Shear induced phase transitions in highly dilute aqueous detergent solutions

Aqueous solutions of some cationic detergents show rheopectic behaviour at very low concentrations. Rheological measurements and the electrical anisotropy of the streaming solutions indicate that the rheopectic behaviour of the solutions is due to a shear induced phase transition.     

Plastic flow and dislocation structure at small strains in OFHC copper deformed in tension,torsion and combined tension-torsion

OFHC copper specimens of 39 μm grain size were deformed to small strains (up to 8%) in tension, torsion and combined tension-torsion at 300 K and the resulting dislocation structures, distributions and densities were determined using transmission electron microscopy. Employing the von Mises yield criterion and the plastic-work hypothesis good agreement was obtained for the three testing conditions for (i) equivalent stress $\text{}\text{?}$gs vs equivalent strain $\text{}\text{?}$g3^p curves, (ii) the dislocation structure, distribution and density ρ as a function of $\text{}\text{?}$g3^p, and (iii) $\text{}\text{?}$gs as a function of $\text{ρ}\text{1}\text{2}$. Furthermore, upon comparing the $\text{}\text{?}$gs vs $\text{ρ}\text{1}\text{2}$ curve for polycrystalline copper with the τ_RSS vs $\text{ρ}\text{1}\text{2}$ curve for single crystals, an average Taylor factor M= (σ/τ_RSS) of approximately 3.2 was obtained, which is in good accord with that predicted theoretically for FCC metals. Almost equally good correlations for the stressstrain curves and for the dislocation density were obtained on the basis of maximum shear stress τ_max and maximum shear strain γ^p_max as on the basis of $\text{}\text{?}$gs and $\text{}\text{?}$g3^P. Therefore, the present results do not permit a positive decision on the question whether the dislocation density correlates better with $\text{}\text{?}$gs and $\text{}\text{?}$g3^P or with τ_max and γ^P_max.A single test in which the direction of straining in torsion was reversed yielded a density and distribution of dislocations (and a corresponding value of $\text{}\text{?}$gs) equivalent to those that developed at a smaller strain in unidirectional straining.     

Boundary layer development in an MHD duct

This study presents a method of calculation for two-dimensional, steady-state, laminar flow in the entrance region of an MHD duct. The electrically conducting fluid in the free stream is compressible whereas the medium in the boundary layer itself is taken to be incompressible. Thus, the density is variable in the axial direction of the duct only, and the momentum and energy equations for the boundary layer are uncoupled. These equations are solved using an extended Von Kármán-Pohlhausen method as described by U. P. Hwang for a compressible MHD flow with zero electric field. In this study, however, the electric field is essentially not zero and the MHD duct can work as a generator. The equations of the insulator boundary layer are solved in the assumption that the displacement thickness of the electrode boundary layer equals that of the insulator boundary layer, so the total influence of the varying effective crossection on the free stream is taken into account. In this way a quick method of calculating the MHD flow in the entrance region of a duct is obtained.     

Stress and deformation analysis from reduced-scale plastic-model testing

The use of scale models, which are made from plastic material, for stress and deformation analysis of missile nose-cone structures is discussed. The special strain-gage application and testing techniques, which are required because of the use of plastic materials, are detailed.The utilization of relatively inexpensive simplified models for the investigation of two specific design conditions is cited. The first case is a stress and deformation study of a thin, constant-thickness, shallow spherical shell which is supported by a circumferential line reaction and subjected to uniform external pressure. Comparisons are made with a recently published theoretical analysis of the problem.The second case is a particular design problem which is concerned with the determination of the stress and deformation in a variable-thickness, shallow spherical shell with several various-size cutouts. The shell is loaded with a varying external-pressure load which is reacted by a circumferential line load at the periphery. Influence curves for both stress and deformation are given.Some limitations of plastic-model testing are reviewed, and guides to successful use of the method are given.Paper was presented at 1959 SESA Spring Meeting held in Washington, D. C. on May 20–22.     

Temperature development based on technological analysis: Fast rolling as an example

Summary The mean rise in temperature with plastic strain due to the work of plastic deformation, taking account of the temperature-dependence of yield stress, is investigated when conduction effects are neglected and results for one particular example are presented. An adaptation of the well-known Siebel-Karman analysis for sheet rolling is examined, and results for the particular case of rolling a medium carbon steel are given in detail. The temperature-dependent property of the yield stress in cold-rolling at moderate reductions is shown not to have a large effect on factors such as roll-torque, though the actual temperature increase generated is a significant one. Examples are given of how the temperature of the material increases in its passage through the roll gap.     

On vortex shedding behind a circular disk

Abtract  Experiments were performed for individual realizations of the vortex shedding process behind a circular disk at Reynolds numbers of 10³–10⁵, at which periodic vortex shedding prevails in the wake. The phase differences regarding the individual vortex shedding structures detected at multiple circumferential locations in the wake were obtained by analyzing the hot-wire signals with a conditional-sampling scheme. The phase differences of vortex shedding detected at circumferential positions 90° apart show a wide scatter, but the anti-phase character is largely preserved in the individual vortex shedding process as detected at circumferential locations 180° apart. The randomness of phase differences involved in the vortex shedding process is noted to be essential in order to satisfy the axisymmetric property of the global flow. Received: 4 April 19969/Accepted: 29 January 1997     

Optimal Control of a Tethered Subsatellite of Three Degrees of Freedom

The paper presents the optimal control of the deployment and retrieval processes of a tethered subsatellite system of three degrees of freedom, which takes not only the in-plane motion, but also the out-of-plane motions, into account. After the statement of the optimal control problem of the tethered subsatellite system based on the dynamic equation of the system, with the control cost and the state constraints included, the paper introduces the quasilinearization and the truncated Chebyshev series to approximate the state variables of the system such that the original problem of constrained nonlinear optimal control is simplified into a set of linear quadratic programming problems which can be easily solved. The case studies in the paper not only support the new method, but also show that the controlled trajectories of the deployment process and the retrieval process are geometrically symmetric to each other with respect to the local vertical axis, and that the subsatellite always undergoes a slow, damped oscillation when it is in the beginning of a deployment process or at the end of a retrieval process.     

Blast wave measurements close to explosive charges

The paper reports the results of experimental measurements of the reflection pressures close to spherical charges of TNT. These measurements were made using a pressure bar technique. Charge weights of up to 3.6 kg were used, with the reflecting plane in the range 25 to 300 mm from the charge surface.A possible wave interaction model is discussed, to account for the observed pressure profiles, and its qualitative correctness checked by means of numerical simulation.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Ein interaktives Verfahren zur Auswertung von Kaustiken an Trennflächenrissen

Übersicht In diesem Beitrag wird eine auf der interaktiven numerisch/graphischen Bildverarbeitung beruhende Methode zur Ermittlung der Spannungsintensitätsfaktoren, für Trennflächenrisse in Verbundmaterialien vorgestellt. Eine Anzahl von detenpunkten entlang der experimentell aufgezeichneten Kaustik wird als Eingabe verwendet. Das Verfahren überprüft die Genauigkeit und Zuverlässigkeit der Ergebnisse selbst, indem die auf der Basis des Resultats numerisch generierte Kaustik mit der experimentellen verglichen wird.

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An interactive method for data processing from crack tip caustics at interfaces

Summary An interactive numerical-graphical image processing method for the evaluation of stress intensity factors at interface cracks in composites will be presented. Based on a set of experimental data points suitably chosen along the caustic the multipoint overdeterministic data reduction technique provides reliable and rapidly coverging results by cross-checking experimental caustics with numerically generated iterative caustics.

     

Analytical investigation of Bénard-Marangoni convection heat transfer in a shallow cavity filled with two immiscible fluids

The mechanism of natural and Marangoni convection in a system with two stratified fluid layers without mass transfer at the interface is investigated. The basis of the analytical solution is an assumption of parallel flow over a large portion of the system. The two cases of heat fluxes through horizontal or vertical opposite walls are considered. It is demonstrated that four different patterns of convection can be observed in the present system. The zone of occurrence of these flow patterns are specified in terms of non-dimensional parameters. Velocity and temperature distributions, stream function and Nusselt number are presented over a wide range of the governing parameters. The results obtained are explained in terms of the basic physical mechanisms that govern these flows showing many interesting aspects of the complex interaction between the buoyant and surface tension mechanisms.