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.     

Analytical expressions for effective thermal conductivity of composite materials with inclusions of square cross-section

Thermal conductivity of composite materials with periodically distributed cylindrical inclusions of square cross-section is investigated. Analytical interpolation formula for the effective thermal conductivity in transversal direction valid in the entire range of volume fraction of inclusions and value of their thermal conductivity is derived. The methods of asymptotic homogenization, boundary shape perturbation and asymptotically equivalent functions are used. Asymptotic expansions of the effective thermal conductivity in limiting cases of size of inclusions and their thermal conductivity are obtained. The analytical expressions are evaluated numerically and compared to other models. It is shown that the discrepancy between these results is very low in all cases.     

Dielectric properties of composite materials containing aligned carbon nanotubes

This paper presents a study of the electrodynamic properties of polymer-matrix composite materials containing a filler in the form of multiwalled carbon nanotubes. We have examined the effect of filler alignment in the composites on their interaction with electromagnetic radiation. The composite materials have an anisotropic electrical conductivity, dielectric permittivity, and electromagnetic radiation attenuation coefficient because an applied electric field produces a preferential filler alignment direction.     

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.     

聚偏氟乙烯基复合材料的制备及介电性能

为有效改善聚合物基复合材料的介电性能,兼顾高介电常数和低填料量同时并存,采用以聚偏氟乙烯(PVDF)为基体树脂,钛酸钡(BT)和石墨烯(GNP)分别为介电填料和导电填料,在BT-GNP/PVDF复合体系内部构建微电容器结构.采用溶液法和热压法制备GNP/PVDF薄膜和BT-GNP/PVDF复合薄膜.结果表明,BT和GN...     

Analysis of the effective conductivity of composite materials in the entire range of volume fractions of inclusions up to the percolation threshold

The analytical interpolation formulas for the effective electrical conductivity of fiber-reinforced and particulate composites for any volume fractions of inclusions are derived in the present paper. The Garnett formulas are used for a limiting case of small volume fractions of inclusions. And the formulas based on the Shklovskii–De Gennes model are adopted for a limiting case of large volume fractions of inclusions approaching the percolation threshold. The derivation is based on application of the method of asymptotically equivalent functions. This approach presents a natural generalization of the two-point Padé approximants to the case, when in one of the limits the interpolated function cannot be represented in the form of power series. The application of this interpolation technique made it possible to derive the formulas for the effective conductivity of fiber-reinforced and particulate composites with very high volume fractions of inclusions, up to the percolation threshold. The numerical results are compared with the known asymptotic expressions, and also with the existing exact expressions in some limiting cases, for example, in the case of statistically equivalent arrangement of the constituent materials. Comparison with the experimental data confirms the satisfactory accuracy of the obtained analytical results.     

泡沫金属基复合相变材料的有效导热系数研究

为了更有效地预测泡沫金属基复合相变材料(composite phase claange material,CPCM)的导热性能,提出了一种新的CPCM相分布模型,以此为基础建立了带有空穴子模型的简化传热模型,并利用等效热阻法推导得到泡沫金属基CPCM有效导热系数的通用计算式.传热模型考虑了相变过程中相变材料(plnase change material,PCM)的体积变化和空穴分布的影响,使得有效导热系数的计算结果更加符合实际.     

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.     

Fracture analysis of aluminium matrix composite materials reinforced with (Ni3Al)p

This paper studies the influence of Ni₃Al intermetallic particles on the fracture behaviour of aluminium matrix (2014) composite materials. Intermetallics were obtained by mechanical alloying and by atomisation. The composite materials were manufactured by mixing, uniaxial compacting of a preform, and subsequent extrusion without canning or degassing. The study considered materials in extruded state and after T6 heat treatment. Assessments were made from the viewpoint of microstructure (by means of optical and scanning electron microscopy), and studying the reactions between the matrix and the reinforcement. These reactions produce a highly copper-enriched interphase. The influence of the reinforcement and state of the alloy on the fracture behaviour of the composite materials was studied through scanning electron microscopy.     

Tensile properties of high strength polyacrylonitrile (PAN)-based and high modulus pitch-based hybrid carbon fibers-reinforced epoxy matrix composite

The tensile properties of high strength polyacrylonitrile-based (IM600) and high modulus pitch-based (K13D) hybrid carbon fibers-reinforced epoxy matrix composite (CFRP) were investigated. Fiber orientation of the hybrid CFRP specimen was set to [0_(IM600)/0_(K13D)]_2S. The fiber volume fraction of the hybrid CFRP specimen was 55.7 vol% (IM600: 29.3 vol%, K13D: 26.4 vol%). The tensile stress–strain curve of the hybrid CFRP specimen shows a complicated shape (jagged trace). By the high modulus K13D CFRP layers, the hybrid CFRP specimen shows the intermediate modulus in the initial stage of loading. Subsequently, when the K13D CFRP layers begin to fail, the high strength IM600 CFRP layers would hold the load (strength) and the material continues to endure high load without instantaneous failure. Because higher strength fiber can help the load for a certain time after failure occur, the hybrid composite could be considered one example of a material possessing preventing instantaneous failure. The Weibull statistical distributions of the mono (IM600 and K13D) and the hybrid CFRP specimens were also examined. The Weibull modulus for the mono CFRP specimens was calculated to be 22.9 for the IM600 CFRP specimen and 14.4 for the K13D CFRP specimen, respectively. The Weibull modulus for the hybrid CFRP specimen was calculated to be 39.6 for the initial fracture strength and 20.6 for the tensile fracture strength, respectively. The Weibull modulus for the initial fracture strength is higher than that for the K13D CFRP specimen and the Weibull modulus for the tensile fracture strength is almost similar to that for the IM600 CFRP specimen.     

The influence of thermal history on the mechanical properties of poly(ether ether ketone) matrix composite materials

The purpose of this study is to provide insight into the microstructural factors that affect the flexural fatigue performance of carbon-fibre-reinforced poly(ether ehter ketone) (PEEK) composites. Specifically, the effect of the degree of crystallinity on the mechanical properties is examined at two crystallinity levels of the as-received composites (35%) and of quenched composites (10%). Higher static flexural strength and modulus as well as longer fatigue life are observed for the higher crystallinity level. By varying the loading angle with respect to the fibre direction it is shown that the crystallinity effect is not matrix dependent alone. Rather, a strong effect is evident in the fibre direction, which is attributed to the influence of the transcrystalline layer formed on the fibre surface in the high-crystallinity material. As a result, the longitudinal fatigue life at 1·7GPa of the 35% crystallinity material is three orders of magnitude higher than that of the 10% crystallinity composite.     

Electrical properties of dielectric matrix with spherical inclusions of metal

The dielectric permittivity and electrical conductivity of a dielectric matrix with spherical inclusions of metal are calculated. The theoretical formula is verified experimentally and compared with other known formulas.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 6, pp. 1000–1007, December, 1976.     

The mechanical properties of friction welded aluminium-based metal–matrix composite materials

The optimum joining parameters for the friction joining of aluminium-based metal–matrix composite (MMC) materials are examined. The properties of MMC/MMC, MMC/alloy 6061 and alloy 6061/alloy 6061 joints are derived following detailed factorial experimentation. The mechanical properties of the joints are evaluated using a combination of notch tensile testing and also conventional tensile and fatigue testing. The frictional pressure has a statistically-significant effect on the notch tensile strength of joints produced in all base material combinations. The upset pressure has only a statistically-significant influence on the notch tensile strength properties of alloy 6061/alloy 6061 joints. The notch tensile strengths of MMC/alloy 6061 joints are significantly lower than MMC/MMC and alloy 6061/alloy 6061 joints for all joining parameter settings. The fatigue strength of MMC/MMC joints and alloy 6061/6061 joints are also poorer than the as-received base materials. This revised version was published online in November 2006 with corrections to the Cover Date.     

On the effective conductivity of composite materials

A composite conductive material, which consists of fibers of a high conductivity in a matrix of low conductivity, is discussed. The effective conductivity of the system considered is calculated in Clausius-Mossotti approximation. Obtained relationships can be used to calculate the conductivity of a matrix, using experimentally measured parameters. Electric fields in the matrix and the inclusions are calculated. It is shown that the field in a low-conductivity matrix can be much higher than the external applied one.     

Optimization of pre-metal Dielectric (PMD) materials

It is very important to select superior interlayer pre-metal dielectric (PMD) materials that can act as a penetration barrier to various impurities created by the chemical mechanical polishing (CMP) process. In this paper, hot carrier degradation and device characteristics were studied on various materials of PMD-1 layers, which included low-pressure tetra-ethyl-ortho-silicate glass (LP-TEOS), Si-rich (SR)-oxide, plasma-enhanced (PE)-oxynitride, PE-nitride and PE-TEOS films. Pressure cooker test (PCT) analysis was used to obtain the electrical characteristics of devices, such as the shifts in threshold voltage and transconductance as a function of stress time, junction leakage current and breakdown voltage of field transistors with variation of these PMD-1 materials. Also, the most effective PMD-1 materials which can prevent degradation effects due to hot carrier stress were investigated. From experimental results, it is clearly shown that silicon oxide turned out to be a better PMD-1 material than both PE-oxynitride and PE-nitride. From the results, it is suggested that LP-TEOS film is the best PMD-1 material among the silicon oxide samples. © 2001 Kluwer Academic Publishers     

Dielectric properties of the ferroelectric composite (NaNO2)0.9/(BaTiO3)0.1

The temperature and frequency dependences of dielectric properties of the ferroelectric composite (NaNO₂)_0.9/(BaTiO₃)_0.1 have been studied. It was shown that in the composites the mutual influence of the components may lead to the expansion of incommensurate phase existence in NaNO₂. The greatest contribution to the low-frequency dielectric constant of the composite is due to the Maxwell–Wagner polarization.     

Simple and precise measurements of fibre volume and void fractions in metal matrix composite materials

A method for determining the fibre volume fraction, V _f and the void fraction, V _g, in a metal matrix composite (MMC) material is described. These quantities are determined from specimen weight measurements in air and in a liquid using a laboratory balance. For a material without voids, V _f can be determined with an uncertainty less than 0.5% with a balance precision of 0.01%. By making the same measurements before and after etching away the matrix, using the same balance precision, V _f and V _g can be determined to an uncertainty of about 3 and 6%, respectively. It is also shown theoretically that by indenting a specimen containing no fibres and only a uniform distribution of small voids, the void fraction can also be determined from weight measurements before and after indentation.     

Wear behaviour of aluminium matrix composite materials

Wear behaviour of aluminium matrix composites is characterized by the dry spindle wear test under various conditions (volume fractions of reinforcements, sliding distances and speeds). Wear resistance of composites is improved due to the presence of reinforcements, but no noticeable improvements are observed in the wear resistance with more than 20% addition of reinforcements. To analyse wear mechanisms, wear surfaces are examined by scanning electron microscopy (SEM). The major wear mechanisms of discontinuous metal matrix composites (MMC)s are strongly dependent on sliding speeds. Dominant mechanism is the adhesive-abrasive wear at low and intermediate sliding speeds, and melt wear at high sliding speeds. Weight loss is linearly increased with the sliding distance. The effect of reinforcements' orientations on wear behaviours is also discussed.