和Al-6Si基闭孔泡沫铝的动态吸能性能

利用熔体转移发泡法制备不同基体成分不同密度的闭孔泡沫铝,从能最吸收能力、能量吸收效率以及能量吸收图等方面对其动态吸能性能进行研究.结果显示:无论是Al基还是Al-6Si基的闭孔泡沫铝,能量吸收能力随应变的增加而增大,且随相对密度的增加,能量吸收能力先增加后减小;能量吸收效率的变化具有明显的缓慢增加、趋于平缓和缓慢减小的特征;随着应力的增加,闭孔泡沫铝单位体积的吸能能力先快速提高,达到一定值后上升趋势减缓,出现明显的肩;对应此密度的闭孔泡沫铝可以提供最大容许应力σp,且随着相对密度的减小,最大容许应力σp逐渐减小;相同密度Al基和Al-6Si基的闭孔泡沫铝能量吸收能力相比,前者的要大一些,但Al-6Si基闭孔泡沫铝的吸能效率要比Al基闭孔泡沫铝的吸能效率高,且最高吸能效率比较稳定持久.     

搅拌摩擦加工制备的闭孔泡沫铝的组织及性能

为避免传统方法制备大面积闭孔泡沫铝工艺过程的局限性，采用搅拌摩擦加工技术结合加热工艺制备闭孔泡沫铝复合材料。采用有限元软件对搅拌摩擦加工制备预制体过程的温度场进行了模拟仿真，研究了制备工艺参数对泡沫铝预制体质量的影响规律。利用光学金相显微镜对不同加工工艺参数及发泡时间条件下制备的泡沫铝孔隙率和形貌进行了分析。同时，对闭孔泡沫铝进行了准静态压缩性能试验，研究了不同孔隙率下泡沫铝的压缩性能。结果表明，与搅拌针移动速度相比，不同旋转速度对闭孔泡沫铝预制体的形貌影响更大。当搅拌针移动速度50 mm·min^-1、旋转速度2000 r·min^-1时，焊核区金属和夹层中的混合粉末发生了充分的塑性变形，粉末圈分布连续且均匀。模拟结果表明：搅拌摩擦加工时最高温度区域出现在搅拌针附近，呈“碗状”分布，此时温度达到最大值491℃,焊核区金属和夹层中的混合粉末发生充分塑性变形和流动，模拟结果与试验结果一致。经过680℃发泡后，泡沫铝最大孔隙率为69.3%,平均泡孔直径为Φ130μm,屈服应力为3.2 MPa,平台应力值为2.9 MPa。     

闭孔泡沫铝力学性能的尺寸效应研究

进行具有不同尺寸的闭孔泡沫铝试件的准静态单轴压缩试验,获得了名义压缩应力-应变曲线。实验结果表明,闭孔泡沫铝的力学性能具有较为明显的尺寸效应。当厚度不变时,闭孔泡沫铝的屈服应力会随着压缩横截面的增大而有所提高;当压缩横截面不变时,闭孔泡沫铝的屈服应力先是随着试件厚度的增大而减小,然后趋向稳定。最后,对造成尺寸效应现象的相关机理进行了解释。     

发泡工艺参数对闭孔泡沫铝胞结构的影响

采用压缩空气法制备闭孔泡沫铝,研究空气流量、搅拌速度和发泡温度对胞结构的影响。结果表明泡沫铝的胞直径为4-11mm,密度为0.10-0.22g/cm3,孔隙率最高达96.3%;泡沫铝的胞直径随着空气流量和发泡温度的增大而增大,随搅拌速度的增大而减小,其中空气流量对胞直径的影响最显著;壁厚和结点尺寸随空气流量和搅拌速度的变化规律与胞直径相反;在相同的搅拌速度下,泡沫铝的密度随着胞直径的增大而减小且与胞直径存在对应关系,搅拌速度为600r/min时,关系式为ρ=0.0278 0.3602.e-0.132d。     

闭孔泡沫铝的导热性能

研究了孔隙率、孔径对闭孔泡沫铝合金导热系数的影响，结果表明，由于大量孔洞的存在，泡沫铝的导热系数较同样成分的实体材料显著下降，孔隙率在0．80—0.93范围内，约为实体材料的1／30—1／80，随着孔隙率的增加，导热系数迅速下降，而孔径对泡沫铝的导热系数影响不大．从串-并联和并-串联模型出发，分析了孔隙率对泡沫铝材料导热系数的影响，发现串-并联模型更能反映泡沫铝的结构特征，与实测值吻合更好。     

A symmetric and interconnected skeleton structural (SISS) model for predicting thermal and electrical conductivity and Young’s modulus of porous foams

A symmetric and interconnected skeleton structural (SISS) model is proposed for predicting the thermal and electrical conductivities and Young’s modulus of open-cell foams with hollow and solid struts. The model predicted the effective thermal and electrical conductivities of solid-strut aluminium foams and other open-cell foams for the entire porosity range. The SISS model provided upper and lower bounds for the effective thermal conductivity and Young’s modulus of hollow-strut open-cell nickel foams. The SISS model was also found to predict the effective thermal conductivity of closed-cell graphite foams, and the effective electrical conductivity and Young’s modulus of closed-cell aluminium foams with reasonable accuracy. By analogy, the SISS model might also be applied to other physical properties.     

开孔泡沫铝的低温热导率测量及其低温蓄冷应用研究

新型材料的应用对低温装置的发展起具有重大意义。为提高低温蓄冷装置的温度均衡性,一种孔隙率为63%的开孔泡沫铝材料最近在一种低温蓄冷装置中进行了实验研究。实验测试了样品从50 K到170 K的热导率,测试结果显示开孔泡沫铝在测试温度区间内热导率随温度降低而升高,其平均值为22W·(m·K)~(-1)。实验测试了开孔泡沫铝热导率对采用泡沫铝低温蓄冷装置的性能的影响。蓄冷装置中采用的相变材料为氮。实验中主要测试值为蓄冷装置在降温过程和融化过程中的温度值。实验结果显示,此装置上、下部分的最大温差小于0.5 K,远小于不采用开孔泡沫铝时的温差。随着低温蓄冷装置热导率的提高,蓄冷装置上、下部温差以及单个温度测定的温度波动均减小。     

Numerical investigation of conductive heat transfer in high-porosity foams

The conductive heat transfer in heterogeneous cellular materials is generally treated by defining the homogeneous effective thermal conductivity. For high-porosity foams, a very large number of empirical or semi-empirical models have already been proposed to evaluate this conductivity. Each approach considered different cellular morphologies and used different solution methods, leading to noticeable discrepancies. In order to estimate the reliability of these models, a numerical finite volume method computing the effective thermal conductivity of discretised two-phase heterogeneous materials was developed. It was applied to different regular open or closed cellular structures and to structures generated from tomographic images of polyvinyl chloride, expanded polystyrene and NiCrAl foams. The comparison with the results of the different models allows their degree of reliability and their domain of applicability to be estimated quantitatively.     

A study on thermal characteristics of non-contact hot-tool for rapid feature detailing (RFD) process

The rapid feature detailing (RFD) process utilizing the non-contact hot-tool has been developed to create detailed shapes on the surfaces of VLM-ST parts. The dimensional accuracy of the detailed shape is significantly dependent on process parameters such as heat input, shaping speed, and the gap between the hot-tool and EPS foam. The objective of this study is to investigate the influence of process parameters on thermal characteristics such as kerfwidth, depth of cut and temperature distribution in the EPS foam in order to obtain controllable conditions for feature detailing and to improve dimensional accuracy of the process. Several experiments were carried out to find the relationships between process parameters and kerfwidth, and between process parameters and depth of cut. Numerical analyses were performed to investigate the influence of process parameters on temperature distribution in the EPS foam sheet and to estimate the amount of the sheet melted away. In order to develop a numerical model of the RFD process, a radiation heat source model utilizing view factors and an anisotropic thermal conductivity are introduced. In terms of kerfwidth and depth of cut, the results of the numerical analysis were in agreement with the experimental results. From this, it has been confirmed that the proposed numerical model is an effective tool to predict the influence of process parameters. Based on these results, the controllable operating conditions for the RFD process are described.     

Tensile property of Al-Si closed-cell aluminum foam

1Introduction The unique properties of metallic foams make them useful in a number of potential application fields including damping,electromagnetic shielding,heat exchange,sound insulation,sound absorption,and energy absorption[1?4].The closed-cell alumi…     

双重孔径泡沫金属材料的强度和热性能多目标优化设计

对双重孔径泡沫金属稳态热传导过程进行了数值模拟, 发现相同密度下双重孔径泡沫金属导热系数高于单一孔径泡沫金属, 但随着孔径比增大, 材料导热系数减小. 通过对有限元计算结果的多项式拟合得到了目标函数, 建立了包含强度 、隔热和轻质3个目标函数的多目标优化设计数学模型, 讨论了构件质量一定的情况下双重孔径泡沫金属材料设计参数的选取,  获得了满足强度要求, 同时隔热性能最优的泡沫金属孔径比、密度和构件厚度. 泡沫金属构件隔热参数—屈服应力图表明, 作为同时满足承载和隔热要求的泡沫金属板构件, 选用双重孔径泡沫金属的构件综合性能要显著优于单一孔径泡沫金属构件.     

Numerical Study of a Thermal Energy Storage Device Utilizing Graphite Foam Infiltrated with a Phase Change Material

Phase change materials (PCM) utilized for energy storage have notoriously low thermal conductivities. As a result, systems based only on a PCM have large internal thermal gradients and slow reaction times making them impractical for most applications. To overcome these issues, various approaches have been utilized to increase the conductivity of the PCM systems. One approach includes the utilization of porous, high thermal conductivity graphite foam infiltrated with a PCM. Here, a numerical approach was employed in order to study the graphite foam/PCM thermal energy storage system (TES). The numerical model was constructed to emulate an experimental set-up allowing for comparisons between the two. The numerical simulation results exhibited accurate time-dependent temperatures at various locations as well as a history of the melt-front’s progression when compared to the experimental data. Due to the model’s successful capture of the transient response of the TES, it is feasible to employ the numerical procedure for designing subsequent thermal energy storage systems.