Thermomicrohardness analysis (TμHA) of glassy materials

A thermal analysis technique and an apparatus are described which are used to study phase transformations in glassy materials by monitoring the temperature dependence of the microhardness through a phase transformation with the heating rate varied as a parameter. The method has been named Thermomicrohardness Analysis (TμHA). The glass transformation behaviors of a-As₂Se₃ xerographic photoreceptor type films have been studied to elucidate the nature of structural changes in the glass transformation region of glasses. It is shown that on an Itoh-Shishokin plot the Vickers microhardness exhibits a sharp fall in the glass transition interval due to a relaxation phenomenon similar to the relaxation of the enthalpy as determined by DSC measurements. Furthermore it is shown that the relaxation rate in both the processes is inversely proportional to the instantaneous viscosity.     

Investigation of supersonic viscous flow past a sphere in the presence of subsonic and sonic injection

Supersonic flow past a sphere with a given rate of gas injection along the generator is investigated numerically on the range Re=10²–10⁴. Calculations have been made on the interval 0 90°, where is the angle between the axis of symmetry and the normal to the surface. It is shown that for high subsonic and sonic injection rates it is possible to observe qualitatively new features in the flow structure and in the distribution of the local supersonic flow characteristics around the perimeter of the sphere not previously noted in [9]. In the case of sonic injection the changes in flow structure occur only in the supersonic zone. In the neighborhood of the transition from a subsonic to sonic injection velocity the heat flux has a local maximum, which in absolute value does not exceed the heat flux in the absence of injection. It is shown that there may be qualitative differences in the pressure distribution over the surface of the body with increase in the injection parameter depending on the distribution and value of the injected gas flow rate and, moreover, the number Re.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 83–89, January–February, 1988.     

End Effects for Anti-Plane Shear Deformations of Periodically Laminated STrips with Imperfect Bonding

The axial decay of Saint-Venant end effects is investigated for anti-plane shear deformations of semi-infinite generally laminated anisotropic strips. Imperfect bonding conditions are imposed at the interfaces. The analytical approach, using a displacement field which decays exponentially in the axial direction, gives rise to a transcendental equation for the real eigenvalues. The decay rate for the stresses is given in terms of the smallest positive eigenvalue. Laminated strips with periodic layout are then considered. In the presence of imperfect bonding, the effective shear elastic moduli, computed through a homogenization method, depend on the total number of slipping interfaces in the laminate. Numerical examples confirm that the decay lengths computed with effective shear moduli represent the asymptotic values (for an increasing number of layers) for those of periodically laminated strips. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nonlinear steady-state oscillations of an elastic plate floating on the surface of a liquid of finite depth

In addition to obtaining solutions by the perturbation method it is shown that in the case of nonlinear wave interaction given a certain relationship between the parameters of the interacting waves steady-state compound waves may exist.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 146–154, May–June, 1989.     

Source below the free surface of a heavy liquid

The problem of the motion of a source under the free surface of an infinitely deep heavy liquid has been studied by Keldysh [1] under the assumptions used in the theory of small amplitude waves. However, these assumptions are no longer valid [2] for large Froude numbers F.A method using only one of the four assumptions of small amplitude wave theory (the assumption that the absolute value of the velocity at the free surface is nearly constant) was described in [2], In the following, this method is used to construct a solution of the problem which becomes exact as F . When F is not large our results are close to those of Keldysh if the source intensity is low. For F=0, both methods lead to exact results.     

Creep in materials with different tension and compression behavior

Experimental data on creep in tubular specimens loaded in tension and in compression are cited. It is demonstrated experimentally that the resulting vector of the creep strain rates is orthogonal to the curve of constant scattering intensity. Approximate analytical formulas making it possible to describe the creep process undergone by materials having different behavior patterns in tensile and compressive loading are derived.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 136–139, September–October, 1970.     

Electrohydrodynamic monodispersion of liquids

In electrostatic dispersion of a liquid from a meniscus at the end of a capillary through which the liquid is passed the emitted droplets are unstable with respect to their self-charge and break up, ejecting about 100 smaller (by two orders of magnitude) droplets. However, if the liquid is passed through the capillary under pressure, then, depending on the pressure, there exist ranges of values of voltages applied to the electrodes for which the emitted droplets are stable both with respect to their self-charge and with respect to the external electric field of the system of electrodes. In this paper, the sizes, charges, and specific charges of such droplets are calculated on the basis of the principle of least dissipation of the energy.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 32–40, March–April, 1991.     

Subcritical Motions of a Fluid with Temperature-Dependent Viscosity

Convective motions of a fluid with temperature-dependent viscosity are studied using numerical experiments. The results obtained provide data for laboratory experiments aimed at determining the hardness of the instability.     

Fluid dynamics of self-propelled microorganisms,from individuals to concentrated populations

Nearly close-packed populations of the swimming bacterium Bacillus subtilis form a collective phase, the “Zooming BioNematic” (ZBN). This state exhibits large-scale orientational coherence, analogous to the molecular alignment of nematic liquid crystals, coupled with remarkable spatial and temporal correlations of velocity and vorticity, as measured by both novel and standard applications of particle imaging velocimetry. The appearance of turbulent dynamics in a system which is nominally in the regime of Stokes flow can be understood by accounting for the local energy input by the swimmers, with a new dimensionless ratio analogous to the Reynolds number. The interaction between organisms and boundaries, and with one another, is modeled by application of the methods of regularized Stokeslets.     

Application of material forces to fracture of inhomogeneous materials: illustrative examples

The material forces concept has become an elegant tool in continuum mechanics for the calculation of the thermodynamic driving force of a defect. Based on this concept, we have recently shown that inhomogeneities essentially shield or anti-shield crack tips from applied far-field stresses. The goal of this paper is to illustrate this by considering the model example of a crack in a CT-type specimen that contains a bimaterial interface. The crack driving force is calculated as the sum of the far-field driving force and the crack-tip shielding or anti-shielding. Several cases of inhomogeneity in either thermal or elastic properties are considered. Rather simple hand calculations are provided in addition to numerical results to illustrate the advantages of using the material forces concept.