Effect of high rate deformation induced precipitation hardening on the failure of aluminium rivets

Aluminium alloy (7050-T73) rivets were fabricated by an electromagnetic riveting process. Each rivet was formed in less than 500sec. Microcracks and severely deformed regions were observed in the rivet head. Microprobe analysis, optical and scanning electron microscopic examination on the rivets did not yield conclusive evidence that the microcracks were caused by impurities such as iron and silicon. The data obtained in this study support the view that heat generated by material flow at high speed in the rivet head induced precipitation hardening. The precipitation hardening significantly increased the material hardness in the severely deformed shear zone. It Is believed that the increment of hardness in the shear zone of the rivets fabricated from the slugs which were previously age hardened resulted in a further decrease in ductility. Hence the initiation of voids which subsequently coalesced to form microcracks in the shear zone.     

Intensification of convective heat exchange in anomalously viscous media by the application of artificial periodic roughness

The results of an experimental investigation of the intensification of convective heat exchange in the flow of anomalously viscous liquids in pipes with artificial periodic roughness are presented. An estimate is made of the thermohydrodynamic efficiency of the application of this means of intensification to anomalously viscous media.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 36, No. 1, pp. 26–31, January, 1979.     

Effect of crystallographic texture on precipitation induced anisotropy in an aluminium magnesium silicon alloy

The effect of crystallographic texture on precipitation induced anisotropy in yield strength of an aluminium magnesium silicon alloy was investigated. Solutionized samples were subjected to unidirectional and multi-step cross rolling to yield distinct crystallographic textures in the Al–Mg–Si alloy. The rolled sheets were then subjected to annealing followed by second solutionizing treatment to provide sheets with similar grain size and dislocation content but distinct texture. Ageing experiments were carried out on these sheets at 443 K for different time intervals. It was observed that the evolution of anisotropy in yield strength of the age hardened alloy depends on texture. The difference in age hardening response brought about by varying initial texture controls the evolution of anisotropy in mechanical properties of the alloy. This was manifested in terms of transition from anisotropic to isotropic mechanical properties in the unidirectionally rolled samples after peak ageing. On the contrary, a transition from isotropic to anisotropic yield behaviour was observed for multi-step cross rolled samples. This is attributed to enhanced precipitation hardening in crystallographically softer orientations compared to crystallographically harder orientations.     

Finite element analysis of viscoelastic solids responding to periodic disturbances

A finite element analysis for viscoelastic solids responding to periodic disturbances travelling at constant speed is developed. The disturbance is decomposed into harmonic components using the Discrete Fourier Series, and the viscoelastic material response is determined using the Correspondence principle. The procedure is used to solve two and three dimensional contact problems to demonstrate its effectiveness.     

Effect of thermal instability on the rate of convective heat transfer

Results are shown of an experimental study concerning the transient convective heat transfer in the housing clearance in a turbine model.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 3, pp. 514–518, September, 1972.     

Measurement of temperature distributions in a convective flow induced by powerful optical radiation

Results are presented from an experimental study of the convection which occurs within a liquid upon heating by a powerful light beam. The dependence of temperature on the convective jet axis upon power of the heating radiation is obtained.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 6, pp. 980–982, June, 1988.     

Fluctuating flow induced by periodic suction through a rotating disk

Summary This paper is concerned with the time-harmonic and time-mean flow induced by a normal periodic suction through a disk rotating in contact with an incompressible viscous fluid. Two separate analytical-numerical solutions are developed for the extreme cases of low and high frequency oscillations, employing the Fettis-Benton method. General formulae for the skin-friction components and the far-field suction velocity are obtained. The deduced quasi-steady results are in agreement with the available numerical results.

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Die durch periodisches Saugen durch eine rotierende Scheibe erzeugte schwankende Strömung

Zusammenfassung Die vorliegende Arbeit behandelt die zeitlich harmonische und die zeitlich gemittelte Strömung, verursacht durch eine periodische Saugwirkung normal durch eine Scheibe, die in einer inkompressiblen zähen Flüssigkeit rotiert. Zwei getrennte analytisch-numerische Lösungen werden mit Hilfe der Fettis-Benton-Methode für die beiden Sonderfälle niedriger bzw. hoher Oszillationsfrequenz hergeleitet. Allgemeine Beziehungen ergeben sich für die Komponenten der Oberflächenreibungskraft und die Sauggeschwindigkeit. Die Ergebnisse für den stationären Fall sind in Übereinstimmung mit numerisch gewonnenen Resultaten.

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On leave from Indian Institute of Technology Kharagpur India     

Effect of free convective heat transfer on the temperature state of superconductors

The article investigates the temperature state of a rigid-type coaxial superconductor when the space of the inner core is filled with stagnant helium.     

Nonlinear study of convective heat transfer and fluid flows induced by travelling thermal waves

Summary A nonlinear study is made of the convective heat transfer and the fluid flow in an incompressible viscous fluid confined to a vertical wavy channel in four different geometrical configurations. The flow is generated by the periodic thermal waves prescribed at the wavy walls of the channel. The problem is solved by a perturbation technique with the assumption that the solution consists of a mean part and a perturbed part. The mean, perturbed and the total solutions are numerically evaluated for various values of the physical parameters involved in the problem. The mean solution is found to be in good agreement with that obtained by Vajravelu and Sastri [4]. The perturbed part of the solution is made of the contributions from the waviness of the channel walls and the travelling thermal waves. Of all the parameters, the heat source parameter plays an important role in augmenting (diminishing) the skin friction (the heat transfer) at the wally=1. Several interesting properties of the flow field and the heat transfer are discussed. The results of this analysis are also graphically presented.With 12 Figures     

Effect of pH on the precipitation of hydroxyapatite on silica gels

Silica-HAp composites have been produced with particle size ranging from several nm to few μm, through control of the pH of the solution, which also controls morphology. A calcium ions reservoir has been made available as a Ca/EDTA soluble complex allowing the production of HAp at low temperature and short periods of time (hours). The presence of silica seems to promote the formation of HAp under these conditions. Electronic Publication     

Effect of precipitation route on the properties of antimony trioxide

Antimony trioxide was prepared, using antimony potassium tartarate as starting material, via forward and reverse precipitation technique. The characteristics of the resulting antimony oxides were determined by BET surface area method, differential thermogravimetry analysis (DTG), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and SEM. The DTG curves for all uncalcined samples showed only a single endothermic peak which indicated that the sample is antimony trioxide. Unlike forward precipitation technique which resulted in a single antimony trioxide phase which is senarmontite, reverse precipitation technique produced antimony trioxide with both senarmontite and valentinite phase. Upon calcinations at 723 K, a small amount of Sb₂O₄ with cervantite phase was formed at the expense of Sb₂O₃ senarmontite phase as detected from the XRD pattern and infrared spectrum of RSb. The effect of preparation route on the properties of the antimony trioxide produced was clearly demonstrated.     

Direct precipitation of silver nanoparticles induced by a high repetition femtosecond laser

Silver nanoparticles were precipitated directly in Ag⁺ doped silicate glass by a 150 fs, 800 nm, 250 kHz femtosecond laser irradiation. The irradiated pattern turned to yellow without heat treatment. The absorption peak about 400 nm, ascribed to the surface plasmon resonance of the formed silver nanoparticles, was observed. We believe that the reduced Ag atoms, via capturing free electrons created by multi-photon process, may aggregate into the Ag nanoparticles due to femtosecond laser inducing heat accumulation effect. This result has promising applications for the fabrication of 3D multi-colored images inside a transparent material.     

Effect of sintering temperature on the properties of Cu-Co ferrites prepared by oxalate precipitation method

Polycrystalline Cu-Co ferrite powder was synthesized following oxalate precipitation method. The samples of the compound Cu_0.5Co_0.5Fe₂O₄ were heated at different temperatures in the range of 773-1173 K and were characterized by X-ray diffraction and SEM techniques. The results of XRD show the formation of single-phase cubic spinel structure. The lattice parameter showed a minimum value for the sample heated at 1073 K. It has been observed that grain size increases with the increase in temperature and is maximum (3.2 μm) for the powder sintered at 1173 K.     

The effect of electrically induced convection in dielectric liquids on convective heat transfer

The paper deals with the possibility of controlling convective heat transfer in a dielectric liquid by way of imposition of an electric field on the system. Two-dimensional numerical simulation is used to analyze the effect of a nonuniform electric field on the structure of convective motions and on the effectiveness of convective heat transfer. The possibility is studied of enhancement of convective heat transfer with deionized water and liquid nitrogen used as working liquids.     

Axisymmetric free convection induced by periodic variation in the temperature of a horizontal plane surface

Axisymmetric free convection flow of a viscous incompressible fluid above a horizontal plane surface is analysed when the temperature of the plane surface oscillates about a non-zero mean. The solution of the multilayered model is obtained by matching the inner and the outer asymptotic expansions. It is found that the order of the mean induced flow is larger than that of the order of the applied mean temperature. Specific series expansions are obtained for the skin-friction and the heat-transfer at the horizontal surface. Estimates of the physical parameters yielding stable fluid motion are derived.     

Effect of lanthanum on the precipitation of NbC in bcc Fe

The effect of lanthanum on the precipitation of NbC in bcc Fe has been investigated by the first-principles calculations in combination with the experiments. The interactions of La–C are repulsive in the first-, second- and third-nearest-neighbour configurations, and the binding energies of La with Nb were predicted to be positive, and converge to a weak value. The addition of La decreases the solubility of C (above 763?K) and Nb, and increases the chemical potential of these two solutes, thus promoting the precipitation of NbC in bcc Fe. The experimental results show that the La-contained Nb-bearing steel has a relatively faster precipitation rate of NbC than the La-free steel, during isothermal treatment in ferritic region.     

Effect of DTPA on the nephrotoxicity induced by uranium in the rat

The only treatment proposed after human contamination with MOX (mixed oxide of uranium and plutonium) is diethylenetriaminepentaacetic acid (DTPA), because plutonium is considered to be the major risk. However, both DTPA and uranium are nephrotoxic at high dosages and DTPA has been shown to increase in vitro the cytotoxicity induced by uranium on cultured epithelial tubular cells. This work aimed to test this effect in vivo. Rats were injected with subtoxic (57 microg kg(-1)) to toxic (639 microg kg(-1)) amounts of uranium as nitrate at 0 h, they received two DTPA injections (30 micromol kg(-1)) at 2 min and 24 h and were euthanased at 48 h. The nephrotoxic effects were evaluated by measurement of the body weight gain, food and water intake, measurement of biochemical parameters in urine and blood, and histological examination of one kidney. The main result was that DTPA did not increase the nephrotoxicity induced by uranium in the range of concentrations tested, which was inconsistent with the in vitro results.     

Effect of annealing temperature on the energy transfer in Eu-doped ZnO nanoparticles by chemical precipitation method

Eu-doped ZnO nanoparticles were synthesized by the chemical precipitation method and the annealing temperature effect on the structures and photoluminescence (PL) properties of the nanoparticles were briefly investigated. The X-ray diffraction and energy dispersive spectroscopy results indicated that the Eu³⁺ was successfully incorporated into the crystal lattice of ZnO host when the annealing temperature was fixed at 400 °C, but the Eu³⁺ ions were partly precipitated from the host with the annealing temperature increasing. The as-obtained ZnO: Eu nanocrystals composed of nanoparticles had an average size of 10 nm, and the valence states of europium ions in the nanocrystals were determined as tervalent. PL spectroscopy indicated that the characteristic red emissions of Eu³⁺ ions were attributed to the ⁵D₀ → ⁷F₀, ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions, respectively. Moreover, the annealing temperature was found to have effect on the red emission of Eu³⁺ ions. That is to say, the energy transfer in the doped nanocrystals could be adjusted by different annealing temperatures.