Air-coupled ultrasonic investigation of multi-layered composite materials

Air-coupled ultrasonics is fine alternative for the immersion testing technique. Usually a through transmission and a pitch-catch arrangement of ultrasonic transducers are used. The pitch-catch arrangement is very attractive for non-destructive testing and evaluation of materials, because it allows one-side access to the object. However, this technique has several disadvantages. It is sensitive to specularly reflected and edge waves. A spatial resolution depends on a distance between the transducers. A new method for detection and visualisation of inhomogeneities in composite materials using one-side access air-coupled ultrasonic measurement technique is described. Numerical predictions of Lamb wave interaction with a defect in a composite material are carried out and the interaction mechanism is explained. Experimental measurements are carried out with different arrangements of the transducers. The proposed method enables detect delamination and impact type defects in honeycomb materials.     

空气耦合超声检测复合材料研究综述

复合材料普遍具有高比强度、高比刚度、高模量、耐腐蚀等优异性能,广泛应用于飞机机翼、导弹外壳、航空发动机壳体等部位。制造和服役过程中各类缺陷影响复合材料的力学性能和服役性能,必须采用有效的方法准确检测和评估复合材料中各类缺陷。空气耦合式超声检测具有完全非接触、非侵入、无损伤和无需耦合剂的特点,能够很好地运用于复合材料的在线和在位检测。该文就近年来空气耦合超声检测技术的研究现状进行了系统综述,简明扼要地分析和介绍了当前空气耦合超声检测的研究热点及进展,重点介绍了1-3型压电复合材料换能器、信号处理技术、相控聚焦式空气耦合超声检测、超声在复合材料的传播特性及其与缺陷交互作用的研究现状,探讨了空气耦合超声无损检测技术与仪器的发展方向,总结了目前空气耦合超声检测的研究热点问题,最后展望了空气耦合超声检测的发展趋势和应用前景。     

Mass attenuation coefficients of composite materials by Geant4, XCOM and experimental data: comparative study

The main goal of this present study is focused on testing the applicability of Geant4 electromagnetic models for studying mass attenuations coefficients for different types of composite materials at 59.5, 80, 356, 661.6, 1173.2 and 1332.5 keV photon energies. The simulated results of mass attenuation coefficients were compared with the experimental and theoretical XCOM data for the same samples and a good agreement has been observed. The results indicate that this process can be followed to determine the data on the attenuation of gamma rays with the several energies in different materials. The modeling for photon interaction parameters was standard for any type of composite samples. The Geant4 code can be utilized for gamma ray attenuation coefficients for the sample at different energies, which may sometimes be impractical by experiment investigation.     

SiC-Based Composite Materials Obtained by Siliconizing Carbon Matrices

We have developed a method for fabrication of parts of complicated configuration from composite materials based on SiC ceramics, which employs the interaction of silicon melt with the carbon matrix having a certain composition and porosity. For elevating the operating temperatures of ceramic components, we have developed a method for depositing protective silicon-carbide coatings that is based on the interaction of the silicon melt and vapor with carbon obtained during thermal splitting of hydrocarbon molecules. The new structural ceramics are characterized by higher operating temperatures; chemical stability; mechanical strength; thermal shock, wear and radiation resistance; and parameters stability.     

Interaction of fast electrons and gamma-quanta with radiation protection ferric oxide composites

Physical processes of fast electron and gamma-radiation beam interaction with radiation protection ferric oxide composite materials are investigated together with dependences of energy (flux) accumulation and transmission coefficients on the gamma-radiation energy and thickness of a protective screen. Integral characteristics of radiation protection materials are calculated. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 66–71, November, 2008.     

Modeling and simulation of mechanical properties of nano-particle filled materials

With the recent advances in nanoscale science and engineering, materials containing reinforcement with superior mechanical properties can be found in many advanced products. The accurate prediction of the mechanical properties of this class of composite materials is important to ensure the reliability of the products. Characterization methods based contact probe such as nano-indentation and scratch tests havebeen developed in recent years to measure the mechanical properties of the new class of nanomaterials. This paper presents a constitutive modeling framework for predicting the mechanical properties of nanoparticle reinforced composite materials. The formulation directly considers the effects of inter-nanoparticle interaction and performs a statistical averaging to the solution of the problem of two-nanoparticle interaction. Final constitutive equations are obtained in analytical closed form with no additional material parameters. The predictions from the proposed constitutive model are compared with experimental measurement from nano-indentation tests. This constitutive model for nanoparticle reinforced composites can be used to determine the volume concentration of the reinforcing nanoparticles in nano-indentation test.     

Modeling of light absorption and scattering by metal nanoparticles coated with organic dye J-aggregate

The results of the theoretical study of optical properties of composite nanoparticles consisting of a metal core (Ag, Au, Cu, Al, Ni, Cr) and a J-aggregate shell of organic dye are presented. Light extinction, absorption, and scattering coefficients in colloidal solutions were calculated within the model based on the Mie theory modified taking into account dimensional phenomena and complemented by calculations of complex dielectric functions of the metal core and J-aggregate shell. The model adequately explains the features observed in light absorption and scattering spectra by hybrid nanoparticles, associated with the plasmon resonance in the metal core and with electronic excitation of the J-aggregate. The strong dependence of the results on geometrical parameters of nanoparticles and dielectric constants of core and shell materials was demonstrated. Methods for controlling the effects of the plasmon-exciton interaction in the system and optical properties of composite materials developed based on nanoparticles under study are discussed.     

Guided waves in anisotropic and quasi-isotropic aerospace composites: Three-dimensional simulation and experiment

Three-dimensional (3D) elastic wave simulations can be used to investigate and optimize nondestructive evaluation (NDE) and structural health monitoring (SHM) ultrasonic damage detection techniques for aerospace materials. 3D anisotropic elastodynamic finite integration technique (EFIT) has been implemented for ultrasonic waves in carbon fiber reinforced polymer (CFRP) composite laminates. This paper describes 3D EFIT simulations of guided wave propagation in undamaged and damaged anisotropic and quasi-isotropic composite plates. Comparisons are made between simulations of guided waves in undamaged anisotropic composite plates and both experimental laser Doppler vibrometer (LDV) wavefield data and dispersion curves. Time domain and wavenumber domain comparisons are described. Wave interaction with complex geometry delamination damage is then simulated to investigate how simulation tools incorporating realistic damage geometries can aid in the understanding of wave interaction with CFRP damage. In order to move beyond simplistic assumptions of damage geometry, volumetric delamination data acquired via X-ray microfocus computed tomography is directly incorporated into the simulation. Simulated guided wave interaction with the complex geometry delamination is compared to experimental LDV time domain data and 3D wave interaction with the volumetric damage is discussed.     

Preparation and XPS study of X-ray photochromic transparent BiOI/nylon11 composite film

Nylon11 film immersed in BiI₃–ethanol solution was used for in situ generation of transparent BiOI/nylon11 X-ray photochromic composite materials via integration of the hydrolyzate (BiOI) of BiI₃ into nylon11. The obtained BiOI/nylon11 composite film shows a reversible photochromic effect, changing the color from orange-red to brownish black under soft X-ray irradiation and back to orange-red after air exposure. X-ray photoelectron spectroscopy (XPS) results show that the oxidation state of Bi atoms in BiOI/nylon11 composite film does not change before and after changing the color. Angle-resolved XPS analysis reveals that BiOI in nylon11 film is well distributed within an infiltration depth of about 10 nm. The source of the X-ray photochromic effect for transparent BiOI/nylon11 composite film may be related to oxygen as well as the interaction between BiOI and the amide groups. The oxygen AT% in the composite film decreases with increasing X-ray irradiation time. The present method for preparing transparent BiOI/nylon11 X-ray photochromic composite materials is facile and low cost. The X-ray photochromic effect has potential applications in some technology fields. For example, it can be used to create temporary patterning in a colored composite material surface.     

The role of interactions at interfaces of glass-fiber reinforced composites

The performance of glass-fiber reinforced composite materials is strongly dependent on adhesion at the fiber-matrix interface. This study has considered the effect of parameters such as wettability, mechanical interlocking due to diffusion, and specific interactions on adhesion. The surface characteristics of treated and untreated glass fibers were studied by inverse gas chromatography. Donor/acceptor concepts were used to calculate a specific (acid/base) interaction parameter for fiber/matrix pairs. Tensile strengths of composites with Nylon-6,6 and polyethylene correlated with both acid-base and dispersive interactions. Initial attempts were made to separate and quantify contributions to interfacial bonding from dispersive forces, acid/base forces, diffusion and the mechanical interlocking of constituents. Findings were supported by scanning electron microscopy of the fracture surfaces of composite samples.     

Effect of surface roughness of chitosan-based microspheres on cell adhesion

Microspheres are novel candidate materials for microcarriers and tissue-engineering scaffolds. Chitosan microspheres were selected as the base materials because of their excellent properties for biomedical applications. But their smooth surfaces were not adapted for cell attachment. Hence, in order to improve the roughness of chitosan microspheres, β-TCP/chitosan composite microspheres were developed. From SEM photographs, the coarse surfaces of composite microspheres were observed, there were some ceramic particles standing out of the chitosan matrix. And their roughness measured by profilometers was about 2.0 μm. Mouse MC3T3-E1 osteoblasts were seeded on the microspheres for evaluating the attachment interaction between cells and materials. According to the ESEM photographs and MTT assay, the adherence and proliferation of osteoblasts on the surfaces of modified microspheres were better than those on the chitosan microspheres, which were mainly attributed to the improved roughness of surface.     

高浓度纤维增强材料介电特性计算方法

针对复合材料的微观结构非均匀和各向异性特点带来的数值方法计算慢、内存消耗大的问题,利用均匀化方法计算纤维增强复合材料的等效电磁参数.采用了纤维低体积添加比至高体积添加比的迭代方法,同时提出了一个描述材料微观结构的修正的特征长度,将现有的均匀化方法推广至非准静态(微波频段)条件下高纤维浓度情况.提出的修正的均匀化模型可直接用于反射系数、屏蔽效能等计算,其屏蔽效能与实际微观结构复合材料的数值仿真结果进行了对比,验证了提出的等效电磁参数计算公式的有效性和频率适用范围.     

Tuneability amplification factor and loss of high-contrast composites

The problem of tuneability of nonlinear ferroelectric–dielectric composite materials is addressed. Attention is concentrated on the analysis of the tuneability amplification factor, K, of a composite material, which is introduced as the ratio of the effective tuneability of a composite material to the tuneability of its ferroelectric (tuneable) component. Previously, ferroelectric–dielectric composite materials have been designed with an effective tuneability amplification factor slightly greater than 1 (i.e. 1.1–1.4) [A.K. Tagantsev et al., J. Electroceramics 11 (2003) p.5; A.G. Kolpakov et al., J. Electroceramics 18 (2007) p.129]. It is demonstrated that the tuneability amplification factor can take values significantly greater than 1. Numerical prototypes (structural designs integrated with finite element method tools) of microstructures are presented with K in the range 3 to 30. The effective tuneability of nonlinear composite materials strongly depends on the microgeometry and microtopology of the material and, in general, cannot be described in terms of volume fraction of components of composite material. In the designs presented, the increased tuneability is due to concentration of the high electric field in narrow regions with carefully selected geometry. The problem of loss in ferroelectric–dielectric composite materials is discussed. In the general case, the loss tangent stays between that of the components of the composite. For high-contrast ferroelectric–dielectric composite materials, the effective loss tangent is practically equal to the loss tangent of the ferroelectric.     

Interfacial adhesion of lignocellulosic materials in polymer composites: an overview

Cellulosic materials have long been used as cost-cutting fillers in the plastic industry. Among the various factors which determine the final performance of the composite materials depend, to a large extent, on the adhesion between the polymer matrix and the reinforcements, and, therefore, on the quality of the interface. In fact, the majority of cellulosic raw materials are lignocellulosics of different polarity to plastics, and due to this divergent behavior, the adhesion between cellulosic materials and polymer matrices is very poor. However, a sufficient degree of interaction or adhesion between the surface of the cellulosic materials and matrix resin is usually desired to achieve an optimum performance of the end-product. In many cases surface modification of the cellulosics or the matrix resins, using various additives, vinyl monomers, or coupling agents, are considered to be essential to achieve this goal. The present paper surveys research work published in this field with special emphasis on the cellulosic materials' surface chemistry, morphology, as well as interfacial properties of the composites in order to elucidate the role of surface treatments. In order to elucidate the mechanism of interaction on molecular level, it is necessary to employ various techniques, such as spectroscopy that can measure surface events. In fact, the complexity of the interphase region requires a variety of characterization methods for the thorough understanding of the physical and chemical nature of this region. Moreover, a proper combination of different techniques is necessary to provide a true picture of the interphase.     

Dynamical anisotropic magnetoelectric effects at ferroelectric/ferromagnetic insulator interfaces

The interfacial magnetoelectric interaction originating from multi-orbital hopping processes with ferroelectricassociated vector potential is theoretically investigated for complex-oxide composite structures.Large mismatch in the electrical permittivity of the ferroelectric and ferromagnetic materials gives rise to giant anisotropic magnetoelectric effects at their interface.Our study reveals a strong linear dynamic magnetoelectric coupling which genuinely results in electric control of magnetic susceptibility.The constitutive conditions for negative refractive index of multiferroic composites are determined by the analysis of light propagation.     

Optical properties of (nanometer MCM-41)-(malachite green) composite materials

Nanosized materials loaded with organic dyes are of interest with respect to novel optical applications. The optical properties of malachite green (MG) in MCM-41 are considerably influenced by the limited nanoporous channels of nanometer MCM-41. Nanometer MCM-41 was synthesized by tetraethyl orthosilicate (TEOS) as the source of silica and cetyltrimethylammonium bromide (CTMAB) as the template. The liquid-phase grafting method has been employed for incorporation of the malachite green molecules into the channels of nanometer MCM-41. A comparative study has been carried out on the adsorption of the malachite green into modified MCM-41 and unmodified MCM-41. The modified MCM-41 was synthesized using a silylation reagent, trimethychlorosilane (TMSCl), which functionalized the surface of nanometer MCM-41 for proper host-guest interaction. The prepared (nanometer MCM-41)-MG samples have been studied by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, low-temperature nitrogen adsorption-desorption technique at 77 K, Raman spectra and luminescence studies. In the prepared (nanometer MCM-41)-MG composite materials, the frameworks of the host molecular sieve were kept intact and the MG located inside the pores of MCM-41. Compared with the MG, it is found that the prepared composite materials perform a considerable luminescence. The excitation and emission spectra of MG in both modified MCM-41 and unmodified MCM-41 were examined to explore the structural effects on the optical properties of MG. The results of luminescence spectra indicated that the MG molecules existed in monomer form within MCM-41. However, the luminescent intensity of MG incorporated in the modified MCM-41 are higher than that of MG encapsulated in unmodified MCM-41, which may be due to the anchored methyl groups on the channels of the nanometer MCM-41 and the strong host-guest interactions. The steric effect from the pore size of the host materials is significant. Raman spectra firmly demonstrated the stable form obtained after the MG incorporation into the nanometer MCM-41. Therefore, nanometer MCM-41 appears to have a good potential for its use as a support for dyes and the (nanometer MCM-41)-MG composite materials may give a wide optical application.     

Application of Bruggeman and Maxwell Garnett homogenization formalisms to random composite materials containing dimers

The homogenization of a composite material comprising three isotropic dielectric materials was investigated. The component materials were randomly distributed as spherical particles, with the particles of two of the component materials being coupled to form dimers. The Bruggeman and Maxwell Garnett formalisms were developed to estimate the permittivity dyadic of the homogenized composite material (HCM), under the quasi-electrostatic approximation. Both randomly oriented and identically oriented dimers were accommodated; in the former case the HCM is isotropic, whereas in the latter case the HCM is uniaxial. Representative numerical results for composite materials containing dielectric–dielectric dimers demonstrate close agreement between the estimates delivered by the Bruggeman and Maxwell Garnett formalisms. For composite materials containing metal–dielectric dimers and metal–metal dimers with moderate degrees of dissipation, the estimates of the two formalisms are in broad agreement, provided that the dimer volume fractions are relatively low. In general, the effects of intradimer coupling on the estimates of the HCM’s permittivity are relatively modest but not insignificant, these effects being pronounced by anisotropy when all dimers are identically oriented.     

基于傅里叶红外光谱的SiO_2基相变储湿复合材料结构分析及性能优选预测

以SiO_2为载体材料、脂肪酸为相变材料制备具有相变调温性能与储湿调湿性能的SiO_2基相变储湿复合材料。采用等温吸放湿法和步冷曲线法测试不同脂肪酸用量的SiO_2基相变储湿复合材料相变调温性能与储湿调湿性能。利用傅里叶红外光谱测试SiO_2基相变储湿复合材料的结构组成,分析SiO_2与脂肪酸的嵌合机理。以SiO_2基相变储湿复合材料的傅里叶红外光谱特征吸收峰作为输入层,以SiO_2基相变储湿复合材料的脂肪酸用量、相对湿度52.89%下SiO_2基相变储湿复合材料吸湿平衡含湿量与放湿平衡含湿量的平均值、SiO_2基相变储湿复合材料从30~15℃降温所需的时间作为输出层,以S型激活函数作为隐含层,利用BE神经网络建立结构参数与综合相变储湿性能的SiO_2基相变储湿复合材料性能优选预测模型。结果表明,SiO_2基相变储湿复合材料中SiO_2与脂肪酸仅为物理嵌合,未发生化学作用;当脂肪酸用量0.079 mol时,所制备的SiO_2基相变储湿复合材料具有最优的综合相变储湿性能,即在相对湿度52.89%下的吸湿平衡含湿量为0.132 3 g·g~(-1)、放湿平衡含湿量0.147 5 g·g~(-1)、平衡含湿量的平均值为0.139 9 g·g~(-1),从30~15℃降温所需的时间为1 305 s;SiO_2基相变储湿复合材料的性能优选预测模型吻合性较好,具有较高的精确度,其预测值与实测值的相对误差为-2.07%和2.45%,可以用于优选预测SiO_2基相变储湿复合材料的储湿调湿性能和相变调温性能。     

石墨烯/铝基复合材料在纳米压痕过程中位错与石墨烯相互作用机制的模拟研究

石墨烯因其优异的力学性能已成为增强金属基复合材料的理想增强体.然而,目前对石墨烯/金属基复合材料在纳米压痕过程中嵌入石墨烯与位错之间的相互作用仍不清晰.本文采用分子动力学模拟方法,对90°,45°和0°位向的石墨烯/铝基复合材料进行了纳米压痕模拟,研究了压痕加载和卸载过程中石墨烯/铝基复合材料的位错形核及演化,以获取不同位向的石墨烯与位错的相互作用机制,并分析其对塑性区的影响.研究发现,石墨烯可以有效阻碍位错运动,并且石墨烯会沿着位错滑移方向发生弹性变形.在纳米压痕过程中,位错与不同位向石墨烯之间的相互作用差异导致塑性区的变化趋势不同.研究结果表明,在石墨烯/铝基复合材料中,位向不同的石墨烯对位错阻碍强度和方式不同,且石墨烯位向为45°的复合材料的硬度高于其他模型.此外,石墨烯/铝基复合材料的位错线总长度的演化规律与石墨烯位向紧密相关.本文研究可为设计和制备高性能石墨烯/金属基复合材料提供一定的理论指导.