Micromechanical analysis of fuzzy fiber reinforced composites

A novel fuzzy fiber reinforced composite (FFRC) reinforced with zig-zag single-walled carbon nanotubes (CNTs) and carbon fibers is proposed. The distinct constructional feature of this composite is that the uniformly aligned CNTs are radially grown on the surface of carbon fibers. Analytical models based on the mechanics of materials approach and the Mori–Tanaka method are derived to estimate the effective elastic constants of this proposed FFRC. The values of the effective elastic properties of this composite are estimated with and without considering an interphase between the CNT and the polymer matrix. It has been found that the transverse effective properties of this composite are significantly improved due to the radial growing of CNTs on the surface of carbon fiber. The effective properties are also found to be sensitive to the CNT diameter.     

On the optical and electrical properties of rf and a.c. plasma polymerized aniline thin films

Polyaniline is a widely studied conducting polymer and is a useful material in its bulk and thin film form for many applications, because of its excellent optical and electrical properties. Pristine and iodine doped polyaniline thin films were prepared by a.c. and rf plasma polymerization techniques separately for the comparison of their optical and electrical properties. Doping of iodine was effectedin situ. The structural properties of these films were evaluated by FTIR spectroscopy and the optical band gap was estimated from UV-vis-NIR measurements. Comparative studies on the structural, optical and electrical properties of a.c. and rf polymerization are presented here. It has been found that the optical band gap of the polyaniline thin films prepared by rf and a.c. plasma polymerization techniques differ considerably and the band gap is further reduced byin situ doping of iodine. The electrical conductivity measurements on these films show a higher value of electrical conductivity in the case of rf plasma polymerized thin films when compared to the a.c. plasma polymerized films. Also, it is found that the iodine doping enhanced conductivity of the polymer thin films considerably. The results are compared and correlated and have been explained with respect to the different structures adopted under these two preparation techniques.     

Vortex Mutual Friction in Superfluid 3He

We give a full account of our extensive measurements of vortex mutual friction in rotating superfluid ³He, in both the A- and B-phases. The B-phase results are in qualitative agreement with a theory based on the concept of “spectral flow”; the agreement becomes quantitative if an effective energy gap of 0.63 Δ is used, but the Justification for such a substitution is not clear. The vortex core transition, at first not seen because of metastability and hysteresis, has now been observed. Detailed investigation suggests that the high temperature vortex state is a temperature dependent mixture of at least two vortex types. The A-phase mutual friction is found to be well described by two hydrodynamic coefficients, the orbital viscosity and the orbital inertia. The latter corresponds to an orbital angular momentum per Cooper pair of (0.0015 ± 0.0017 ) ħ, consistent with the prediction of the spectral flow theory. We find that the most uniform l texture is obtained by cooling through T_c while rotating, and then stopping rotation. Detailed investigation of textural memory effects shows that the uniform l-up and l-down textures are associated with opposite directions of rotation. We discuss the various types of texture that may be formed in our experiments. Finally, we compare our mutual friction results with those found in ⁴HeII.     

Bringing Engineering Research to Market: How Universities,Industry, and Government are Attempting to Solve the Problem

Abstract:

Significant barriers impede the effective commercialization of new technologies created at universities. We review the nature of these barriers and consider one solution in the form of a collaborative network environment: the National Network for Technology Entrepreneurship and Commercialization (N2TEC). This article contributes on two levels to the knowledge of engineering managers who are attempting to rapidly implement technology: (1) it explains an important new tool for facilitating collaboration and commercialization, and (2) it describes the challenges met and overcome in the organization and implementation of a virtual network.     

Theoretical study of Ti:LiNbO3 strip waveguides in the Mid-infrared

Abstract

The transverse magnetic and transverse electric mode size and effective refractive index as functions of the Ti-strip initial width W, diffusion temperature T and Ti-strip initial thickness H in c-cut Ti-diffused LiNbO₃ waveguides have been theoretically studied at wavelengths of 3.0 and 3.39 μm on the basis of modified expressions for the waveguide surface index increment. The single-mode, multiple-mode and cut-off conditions have been identified from those effective refractive index plots. These mid-infrared numerical results are discussed comparatively with near-infrared data reported earlier.     

Dynamic Effective Properties of Particle-Reinforced Composites with Viscoelastic Matrix

The frequency-dependent dynamic effective properties of the particle-reinforced composites with the viscoelastic matrix are studied. Several equations to predict the effective wavenumber of the coherent plane waves propagating through particle-reinforced composites are discussed and the equation given by Gubernatis, J.E., [‘Effects of microstructure on speed and attenuation of elastic waves in porous materials’, Wave Motion, 6, 1984, 579–589] based on the independent scattering approximation is used in this paper. The effective phase velocity, the effective attenuation and the effective elastic moduli are evaluated. Numerical calculations are carried out for two kinds of composites, namely, Lead-Epoxy and Glass-Epoxy and the numerical results show that the frequency-dependent dynamic effective properties are related to both the multiple scattering effects among the distributed particles and the viscous dissipative effects of the viscoelastic matrix. However, these effects in the composites with distributed heavy particles (lead) and light particles (glass) are of evidently different features.     

Structural characterization of vacuum evaporated ZnSe thin films

Thermally evaporated ZnSe thin films deposited on glass substrates within substrate temperatures (T _s)at 303 K-623 K are of polycrystalline nature having f.c.c. zincblende structure. The most preferential orientation is along [111] direction for all deposited films together with other abundant planes [220] and [311]. The lattice parameter, grain size, average internal stress, microstrain, dislocation density and degree of preferred orientation in the film are calculated and correlated with T _s.     

Mathematical model of extrusion preheater

Abstract

An effective numerical model has been developed to simulate the thermal behaviour of extrusion preheating processes for metals. The model utilises a finite difference scheme to predict the temperature profile of the billet during and subsequent to heating. The model is versatile and has been applied to show that a three zone induction preheater, especially designed to provide taper heating for isothermal extrusion, can achieve the desired taper temperature profile for aluminium alloys. Applications of the present model to other types of preheater are also discussed.

MST/399     

Recent progress in the development of solid catalysts for biomass conversion into high value-added chemicals

Abstract

In recent decades, the substitution of non-renewable fossil resources by renewable biomass as a sustainable feedstock has been extensively investigated for the manufacture of high value-added products such as biofuels, commodity chemicals, and new bio-based materials such as bioplastics. Numerous solid catalyst systems for the effective conversion of biomass feedstocks into value-added chemicals and fuels have been developed. Solid catalysts are classified into four main groups with respect to their structures and substrate activation properties: (a) micro- and mesoporous materials, (b) metal oxides, (c) supported metal catalysts, and (d) sulfonated polymers. This review article focuses on the activation of substrates and/or reagents on the basis of groups (a)–(d), and the corresponding reaction mechanisms. In addition, recent progress in chemocatalytic processes for the production of five industrially important products (5-hydroxymethylfurfural, lactic acid, glyceraldehyde, 1,3-dihydroxyacetone, and furan-2,5-dicarboxylic acid) as bio-based plastic monomers and their intermediates is comprehensively summarized.     

Amplification of Picosecond Pulses in Neodymium-doped Single-mode Optical Fibres

Abstract

The picosecond pulses from the output of a fibre-grating pair compressed mode-locked c.w. pumped Nd : YAG laser have been amplified in a neodymium-doped single mode optical fibre using a counter propagating c.w. pump geometry. Gains of up to times ten were measured in a 2·5 m fibre length for input signal energies of up to 0·2 pJ per pulse.     

Failure analysis on gas pressure formed spherical domes of Pb–Sn eutectic alloy

Abstract

This paper addresses the issue of instability of deformation during gas pressure forming of superplastic sheets. With regard to fracture strain, the plastic behaviour of the spherical dome has been described in terms of the local effective stress and the effective strain. These quantities are equated to the uniaxial stress state. The limiting effective thickness strain is obtained utilising the relations between the strain rate sensitivity index and the fracture strain. The results are found to be in good agreement with the measured failure strains.     

Dip-coated hydrotungstite thin films as humidity sensors

Thin films of a hydrated phase of tungsten oxide, viz. hydrotungstite, have been prepared on glass substrates by dipcoating method using ammonium tungstate precursor solution. X-ray diffraction shows the films to have a strongb — axis orientation. The resistance of the films is observed to be sensitive to the humidity content of the ambient, indicating possible applications of these films for humidity sensing. A homemade apparatus designed to measure the d.c. electrical resistance in response to exposure to controlled pulses of a sensing gas has been employed to evaluate the sensitivity of the hydrotungstite films towards humidity.     

Step Model of Erosion of Electrodes. III. Adaptation to Arbitrary Regimes of Electroerosion Treatment

The step model of erosion of the cold electrodes of electricarc heaters proposed in Inzh.Fiz. Zh., 76, No. 2, 36–42 (2003) and Ann. N.Y. Acad. Sci., 891, 36–42 (1999) has been modified for calculating the rate of electroerosion treatment of materials. The point heat source [J. Appl. Phys., 66, No. 9, 4095–4103 (1989)] for determining the effective enthalpy of erosion has been reduced to a plane surface heat source equivalent in erosion and corresponding to the step model. The approximation analytical relations in dimensionless numbers have been obtained. The calculation results are in satisfactory agreement with the experimental data of different authors.     

Study of lithium glassy solid electrolyte/electrode interface by impedance analysis

Cells of lithium ion conducting glassy electrolyte Li ₂SO₄-Li₂O-B₂O₃ with different combinations of electrodes (stainless steel blocking electrode, lithium non-blocking electrode and TiS₂ electrode) have been prepared. The a.c. impedance measurements of the cells have been studied at elevated temperature as a function of time. The circuit elements such as bulk resistance, double layer capacitance and charge transfer resistance have been inferred and their time dependence studied. The results show that the electrolyte and the interface are chemically very stable with the different types of electrodes studied here.     

Synthesis, characterization and conductivity studies of polypyrrole-fly ash composites

In situ polymerization of pyrrole was carried out in the presence of fly ash (FA) to synthesize polypyrrole-fly ash composites (PPy/FA) by chemical oxidation method. The PPy/FA composites have been synthesized with various compositions (10, 20, 30, 40 and 50 wt%) of fly ash in pyrrole. The surface morphology of these composites was studied with scanning electron micrograph (SEM). The polypyrrole-fly ash composites were also characterized by employing X-ray diffractometry (XRD) and infrared spectroscopy (IR). The a.c. conductivity behaviour has been investigated in the frequency range 10²–10⁶ Hz. The d.c. conductivity was studied in the temperature range from 40–200°C. The dimensions of fly ash in the matrix have a greater influence on the observed conductivity values. The results obtained for these composites are of greater scientific and technological interest.     

Kinetics of granulation of discontinuous phase in eutectic structures

Abstract

Useful properties of eutectic alloys have been found to relate to the presence of granulated discontinuous phase, and its formation is encouraged during solidification; although difficulties are encountered in some alloy systems. In the present paper it is suggested that discontinuous phase granulation can be achieved through either solidification processing or heat treatment. The kinetics of granulation during heat treatment and the factors affecting it have been analysed and examined for eutectic silicon in Al–Si alloys and for graphite in cast irons during heat treatment, using the techniques of high-temperature and quantitative metallography. The concept of combined control of the size and morphology of the discontinuous phase through solidification and heat treatment was developed.

MST/254     

Optical properties of lead-bismuth cuprous glasses

The optical transmission and absorption spectra in UV- VIS were recorded in the wavelength range 350–800 nm for different glass compositions in the system (CuO) _x (PbO) ₅₀−x(Bi₂O₃)₅₀ (x = 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 20.0). Absorption coefficient (α), optical energy gap (E_opt), refractive index (n_D), optical dielectric constant (ε′_∞), measure of extent of band tailing (ΔE), constant (β) and ratio of carrier concentration to the effective mass (N/m*) have been reported. The effects of compositions of glasses on these parameters have been discussed. It has been indicated that a small compositional modification of the glasses lead to an important change in all the optical properties including non-linear behaviour. The optical parameters were found to be almost the same for different glasses in the same family.     

Generation and Amplification of Subharmonics in Semiconductor-doped Glass by a Modulated Argon-ion Laser

Abstract

Subharmonic generation and amplification and nearly chaotic response has been observed in an optical light-by-light modulator based on the semiconductor-doped glass, Schott Glass OG530, pumped by a modulated c.w. argon-ion laser (λ = 514·5 nm).     

Preparation and characterization of Ag-added Bi1.84Pb0.4Sr2Ca2.2Cu3O10+x bulk tube conductors for cryogen free superconducting magnet

Bulk tube conductors of Bi _1.84 Pb _0.4 Sr ₂ Ca _2.2 Cu ₃ O _10+x with addition of silver varying from 0 to 25 wt% (not reported earlier) were systematically studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical transport and a.c. susceptibility techniques. The tube conductors formed by cold isostatic pressing (CIP) of the powders obtained from spray drying method have been made successfully. It was found that Ag addition has not only affected the formation of the desired Bi-2223 phase and the microstructure of these large bulk tube samples thereby influencing on the critical current ( I _c ),it also reduces the contact resistance to minimize the cryogen losses. These variations have been found to be Ag content dependent. An optimized value of 10 wt% Ag has been found to produce the best quality tubes showing reproducible I _c value > 120 Amp at 77 K which is in general a requirement to energies of the cryogen free conventional/HTSC superconducting magnets below 20 K.     

Effective anisotropic elastic constants of bimaterial interphases: comparison between experimental and analytical techniques

The effective elastic constants of a bimaterial composite were experimentally measured with the goal of validating the numerical predications of these constants made by homogenization theory. Secondly, solutions predicted by homogenization theory were compared to predictions made with more standard composite theories. Composite specimens consisting of titanium and epoxy were developed to mimic a porous titanium/tissue interphase. Tensile and shear tests (ASTM D3983) measured the stiffness along the porous coating/epoxy interphase (E _L), across the interphase (E _T) and in shear (G _LT). No significant differences in moduli were found between the experimental measurements and predictions made with homogenization theory, nor between the experimental measurements and Hashin-Shtrikman estimates. Homogenization theory predicted results usually within 20% of Hashin-Shtrikman estimates, but typically more than 50% different from what is predicted by the rule of mixtures. However, homogenization theory allows calculation of anisotropic stiffness estimates and local strains, neither of which is possible using Hashin-Shtrikman estimates. With this experimental validation, the accuracy of homogenization theory for use in implant/tissue interface mechanics applications is confirmed. Since the composite interphase is anisotropic and more compliant in the transverse direction, with stiffness an order of magnitude lower across the interphase, local mechanics, tissue ingrowth and remodeling may be strongly directional dependent.Department of Surgery, Orthopaedic Research LaboratoriesDepartment of Biologic and Materials Sciences, School of Dentistry