Thermal conductivity of a composite material reinforced by regularly distributed spheroidal particles

A rigorous solution of the problem of determining the effective thermal conductivity tensor of a composite material with regularly distributed spheroidal interstitials is presented.Institute of Superhard Materials, Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 4, pp. 497–504, April, 1994.     

Identification of effective properties of particle reinforced composite materials

For the determination of effective elastic properties an energy averaging procedure has been used for particle reinforced composite materials. This procedure is based on finite element calculations of the deformation energy of a characteristic volume element. The proposed approach allows the determination of effective properties of particle reinforced composite with acceptable precision. The calculated effective properties of the composite are found in range between upper and lower Hashin-Shtrikman bounds. The averaging elastic properties of the composite depend on the properties of the particles, matrix volume fraction of the particles and some parameters taking into account the influence of the interphase between matrix and particles. These dependencies can be presented by simple analytical functions approximatically. An identification procedure basing on numerical experiments allows the estimation of the unknown approximation parameters. The obtained functions describe precisely the numerical data for any relationship between material constituents.     

基于五相球模型确定含涂层空心微球复合材料的有效模量

利用推广的五相球模型得到了含涂层空心微球填充复合材料的有效体积模量、剪切模量和杨氏模量预测的理论公式。分析了复合材料有效模量同空心微球壁的厚度、填充体积分数、涂层厚度等参数的关系。为了说明本文结果的有效性, 将五相球模型退化为不含涂层空心球填充复合材料的情况, 并与文献中的实验数据进行对比。算例计算表明: 涂层较薄时, 填料体积分数越大, 空心微球壁相对越厚, 弹性模量就越大。当填料体积分数最大时, 在空心微球壁相对最薄处, 弹性模量最低。      

Tensile properties and microstructures of Al composite reinforced with BN particles

Al–4.5 wt% Mg alloys reinforced with and without BN were fabricated by pressureless infiltration method and then their tensile properties and microstructures were analyzed. Since the spontaneous infiltration of molten metal occurred at a temperature of 800 °C for 1 h under nitrogen atmosphere, it was possible to fabricate the Al composites reinforced with BN and control alloy without BN. A large increase in strength in the case of the control alloy is related to the in situ formation of AlN particles as well as grain size refinement. In the composite reinforced with BN, additional AlN was formed by the interfacial reaction of the BN and Al melt as well as AlN by the in situ reaction. In addition, the grain size in the composite reinforced with 7.5 vol% BN further decreased to about 4.0 μm and exhibited approximately 3.5 times reduction in the grain size of the commercial alloy. Consequently, a further strengthening in the composite resulted from both the BN artificially added and AlN formation (by the in situ reaction and interfacial reaction) and grain refinement.     

A multiscale approach and microstructure design of the elastic composite behavior reinforced with natural particles

The morphology characterization and computational methods favored numerical simulation and design of microstructures. Indeed, the multiscale approaches enable us to determine the elastic properties of materials. In this paper, the objective is to develop a three-dimensional microstructure of biocomposites containing natural particles. The biocomposite is made of polypropylene matrix mixed with natural fillers. The image is obtained using the microscope. We describe a serial sectioning process and finite element simulations to reproduce, visualize and model these microstructures. Statistical methods are introduced to study the representativity of specimen. The statistical representative volume element is introduced to determine the minimum volume which provides the representativeness. This statistical volume is compared with experimental and numerical ones.     

Creep property of composite solders reinforced by nano-sized particles

In the present work the creep properties of Sn37Pb and Sn0.7Cu based composite solders with nano-sized metallic Cu, Ag and nano-sized oxide Al₂O₃, TiO₂ reinforcement particles have been studied. First, a series of volume percentages of reinforcements were selected for optimizing the content of particles. Then, the composite solder with optimum volume fraction of the reinforcement particles, corresponding to maximum creep rupture life, is selected for investigating the effect of applied stress level and test temperature on creep rupture life of the composite solder joints. In the creep rupture life test, small single-lap tensile-shear joints were adopted. The results indicate that all the composite solders have improved creep resistance, comparing to the eutectic Sn37Pb solder and the Sn0.7Cu lead-free solder. The creep rupture life of the composite solder joints is first increased with the increase in the volume fraction of reinforcement in the composite solders. Then, the creep rupture life is decreased, as the reinforcement content exceeds a certain value. The creep rupture life of the solder joints is decreased with the increase of applied stress and testing temperature. Moreover, the reinforced efficiency of nano-sized Ag particles is the best in all the tested nano-sized reinforcements for the Sn37Pb based and Sn0.7Cu based composite solders, when the particles contents are in their own optimum content.     

A theoretical approach for the thermal expansion behavior of the particulate reinforced aluminum matrix composite Part I A thermal expansion model for composites with mono-dispersed spherical particles

Microstructural observation revealed that the increase in the volume fraction of SiC particles lowers the coefficient of thermal expansion (CTE) of the composite, and the CTE of the metal matrix composites is proportional to the size of the Si phase. To analyze the thermal expansion behavior of aluminum matrix composites, a new model for the CTE of the mono-dispersed binary composite on the basis of Ashelby's cutting and welding approach was proposed. In the theoretical model, it was considered that during cooling relaxation of residual stresses could create an elasto-plastic deformation zone around a SiC or Al₂O₃ particle in the matrix. The size of reinforced particles and other metallurgical factors of the matrix alloy and composite were also considered. In this model, the interacting effect between the reinforced hard particle and the soft matrix is considered by introducing the influence of the elasto-plastic deformation zone around a particle, which is distinguished from the previous models. It was revealed that the CTE of the composite are influenced by the particle volume fraction, the elastic modulus and Poisson's ratio as well as the elasto-plastic deformation zone size and the particle size.     

A micro-mechanics model for composites reinforced by regularly distributed particles with an inhomogeneous interphase

Based on the Mori–Tanaka method, a micro-mechanics model is developed to study the effective elastic properties of composites reinforced by regularly distributed particles. The spatial distribution of particles is supposed to be cube symmetric in the three-dimensional space, and the corresponding finite element method (FEM) computation has been performed through a unit cell model. Additionally, particle interaction and distribution are simultaneously taken into account by using the strain Green’s function, and the specified strain Green’s function is determined by utilizing the necessary conditions of geometric symmetry. In order to analyze particle size effect on the effective properties of composites, the Double-inclusion configuration and related theory are introduced to describe the role of the interphase between the matrix and particles. Finally, the overall elastic properties of the composite with regularly distributed particles are described by three independent elastic constants expressed in the explicit form, and the accuracy of the developed model is verified by comparing with FEM results.     

纤维增强复合材料弹塑性性能的细观研究

基于Mori-Tanaka方法和Eshelby等效夹杂理论,建立弹性阶段基体和纤维平均应力之间的桥联矩阵,导出了该矩阵各元素的显式。鉴于工程实际材料对柔度矩阵对称性的要求并考虑组分材料物理性能和细观几何特征等因素的影响,对所导出的桥联矩阵进行合理简化。引入与基体等效塑性应变相关联的修正参数,以此确定纤维和基体中应力分配。数值结果表明,本文中建立的复合材料非线性理论模型与实验结果吻合较好。      

A novel approach to a fine particle coating using porous spherical silica as core particles

The applicability of porous spherical silica (PSS) was evaluated as core particles for pharmaceutical products by comparing it with commercial core particles such as mannitol (NP-108), sucrose and microcrystalline cellulose spheres. We investigated the physical properties of core particles, such as particle size distribution, flow properties, crushing strength, plastic limit, drying rate, hygroscopic property and aggregation degree. It was found that PSS was a core particle of small particle size, low friability, high water adsorption capacity, rapid drying rate and lower occurrence of particle aggregation, although wettability is a factor to be carefully considered. The aggregation and taste-masking ability using PSS and NP-108 as core particles were evaluated at a fluidized-bed coating process. The functional coating under the excess spray rate shows different aggregation trends and dissolution profiles between PSS and NP-108; thereby, exhibiting the formation of uniform coating under the excess spray rate in the case of PSS. This expands the range of the acceptable spray feed rates to coat fine particles, and indicates the possibility of decreasing the coating time. The results obtained in this study suggested that the core particle, which has a property like that of PSS, was useful in overcoming such disadvantages as large particle size, which feels gritty in oral cavity; particle aggregation; and the long coating time of the particle coating process. These results will enable the practical fine particle coating method by increasing the range of optimum coating conditions and decreasing the coating time in fluidized bed technology.     

The effective thermal conductivity of a composite material with spherical inclusions

A new method is presented for calculating the effective thermal conductivity of a composite material containing spherical inclusions. The surface of a large body is assumed kept at a uniform temperature. This body is in contact with a composite material of infinite extent having a lower temperature far from the heated body. Green's theorem is then used to calculate the rate of heat transfer from the heated body to the composite material, yielding $$k_e /k = 1 + \frac{{3(\alpha - 1)}}{{[\alpha + 2 - (\alpha - 1)\phi ]}}\{ \phi + f(\alpha )\phi ^2 + 0(\phi ^3 )\} $$ where k _e is the effective thermal conductivity, k is the thermal conductivity of the continuous phase, α is the ratio of the thermal conductivity of the spherical inclusions to k, and φ is the volume fraction occupied by the dispersed phase. The function f(α) is presented in this work. Although a similar result has been found previously by renormalization techniques, the method presented in this paper has merit in that a decaying temperature field is used. As a result, only convergent integrals are encountered, and a renormalization factor is not needed. This method is more straightforward than its predecessors and sheds additional light on the basic properties of two-phase materials.     

Effective conductivity of a composite of poly-dispered spherical particles in a linear continuum

Rayleigh's method is used to find the electric potentials of a composite of poly-dispered spherical particles in a linear continuum in an external electric field. Based on the solutions of potentials, analytical formula for the effective electric conductivity is derived. Based on the formula, several factors, such as the number of spherical inclusions, the spatial distribution of the spheres, the contrast ratio _i / _h (where, _i and _h are the conductivities of the spherical inclusion and the host medium, respectively) and volume fraction of the inclusions, are discussed. Our results show that at high volume fraction, the effective conductivity is also affected by the spatial distribution of the inclusions.     

Development of Cu particles and Cu core-shell particles reinforced Al composite

Copper particles were incorporated and retained in elemental state in an aluminium matrix by friction stir processing thereby producing a non-equilibrium particulate composite. The processed Al–Cu_p composite exhibited improved strength with significantly high ductility. The composite was stable up to a temperature of more than 300°C. Thermal exposure at 350°C for more than 10 min led to diffusion of Cu atoms into the Al matrix forming a core-shell type structure in the Cu particles and thus producing an Al–Cu core-shell composite. The shell consists of multiple layers, the thickness of which was controllable.     

Multi-coating inhomogeneities approach for the effective thermo-electro-elastic properties of piezoelectric composite materials

This work presents a micromechanics-based model to predict the effective thermo-electro-elastic properties of a piezoelectric composite materials containing ellipsoidal multi-coated inhomogeneities. A finite element analysis is also performed for two-phase piezoelectric composite materials using ABAQUS finite element software. The results obtained from the multi-coating homogenization method show good agreement with the existing experimental results and the finite element results. The inhomogeneities’s shape effect as well as the poling direction and the coating effects are investigated. The results show that a proper choice of materials and inhomogeneities’s geometry can lead to the desired thermo-electro-elastic properties.     

颗粒增强铝基功能梯度复合管研究

对强化颗粒进行了预处理,通过控制搅拌条件及感应炉供电功率等参数,使颗粒直接加入到基体铝合金中,并在浆体中呈现不同的分布,再通过调整其它的工艺参数,利用水平式离心铸造机制了三种具有不同强化部位和不同颗粒分布的功能梯度复合管,外层强化,内层强化以及内外层同时强化,结果表明：功能梯度复合管的显微硬度与颗粒分布具有良好的对应关系,而且显微组织也呈呈现梯度变化,强化部位的多样化可为功能梯度厚壁复合管的应用开辟新的领域。     

Effect of carbon nanotube waviness on the effective thermoelastic properties of a novel continuous fuzzy fiber reinforced composite

This paper deals with the investigation of the effect of carbon nanotube (CNT) waviness on the effective coefficient of thermal expansion (CTE) of a novel continuous fuzzy fiber reinforced composite (FFRC). This novel FFRC is composed of carbon fibers, sinusoidally wavy CNTs and epoxy matrix. The sinusoidally wavy CNTs are radially grown on the circumferential surfaces of the carbon fibers. Analytical micromechanics model based on the method of cells (MOC) approach is derived to investigate the influence of the waviness of CNTs on the effective CTEs of the FFRC. The present study reveals that if the amplitudes of the radially grown sinusoidally wavy CNTs are parallel to the axis of the carbon fiber then the thermoelastic properties of the FFRC are significantly improved over those of the FFRC being composed of straight CNTs.     

新型纳米结构颗粒增强无铅复合钎料性能

为了解决传统复合钎料制备中强化颗粒容易粗化的问题,提高无铅复合钎料的性能,选用共晶Sn-3.5Ag、Sn-3.0Ag-0.5Cu钎料作为基体,3种不同类型具有纳米结构的有机-无机笼型硅氧烷齐聚物(POSS) 颗粒作为增强相而制成复合钎料。研究了复合钎料的铺展性能、钎焊接头的力学性能和抗蠕变性能。结果表明,复合钎料的润湿性能均优于基体钎料的润湿性能,复合钎料钎焊接头的剪切强度和蠕变断裂寿命均明显提高。在相同条件下,Sn-Ag-Cu基复合钎料钎焊接头的性能优于Sn-Ag基复合钎料钎焊接头。      

Mechanical properties of rolled A356 based composites reinforced by Cu-coated bimodal ceramic particles

Three kinds of A356 based composites reinforced with 3 wt.% Al₂O₃ (average particle size: 170 μm), 3 wt.% SiC (average particle size: 15 μm), and 3 wt.% of mixed Al₂O₃–SiC powders (a novel composite with equal weights of reinforcement) were fabricated in this study via a two-step approach. This first process step was semi-solid stir casting, which was followed by rolling as the second process step. Electroless deposition of a copper coating onto the reinforcement was used to improve the wettability of the ceramic particles by the molten A356 alloy. From microstructural characterization, it was found that coarse alumina particles were most effective as obstacles for grain growth during solidification. The rolling process broke the otherwise present fine silicon platelets, which were mostly present around the Al₂O₃ particles. The rolling process was also found to cause fracture of silicon particles, improve the distribution of fine SiC particles, and eliminate porosity remaining after the first casting process step. Examination of the mechanical properties of the obtained composites revealed that samples which contained a bimodal ceramic reinforecment of fine SiC and coarse Al₂O₃ particles had the highest strength and hardness.