Effect of the Temperature Drop between the Isothermic Walls of a Channel on the Structure of Supersonic Flow and on the Aerodynamic Properties

The results of numerical analysis of the two-dimensional Navier–Stokes equations are used to investigate a supersonic flow of a perfect gas in a symmetric plane channel of variable cross section at the Mach number of M= 4 at the inlet for the Reynolds numbers in the range Re = 10³–10⁶. The top and bottom channel walls are assumed to be isothermic with different values of the temperature factor. It is shown that the asymmetry of the boundary conditions for temperature leads to the asymmetry of the entire flow field.     

Mechanical behaviour,percolation and damage of materials with viscous solid grain boundaries

The mechanical behaviour, percolation and damage mechanism of a aluminium alloy with viscous solid grain boundaries (GBs) at 465 °C have been characterized in experiments performed in tension or compression in the strain rate range of 10^–5-10^–2s^–1. It was found that grain-boundary sliding (GBS) occurs as strain rates below 10^–4s^–1. It was shown that the viscous solid interphase migrates during the process of deformation. In the case of tension, it was squeezed out of GBs parallel with the tension axis into GBs perpendicular to the axis and vice versa in the case of compression. This local percolation is discussed in terms of the viscosity of the interphase, gradient of local stresses and percolation time. The viscosity of the solid interphase is estimated. It was also found that cavitation depends on the type of stress (tension or compression) and the strain rate. Cavity nucleation occurs at multiple points when GBS happens or along G B facets in the absence of GBS. Cavity growth takes place along GBs at high normal stresses and the cavity coalsescence leads to saw-tooth fracture.     

Quasi-static and dynamic compression behaviour of an FPTM alumina-reinforced aluminium metal matrix composite

An aluminium metal matrix composite reinforced with continuous unidirectional -alumina fibres has been compression tested at quasi-static and dynamic strain rates. In the transverse direction, the composite showed increasing flow stress (at 5% strain) and maximum stress within the studied strain rates, 10^–3–3 × 10³ s^–1. In the longitudinal direction, the maximum stress of the composite increased similarly with increasing strain rates within the range 10^–5–7 × 10² s^–1. It is shown that, if brooming of the sample ends can be suppressed, the failure stress of the composite in longitudinal compression increases significantly. Metallographic observations reveal the typical modes of damage initiation in the composite.     

Behavior of Impurity Inclusions during Vacuum Distillation of Tellurium

Experimental data are presented on the effect of the Te evaporation rate on the efficiency of the removal of submicron carbon particles (major impurities in Te, present in amounts from 10⁶to 5 × 10⁸cm^–3, depending on the purification procedure). By distilling a small amount of the melt, the effective separation coefficient was determined as a function of particle size. For 0.065- to 0.14-m particles at a minimum evaporation rate of 3 × 10^–7cm³/(cm²s), the separation coefficient lies in the range 9–100. As the evaporation rate increases to 2.5 × 10^–5cm³/(cm²s), the separation coefficient drops to 2–8. Among the factors influencing the purification efficiency is the floating (inverse sedimentation) of submicron carbon particles in molten Te, observed experimentally upon long-term holding.     

Features of the effect of stress concentration on the fatigue resistance of graphitic steel with impact loading

A procedure and results of experimental studies are given for the fatigue resistance of smooth specimens and specimens with stress concentrators ( = 1.4 and 4.2) made of cast graphitic steel of different harness with impact loading. Discontinuities have been obtained in the fatigue for specimens with stress concentrators made of graphitic steel in the endurance range 10⁴–10⁵ cycles and a jumpwise effect has been established for the change in sensitivity factor q to stress concentration connected with these discontinuities and absence of them on fatigue curves for smooth specimens. The discontinuities on the fatigue curves obtained are explained using fractographic analysis of fatigue fractures on the basis of a hypothesis checked for the steels about a change in stressed state ahead of a developing crack from a plane stressed to a plane strained state.Siberian Metallurgical Institute, Novokuznetsk. Gorky Polytechnic Institute. Translated from Problemy Problemy Prochnosti, pp. 27–31, October, 1989.     

Microstructural study of Au-Pd-Zn ohmic contacts to p-type InGaAsP-InP

A detailed microstructural study has been done on Au-Pd-Zn ohmic contacts to p-type InGaAsP epitaxially grown on InP. The doping level in the InGaAsP was 1.0 × 10¹⁹ to 1.5 × 10¹⁹ cm^–3 near the surface with the Zn concentration graded to a value of 7 × 10¹⁸ cm^–3 at the InGaAsP-InP interface. Metal layers (10 nm Pd,3 nmZn, 25 nm Pd and 50 nm Au) were deposited sequentially by electron beam evaporation. Contact resistances less than 10^–4 cm² were achieved for all annealing temperatures studied (380–440 C) and a minimum contact resistance of 2 × 10^–6 cm² was obtained for an anneal at 400 C for 20 s. Comparisons were made to similar metallizations on p-type InP. Lower contact resistances were achieved for the quaternary material compared with the binary material, however, contact stability and uniformity were worse.     

SQUID behavior at liquid nitrogen temperature in high-T c superconductors of the type Y-Ba-Cu-O

Quantum interference at liquid nitrogen temperature in a bulk sample of high-T _c superconductor YBa₂Cu₃O_9–y is described. The SQUID quantization loop is formed at random inside the sintered sample as an internal percolation loop with a Josephson weak link. The estimated values of this multiply connected quantization loop are: the inductance of the loopL _SQ4×10^–10 H, the critical currentI _c1×10^–6 A, the area of the loopA1×10^–8 m², and the hysteresis parameter _L 1. In the flux-locked loop regime the field sensitivity of this liquid nitrogen SQUID with a random loop is 10^–9 T/Hz^1/2 and the resolution is 5×10^–3 ₀/Hz^1/2.     

Effect of surface condition on fatigue resistance of an AV alloy during program loading

Conclusions The tests performed over the loading spectrum considered are characterized by a change in the sum of the relative durabilities as a function of stress level from 0.33 to 0.65, during which the chief damage occurs over that portion of the spectrum above 0.75 _max.The scatter in the durabilities during program loading decreases with the increase in stress.The magnitude of the sum of the relative durabilities decreases with the increase in durability.Surface cold hardening increases the fatigue resistance under conditions of nonsteady-state loading. The coefficients attain values of 1.22–1.36 over the durability range 2·10⁶–2·10⁷ cycles.The spectrum studied is characterized by a concentration of defect intensity over the _max.A change in the level of the spectrum has insignificant effect on the intensity distribution of the defect accumulations.Moscow. Translated from Problemy Prochnosti, No. 4, pp. 18–22, April, 1970.     

Deviation from Wiedemann–Franz Law for the Thermal Conductivity of Liquid Tin and Lead at Elevated Temperature

The thermal conductivities of tin and lead in solid and liquid states have been determined using a nonstationary hot wire method. Measurements on tin and lead were carried out over temperature ranges of 293 to 1473 K and 293 to 1373 K, respectively. The thermal conductivity of solid tin is 63.9±1.3 Wm^–1K^–1 at 293 K and decreases with an increase in temperature, with a value of 56.6±0.9 Wm^–1K^–1 at 473 K. For solid lead, the thermal conductivity is 36.1±0.6 Wm^–1K^–1 at 293 K, decreases with an increase in temperature, and has a value of 29.1±1.1 Wm^–1K^–1 at 573 K. The temperature dependences for solid tin and lead are in good agreement with those estimated from the Wiedemann–Franz law using electrical conductivity values. The thermal conductivities of liquid tin displayed a value of 25.7±1.0 Wm^–1K^–1 at 573 K, and then increased, showing a maximum value of about 30.1 Wm^–1K^–1 at 673 K. Subsequently, the thermal conductivities gradually decreased with increasing temperature and the thermal conductivity was 10.1±1.0 Wm^–1K^–1 at 1473 K. In the case of liquid lead, the same tendency, as was the case of tin, was observed. The thermal conductivities of liquid lead displayed a value of 15.4±1.2 Wm^–1K^–1 at 673 K, with a maximum value of about 15.6 Wm^–1K^–1 at 773 K and a minimum value of about 11.4±0.6 Wm^–1K^–1 at 1373 K. The temperature dependence of thermal conductivity values in both liquids is discussed from the viewpoint of the Wiedemann–Franz law. The thermal conductivities for Group 14 elements at each temperature were compared.     

Thermal transport properties of helium near the superfluid transition. II. Dilute3He-4He mixtures in the superfluid phase

Measurements of the average thermal conductivity _exp hQ/T and of the thermal relaxation time to reach steady-state equilibrium conditions are reported in the superfluid phase for dilute mixtures of³He in⁴He. Hereh is the cell height,Q is the heat flux, andT is the temperature difference across the fluid layer. The measurements were made over the impurity range 2×10^–9<X(³He)<3×10^–2 and with heat fluxes 0.3<Q<160 µW/cm². Assuming the boundary resistanceR _b , measured forX<10^–5, to be independent ofX over the whole range ofX, a calculation is given for _exp. ForQ smaller than a well-defined critical heat fluxQ _c (X) X ^0.9, _exp is independent of Q and can be identified with the local conductivity _eff, which is found to be independent of the reduced temperature = (T–T)/T for –10^–2. Its extrapolated value at T is found to depart forX10^–3 from the prediction X ^–1 , tending instead to a weaker divergence X ^–a witha0.08. A finite conductivity asX tends to zero is not excluded by the data, however. ForQ >Q _c (X), a nonlinear regime is entered. ForX10^–6, the measurements with the available temperature resolution are limited to the nonlinear conditions, but can be extrapolated into the linear regime forX2×10^–7. The results for _exp(Q),Q _c (X), and _eff(XX) are found to be internally consistent, as shown by comparison with a theory by Behringer based on Khalatnikov's transport equations. Furthermore, the observed relaxation times (X) in the linear regime are found to be consistent forX>10^–5 with the hydrodynamic calculations using the measured _eff(X). ForX<10^–5, a faster relaxation mechanism than predicted seems to dominate. The transport properties in the nonlinear regimes are presented and unexplained observations are discussed.     

Bias voltage dependence properties of cadmium oxide films deposited by d.c. reactive magnetron sputtering

Cadmium oxide films were grown on glass substrates using d.c. reactive magnetron sputtering technique by sputtering from a metallic cadmium target in an oxygen partial pressure of 1×10^–3 mbar under various substrate bias voltages. The substrate bias voltage significantly influences the crystallographic structure of the deposited films. The influence of substrate bias voltage on the electrical and optical properties of the films was systematically studied. The films formed at a substrate temperature of 473 K and bias voltage of –80 V showed an electrical resistivity of 1×10^–3 cm, optical transmittance of 86%, optical band gap of 2.47 eV and a figure of merit of 7×10^{–3 –1}.     

Relaxation times and mass diffusion in superfluid dilute3He-4He mixtures

Relaxation times are reported from the transients observed during thermal conductivity _eff and thermal diffusionk _T ^* measurements in superfluid mixtures of³He in⁴He with a layer thickness of 1.81 mm. The experiments extend from 1.7 K toT and over a³He concentration range 10^–6X<5×10^–2. The agreement between the measured and the predicted from the two-fluid thermohydrodynamic equations is satisfactory forX>10^–3 but deteriorates for smaller³He concentrations. This situation is similar to that for _eff andk _T ^* results and indicates that the transport properties in very dilute mixtures with layers of finite thickness are not well understood. ForX>10^–3, the mass diffusion coefficientD _iso for isolated³He in⁴He has been determined from and from _eff measurements. There is an inconsistency by a constant numerical factor between these determinations. This problem might be related to the observations that in the superfluid phase, the relaxation times for different cell heightsh do not scale withh ². FromD _iso derived via the _eff data, the³He impurity-roton scattering cross section is determined. Comparisons with previous work are made.     

Nucleation control of diamond synthesized by microwave plasma CVD on cemented carbide substrate

Diamond was coated on to cemented carbide substrate by microwave plasma CVD, in which nucleation control of diamond crystals was investigated under constant deposition conditions; total pressure 30 torr, CH₄ flow rate 1 ml min^–1, H₂ flow rate 199 ml min^–1 and microwave power 550 W. Nucleation tends to occur selectively on the edge part of WC grains of the cemented carbide substrate with coarse WC grain size of about 1 m, where the nucleation density was 9×10⁶ cm^–2. The density increased to about 5×10⁷ cm^–2 when using a finegrained substrate (WC grain size 0.5 m). A considerably enhanced nucleation was observed by introducing a number of fine microflaws on to the substrate surface. Microflawing treatment with diamond fine powder (grain size 0–1/4 m) suspended in an ultrasonic cleaner bath was effective for increasing the diamond nucleation density up to 5×10⁸ cm^–2. The grain size of grown diamond crystals decreased with increasing microflawing time.     

Preparation of High-Purity Indium and Gallium via Electrotransfer in a Magnetic Field

High-purity (7N) indium and gallium are obtained via electrotransfer in melts placed in a static transverse magnetic field. The resistance ratios of the indium and gallium thus purified (25000 and 85000, respectively) are larger than in commercial grades of these metals. The magnetoresistance of liquid gallium is measured as a function of magnetic field. A multiband model for the Fermi surface of liquid gallium is proposed, which includes an electronic sphere of radius k _F ^e = 1.654 × 10⁸ cm^–1 and a spherical hole shell of thickness k = 0.5 × 10⁸ cm^–1 and radius k _F ^h = 1.114 × 10⁸ cm^–1. The model accounts for the observed magnetoresistive response of liquid gallium in a transverse magnetic field.     

Method of singular integral equations in linear and elastoplastic problems of fracture mechanics

A brief survey of investigations carried out at the Karpenko Physicomechanical Institute of the Ukrainian National Academy of Sciences and devoted to the application of the method of singular integral equations to the solution of two-dimensional problems of fracture mechanics is presented. Special attention is given to the integral equations defined on piecewise smooth closed or open contours appearing in the boundary-value problems of the theory of elasticity for angular domains. We propose a new method aimed at the solution of dynamic problems by using finite differences with respect to time and singular integral equations on the boundary contours. Integral equations also appear in the elastoplastic problems of fracture mechanics solved by using the model of plastic strips and in the general case of continual plastic zones.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 3, pp. 38–50, May–June, 2004.Lecture delivered at the Third International Conference Fracture Mechanics of Materials and Strength of Structures in Lviv on 22.06.2004.     

Electrical conductivity of iodine adducts of nylon 6 and other non-conjugated polymers

Iodine-nylon 6 adducts containing 70 to 90wt% iodine have been prepared by heating iodine and nylon 6 at 115 and 145° C. The electrical conductivity () of the adduct increases with increase in the iodine content and the iodine-nylon 6 adduct containing 90wt% iodine and prepared at 145° C gives = 10^–3 S cm^–1 at 25° C. Infrared, nuclear magnetic resonance (¹H and¹³C{1 H}), and powder X-ray diffraction analysis of the adduct show a profound change of the structure around the amide group of nylon 6 and suggest the formation of a-C=NH⁺-group in the reaction of nylon 6 with iodine. The temperature dependences of of the idoinenylon 6 adducts prepared at 115° C give activation energies of 51 to 92 kJ mol^–1 depending on the iodine content. Addition of carbon powder to the iodine-nylon 6 adduct causes an increase in electrical conductivity. Other polymers (aliphatic and aromatic nylons, poly(vinyl alcohol), poly (tetrahydrofuran), poly(N-vinylpyrrolidone), poly (4-vi nylpyridine), and poly(acrylonitrile)) which have lone pair or -electrons also form iodine adducts containing 70 to 95 wt % iodine and the adducts show an electrical conductivity in the range of 10^–5 to 10^–2 S cm^–1. Among the iodine adducts, those of poly(vinyl alcohol) and poly (tetra hydrofuran) show electrical conductivities as high as 1.5 X 10^–2 S cm^–1 when the adducts contain about 90 wt% iodine.     

Non-linear response of internal friction to tensile strain rate and frequency during plastic deformation of high-purity aluminium

The internal friction of high-purity aluminium during the process of plastic deformation was measured by a middle torsion pendulum on a modified tensile testing machine. The effects of tensile strain rate, , in the range of 0.73×10^–6 to 50×10^–6s^–1, and frequency of internal friction measurement, f, in the range of 0.38 to 2.6 Hz were studied. The results showed a non-linear dependence of internal friction, Q ^–1, on and f ^–1 or on (=2 f). The interrelationship between internal friction during the process of plastic deformation and dislocation motion, and the effect of non-linearity on the dynamic behaviour of dislocations are discussed.     

Containerless Property Measurements of Liquid Palladium

Some thermophysical properties of liquid and supercooled palladium were measured using containerless techniques. Over the 1640–1875 K temperature interval, the density could be expressed as (T)=10.66× 10³ –0.77(T–T_m)(kg·m^–3) and the ratio between the isobaric heat capacity and the hemispherical total emissivity could be rendered as (J·mol^–1·K^–1), where T_m=1828 K. The volume expansion coefficient was also determined as 7.2 × 10^–5 K^–1.     

Sulphonated poly(ether ether ketone): Synthesis and characterisation

The sulphonation of commercially available PEEK in powder form (Gatone, Gharda Chemicals Limited, India) was carried out using conc. H²SO⁴ under different reaction conditions. The duration of reaction was varied from 3–5 h, polymer concentration 4–10% (w/v) and temperature 35–50C. Structural characterisation of sulphonated polymers was done by elemental analysis, FT-IR and ¹H-NMR spectroscopy. The degree of sulphonation as calculated from ¹H-NMR and elemental analysis (S-content) was found to be in the range of 50–80%. Multistep mass loss was observed in thermogravimetric traces (recorded in N² atmosphere). The first step (50–225 ± 25C) was due to loss of moisture (1–10%) and second step (250–425 ± 25C) has been attributed to volatilization of SO³ from the sulphonic group. The backbone degradation takes place above 450C. The mechanical properties and proton conductivities of various sulphonated samples was also evaluated.     

Some characteristics of the CROG thermometer

Summary The results imply the following conclusions on the practical utilization of the thermometer, and on the characteristics of the thermometer: Temperatures measured by the CROG thermometer lie within the range from 3.7° to 3.1°K when the supply current ranges from 120 to 990 mA; no changes were observed in the sensitivity of the CROG thermometer over a year's time; the sensitivity of the CROG thermometer over the 3.7° to 3.1°K temperature range is respectively 6·10³ to 5·10² Hz · °K^–1; the error in measurements of the absolute values of the temperature on the T₅₈ scale may be small, and can attain values of 10^–4 to 10^–5 °K.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 30–31, September, 1972.