Interfacial structure and mechanical properties of MgLi matrix composites

The study on interfacial structure and tensile properties of MgLi matrix composites. The results showed that there was a clear interface between the MgLi matrix and SiC whiskers. Calculation of thermodynamics confirmed that the clear interface between the matrix and SiC whiskers may contribute to the low reactionary potential or the low reactionary dynamics. However, some SiC whiskers were attacked. As a result, SiC whiskers connected with matrix in {111} and formed 70.5° or 109.5° stages on the whiskers surface in {111} face. The reason was the lower interfacial energy of {111} face. Tensile test confirmed that the SiC_w /MgLiAl composites showed higher tensile strength and higher modulus compared with MgLi matrix. Moreover, the specific strength and specific modulus were also increased obviously.     

Influence of material processing and interface on the fiber fragmentation process in titanium matrix composites

The objective of this work is to study the effect of composite processing conditions on the nature of the fiber–matrix interface in titanium matrix composites and the resulting fragmentation behavior of the fiber. Titanium matrix, single fiber composites (SFCs) were fabricated by diffusion bonding and tensile tested along the fiber axis to determine their interfacial load transfer characteristics and the resulting fiber fragmentation behavior. Two different titanium alloys, Ti-6Al-4V (wt%) and Ti-14Al-21Nb (wt%), were used as matrix material with SiC (SCS-6) fibers as reinforcement. The tensile tests were conducted at ambient temperature and were continuously monitored by acoustic emission. It was observed that the Ti-6Al-4V/SCS-6 composite system exhibited a greater degree of fiber–matrix interfacial reaction, as well as a rougher interface, compared to Ti-14Al-21Nb/SCS-6 composites. Acoustic emissions during tensile testing showed that most of the fiber fractures in Ti-6Al-4V/SCS-6 occurred at strains below ～5% and the fragmentation ceased at ～10% strain corresponding to specimen necking. In contrast, the Ti-14Al-21Nb/SCS-6 composite deformed without necking and fiber fractures occurred throughout the plastic range until final fracture of the specimen at about 12% strain. The markedly different fragmentation characteristics of these two composites were attributed to differences in the fiber–matrix interfacial regions and matrix deformation behavior.     

Assessment of interface deformation and fracture in metal matrix composites under transverse loading conditions

The transverse properties of unidirectional metal matrix composites (MMCs) are dominated by the fiber/matrix interfacial properties, residual stresses and matrix mechanical response. In order to monitor and study, in situ, the failure of interfaces in titanium-based composites subjected to transverse loading conditions, an ultrasonic imaging technique has been developed. The interface was imaged ultrasonically and the change in ultrasonic amplitude with the transverse loading was monitored, indicating the sensitivity of the technique to fracture and deformation of interfaces. This change in amplitude has been explained in terms of the multiple reflection theory of ultrasonic waves. The multiple reflection theory enabled estimation of the interfacial deformation and debonding as a function of loading. The ultrasonic technique was also used in conjunction with finite element modeling in order to quantify the fiber/matrix interfacial transverse strength in situ in MMCs.     

Discontinuous basalt and glass fiber reinforced PP composites from textile prefabricates: effects of interfacial modification on the mechanical performance

Spun and blown basalt fibers and their PP matrix composites were investigated. The composites were manufactured by hot pressing technology from carded and needle punched prefabricate using PP fiber as matrix material. Glass and blown basalt fibers were treated with reaction product of maleic acid-anhydride and sunflower oil while spun basalt fibers had a surface coating of silane coupling agent. Fibers were investigated with tensile tests while composites were subjected to static and dynamic mechanical tests. The results show that blown basalt fibers have relatively poor mechanical properties, while spun basalt fibers are comparable with glass fibers regarding geometry and mechanical performance. The static and dynamic mechanical properties of glass and spun basalt fiber reinforced composites are similar and are higher than blown basalt fiber reinforced composites. Results were supported with SEM micrographs.     

Effect of interfacial debonding and matrix cracking on mechanical properties of multidirectional composites

In composites, debonding at the fiber–matrix interface and matrix cracking due to loading or residual stresses can effect the mechanical properties. Here three different architectures — 3-directional orthogonal, 3-directional 8-harness satin weave and 4-directional in-plane multidirectional composites — are investigated and their effective properties are determined for different volume fractions using unit cell modeling with appropriate periodic boundary conditions. A cohesive zone model (CZM) has been used to simulate the interfacial debonding, and an octahedral shear stress failure criterion is used for the matrix cracking. The debonding and matrix cracking have significant effect on the mechanical properties of the composite. As strain increases, debonding increases, which produces a significant reduction in all the moduli of the composite. In the presence of residual stresses, debonding and resulting deterioration in properties occurs at much lower strains. Debonding accompanied with matrix cracking leads to further deterioration in the properties. The interfacial strength has a significant effect on debonding initiation and mechanical properties in the absence of residual stresses, whereas, in the presence of residual stresses, there is no effect on mechanical properties. A comparison of predicted results with experimental results shows that, while the tensile moduli E ₁₁, E ₃₃and shear modulus G ₁₂ match well, the predicted shear modulus G ₁₃ is much lower.     

Fiber bias in nanoindentation of polymer matrix composites

Nanoindentations were performed in the near fiber region of the matrix of a polymer matrix composite to attempt to determine the nanomechanical properties of the interphase. A possible fiber bias effect was observed and this effect was confirmed by performing nanoindentations in both the presence and in the absence of fiber. Changes in experimentation by using lower loads (40 μN and 80 μN) reduced the fiber bias effect. Cutting the samples at an angle to the fiber axis was performed to try to further reduce the fiber bias effect. The experimental variations considerably reduced the fiber bias effect. Specifically, the combination of angled cutting and use of reduced loads eliminated the fiber bias effect at distances greater than 150 nm from the fiber.     

In situ observation of interfacial debonding process induced by matrix crack propagation in two-dimensional unidirectional model composites

Interfacial debonding behavior is studied for unidirectional fiber reinforced composites from both experimental and analytical viewpoints. A new type of two-dimensional unidirectional model composite is prepared using 10 boron fibers and transparent epoxy resin with two levels of interfacial strength. In situ observation of the internal mesoscopic fracture process is carried out using the single edge notched specimen under static loading. The matrix crack propagation, the interfacial debonding growth and the interaction between them are directly observed in detail. As a result, the interfacial debonding is clearly accelerated in specimens with weakly bonded fibers in comparison with those with strongly bonded fibers. Secondary, three-dimensional finite element analysis is carried out in order to reproduce the interfacial debonding behavior. The experimentally observed relation between the mesoscopic fracture process and the applied load is given as the boundary condition. We successfully evaluate the mode II interfacial debonding toughness and the effect of interfacial frictional shear stress on the apparent mode II energy release rate separately by employing the present model composite in combination with the finite element analysis. The true mode II interfacial debonding toughness for weaker interface is about 0.4 times as high as that for a stronger interface. The effect of the interfacial frictional shear stress on the apparent mode II energy release rate for the weak interface is about 0.07 times as high as that for the strong interface. The interfacial frictional shear stress and the coefficient of friction for weak interface are calculated as 0.25 and 0.4 times as high as those for strong interface, respectively.     

Effect of Fiber Surface Modification on the Interfacial and Mechanical Properties of Kenaf Fiber-Reinforced Thermoplastic and Thermosetting Polymer Composites

The surfaces of kenaf fibers were treated with three different silane coupling agents. 3-glycidoxypropyltrimethoxy silane (GPS), 3-aminopropyltriethoxy silane (APS), and 3-methacryloxypropyltrimethoxy silane (MPS). Among them, the most effective one for the property improvement was GPS when it was applied to the kenaf fiber surfaces at 0.5 wt%. Thermoplastic polypropylene (PP) and thermosetting unsaturated polyester (UPE) matrix composites with chopped kenaf fibers untreated and treated at different GPS concentrations from 0.1 wt% to 5 wt% were fabricated using compression molding technique. The present study demonstrates that the interfacial, flexural, tensile, and dynamic mechanical properties of both kenaf/PP and kenaf/UPE composites importantly depend on the GPS treatments done at different concentrations. The greatest property improvement of both thermoplastic and thermosetting polymer composites was obtained with the silane treatment at 0.5 wt% and the mechanical properties were comparable with E-glass composites prepared the same polymer matrix under the corresponding fiber length and fiber loading. The results also agreed with each other with regard to their interfacial shear strength, flexural properties, tensile properties, storage modulus, with support of fracture surfaces of the composites.     

Effect of Geometry,Loading and Elastic Moduli on Critical Parameters in a Nanoindentation Test in Polymeric Matrix Composites with a Nonhomogeneous Interphase

Fiber nanoindentation models are developed for polymeric matrix composites with nonhomogeneous interphases. Using design of experiments, the effects of geometry, loading and material parameters on the critical parameters of the indentation test such as the load–displacement curve, the maximum interfacial shear and normal stresses are studied. The sensitivity analysis shows that the initial load–displacement curve is dependent only on the indenter type, and not on parameters such as fiber volume fraction, interphase type, thickness of interphase, and boundary conditions. The interfacial tensile radial stresses are not sensitive to indenter type, or to type and thickness of interphase, while the interfacial compressive radial stresses are sensitive mainly to boundary conditions and thickness of interphase; however, the influence of these factors on the interfacial radial stresses can be large. In contrast, the interfacial shear stress is sensitive to all factors, but the influence of the factors is relatively small.     

Influence of chemical treatments on the interfacial adhesion between sisal fibre and different biodegradable polymers

The influence of chemical treatments on the interfacial adhesion of sisal fibres and biodegradable matrices were studied in the present work. For that purpose, four different polymers were used: polycaprolactone (PCL), cellulose acetate, MaterBi Z (a commercial starch/polycaprolactone blend) and MaterBi Y (a commercial starch/cellulose derivatives blend). Alkaline and acetylation treatments were performed on sisal fibres. Properties were determined by means of tensile tests, adhesion measurements and contact angle determination. The interfacial shear strength was correlated with the hydrophilic character of the material.     

Roles of interfaces between carbon fibers and epoxy matrix on interlaminar fracture toughness of composites

The effect of atmospheric-pressure plasma treatment on high strength PAN-based carbon fibers had been studied in terms of fiber surface energetics and mode I and II interlaminar fracture toughness of unidirectional carbon fibers/epoxy matrix composites. The surface characterization of plasma treated carbon fibers was investigated by X-ray photoelectron spectroscopy (XPS) and contact angles. As a result, the plasma treatment changed the surface properties of the carbon fibers, mainly through formation of oxygen functional groups like hydroxyl, carbonyl, and carboxyl groups. According to contact angle measurements, it was observed that plasma treatment led to an increase in surface free energy of the fibers, mainly due to the increase of its specific component. Fracture toughness test results employing double-cantilever beam (DCB) and end notched flexure (ENF) specimens also showed that the increase in specific components or hydrogen bonding between the –OH groups on carbon fibers and the =O ring in epoxy matrix resins played an important role in improving the degree of adhesion at interfaces, resulting in an increase in the interfacial fracture toughness of the composites studied.     

Atomic structures and electronic properties of interfaces between aluminum and carbides/nitrides: A first-principles study

We perform a first-principles investigation of the atomic structures and electronic properties of interfaces between aluminum and four kinds of ceramics, TiC, TiN, VC and VN, under three orientations (001), (110) and (111). We find that the stable interfaces are those with bonding between Al atom and metalloid C (or N) atom, which is attributed to the overlap of p states of Al and d states of metalloid atoms at Femi level forming covalent components. Among the interfaces with the three orientations, the (111) interfaces are found to possess the largest adhesion energy in that the stacking of atoms follows intrinsic atomic distribution and this interfacial bonding is relatively strong. It is also found that the interfaces between Al and metal carbides (TiC and VC) are more stable than those between Al and metal nitrides (TiN and VN).     

A study of advances in characterization of interfaces and fiber surfaces in lignocellulosic fiber-reinforced composites

This article deals with the aspects of interfacial and surface characterization of natural fibers and their composites. Vegetable fibers and their composites have attracted the attention of scientists worldwide because of their favorable properties. The different chemical modifications of natural fibers and characterization aspects have been discussed. The adhesion between fiber and matrix is a major factor in determining the response of the interface and its integrity under stress. Therefore characterization of the interface is of utmost importance. Both fiber surface and polymer matrix surface can be modified to obtain a strong interface. Various treatments being used for the lignocellulosic surfaces and the characterization techniques have been illustrated. The four main techniques of interfacial characterization that are enumerated in this article are the micromechanical techniques, spectroscopic, microscopic and swelling techniques. The micromechanical techniques like fiber pull-out and fragmentation have been dealt with giving emphasis to experimental aspects. Recent studies dealing with interfacial study of different lignocellulosic fiber reinforced composites have also been cited.     

Ultrasonic study on binary liquid mixtures between some bromoalkanes and hydrocarbons

Densities and ultrasound velocities for the binary mixtures of 1-bromobutane+benzene and 1,4-dimethylbenzene and of 1-bromopentane+cyclohexane and benzene have been measured at 308.15 K. Adiabatic compressibilities (beta(ad)), and Wada's constants (W) have also been evaluated as a function of composition. The ultrasound velocities decrease, attains a minimum and then increase with increase in mole fractions of hydrocarbons in the binary mixtures except in the case of 1-bromopentane+benzene binary mixtures where the variation is just the reverse. Dependence of adiabatic compressibilities with mole fractions of hydrocarbons is sigmoid. The non-ideal behaviour of the systems studied is explained on the basis of dipole-induced dipole interactions.     

A study on the solubility and distribution of carbon in oxides

Measurements of radiocarbon in oxides were conducted after annealing single crystalline und polycrystalline FeO, Fe₃O₄, MnO, MgO, Cr₂O₃ and Al₂O₃ in radioactive CO₂-CO mixtures at 1000°C for different times. Concentrations of ≥ 0.01 wt. ppm C could be detected by anticoincidence counting and the distribution was observed by autoradiography. The measurements showed no carbon (< 0.01 ppm) in the lattice or the grain boundaries of pore- and crack-free oxides, carbon was detected only in cracks, pores or in grain boundaries which had cracked open. Thus, there is no measurable solubility of carbon in the bulk oxides for all the different chemical compositions investigated. Permeation of carbon through oxide layers on metals and alloys can only occur by transport of carbon-bearing molecules through cracks and pores of the oxide.     

Spatial charge distribution and conductivities of the LaAlO3/SrTiO3 interfaces: A theoretical study

The electronic properties of the charge carriers at the LaAlO₃/SrTiO₃ interfaces are investigated by first principles studies. For the n-type interface, the carriers are located only on the SrTiO₃ side. For the p-type interface, the carriers are highly localized at the interface. A critical thickness of the LaAlO₃ overlayer exists, below which, the interface is insulating. Moreover, we show that the effective masses and mobilities of the carriers are spatially anisotropic and have a strong disparity for the two types of carriers. These results are consistent with experimental observations and are explained by the band structures and alignments of the consisting oxides and their interaction at the interfaces.     

铝合金板疲劳微裂纹超声红外成像检测的数值及实验研究

超声红外成像检测技术是一种发展迅速的新型无损检测技术,可用于检测材料表面或近表面的缺陷,由于对缺陷具有选择性加热的特点,近年来备受检测行业的关注。该文在铝合金板中制作疲劳微裂纹,在板中激励声波,裂纹表面因振动摩擦生热,用红外摄像仪记录板表面温度分布。拍摄的红外图像序列经傅里叶变换后得到的幅值和相位图能清晰显示裂纹的特征,测量到的裂纹长度误差达到4.3%。用有限元模拟超声在板中裂纹处的生热过程,研究板中超声在裂纹处的励热机制。超声激励时间、裂纹表面间摩擦系数和裂纹开口宽度直接影响裂纹处的励热效果,最高温度通常位于裂纹尖端附近。模拟和实验结果均表明超声红外成像检测技术能对板中疲劳微裂纹实现快速检测,提供有效、可信的检测结果。     

Effects of urban morphology on the traffic noise distribution through noise mapping: A comparative study between UK and China

Due to the rapid urban development and massive population increase in many eastern cities, the difference in urban density and morphology between typical western and eastern cities is becoming significant. This consequently makes the noise distribution in the eastern cities rather different from typical low density European cities. In this research, two representative cities with different urban densities, Greater Manchester in the UK and Wuhan in China, were selected, which have low and high average urban density respectively, and also have considerable differences in building form and traffic pattern. In the mean time, these two cities have similar urban scale and traffic amount. In each city, based on the urban morphological analyses considering urban land-use, building and road density, and noise source distribution, a number of typical urban areas, 500 * 500 m² each, were sampled. A noise-mapping software package was then used to generate generic noise maps, based on existing digital vector maps for terrain and building, and traffic data obtained by on-site measurements. The comparison results show that the average and minimum noise level in Greater Manchester samples is generally higher than that in Wuhan samples, while the maximum noise level in Wuhan samples is mostly higher. By developing a Matlab program, correlations have been analysed between noise distributions and the urban characteristics relating to urban density, such as the road and building coverage ratio. Overall, comparisons between these two typical cities have shown significant effects of urban morphology on the traffic noise distribution.     

Mechanisms of interaction between luteolin and the catalytic zinc ion in matrix metalloproteinases: a computational study

Many experimental studies have found that flavonoids including luteolin can inhibit the activities of matrix metalloproteinases (MMPs), but the related theoretical studies are rather lacking. In this paper, we perform PM6 quantum chemistry calculations together with modeling of ligand‐water exchange reactions to investigate the mechanisms of interaction between luteolin and catalytic zinc ion in MMPs. The calculations show that the electron transfer from the luteolin molecule to the catalytic zinc ion in MMPs occurs when the catalytic zinc ion coordinates with the O atoms of substituent groups at various positions of A, B, and C rings of luteolin molecule. It is found that the more the number of the electron transfer from one coordinating O atom of substituent groups of luteolin molecule to the catalytic zinc ion, the stronger the coordinating ability between them. We further find that comparing with the O atoms of hydroxy groups at 5‐, 7‐, 3′‐, and 4′‐positions of luteolin molecule, the coordinating ability for the O atom of carbonyl group at its 4‐position with the catalytic zinc ion is the strongest, which indicates that when luteolin inhibits MMPs activity, the catalytic zinc ion should coordinate with the carbonyl group at 4‐position of luteolin molecule, rather than the hydroxy groups at its other positions, in agreement with the relevant experimental results reported in previous literature. This paper may be helpful for designing the new MMPs inhibitors having higher biological activities by carrying out the structural modifications of luteolin molecule. Copyright © 2012 John Wiley & Sons, Ltd.     

A study on the DC-electrical and thermal conductivities of epoxy/ZnO composites doped with carbon black

Thermo-electrical characterizations of hybrid polymer composites, made of epoxy matrix filled with various zinc oxide (ZnO) concentrations (0, 4.9, 9.9, 14.9, and 19.9 wt%), and reinforced with conductive carbon black (CB) nanoparticles (0.1 wt%), have been investigated as a function of ZnO concentration and temperature. Both the measured DC-electrical and thermal conductivities showed ZnO concentration and temperature dependencies. Increasing the temperature and filler concentrations were reflected in a negative temperature coefficient of resistivity and enhancement of the electrical conductivity as well. The observed increase in the DC conductivity and decrease in the determined activation energy were explained based on the concept of existing paths and connections between the ZnO particles and the conductive CB nanoparticles. Alteration of ZnO concentration with a fixed content of CB nanoparticles and/or temperature was found to be crucial in the thermal conductivity behavior. The addition of CB nanoparticles to the epoxy/ZnO matrix was found to enhance the electrical conduction resulting from the electronic and impurity contributions. Also, the thermal conductivity enhancement was mostly attributed to the heat transferred by phonons and electrons hopping to higher energy levels throughout the thermal processes. Scanning electron microscopy and energy-dispersive spectroscopy were used to observe the morphology and elements’ distribution in the composites. The observed thermal conductivity behavior was found to correlate well with that of the DC-electrical conductivity as a function of the ZnO content. The overall enhancements in both the measured DC- and thermal conductivities of the prepared hybrid composites are mainly produced through mutual interactions between the filling conductive particles and also from electrons tunneling in the composite's bulk as well.