Simulation of ratcheting strain to a high number of cycles under biaxial loading

The Ohno–Wang kinematic hardening rule is modified to incorporate the Burlet–Cailletaud radial evanescence term for an improved simulation of the ratcheting behavior. The Delobelle parameter δ^′ is implemented in the modified model to compromise shakedown of the Burlet–Cailletaud hardening rule and over-prediction of the Ohno–Wang model. An evolution equation is proposed for δ^′ to simulate the ratcheting strain over an extended domain of cycles. Ratcheting tests were conducted on S45C steel under four types of nonproportional axial–torsional loading. The new model is found to yield reasonably accurate predictions of ratcheting strain to a much higher number of cycles compared with other studies.     

Problem of Increasing the Survivability of Two–Stage Ballistic Guns

The paper proposes methods for increasing the survivability of light–gas guns, including new designs and nonconventional modes of shot. It is established theoretically and experimentally that a decrease in the cone angle of the conical adapter to 2.5 — 3° leads to a severalfold increase in the survivability of the high–pressure chamber. A compound piston with a liquid or gel–like filler is designed. The mode of shot from a light–gas gun with superlight pistons and without a diaphragm is justified and tested experimentally. Conical and measuring adapters with liners made of thermally– and wear–resistant alloys are designed to prevent ablation of the light–gas gun barrel.     

Difference between low-volume and high-volume Andersen samplers in measuring atmospheric aerosols

The mass concentration and size distribution of aerosols in Tokaimura were investigated using a high-volume and a low-volume Andersen sampler. A difference was found using the two samplers： the concentration of total aerosols determined with the high-volume sampler is smaller than that of the low-volume sampler by 70-90% throughout the year. Compared to the high-volume sampler, low-volume sampler gave lower concentration for aerosols 〉7 μm, higher concentration for aerosols of 3.3-7.0 μm and 〈 1.1 μm, though similar results for aerosols of 1.1-3.3 μm. The low-volume sampler was found to have better separation efficiency and higher accuracy.     

Three-dimensional instability of an elliptic Kirchhoff vortex

The instability of a Kirchhoff vortex [1–3] with respect to three-dimensional perturbations is considered in the linear approximation. The method of successive approximations is applied in the form described in [4–6]. The eccentricity of the core is used as a small parameter. The analysis is restricted to the calculation of the first two approximations. It is shown that exponentially increasing perturbations of the same type as previously predicted and observed in rotating flows in vessels of elliptic cross section [4–9] appear even in the first approximation. As distinct from the case of plane perturbations [1-3], where there is a critical value of the core eccentricity separating the stable and unstable flow regimes, instability is predicted for arbitrarily small eccentricity.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 40–45, May–June, 1988.     

Influence of surface tension on damping of the oscillations of a viscous incompressible fluid in a cylindrical channel

A numerical calculation is made of small oscillations of a viscous incompressible fluid that fills half of a horizontal cylindrical channel. The calculation is made with and without allowance for surface tension. The results of the calculation show that allowance for surface tension increases the damping of the oscillations. The general properties of problems of the normal oscillations of a heavy and capillary viscous incompressible fluid were studied in [1–3], in which the possibility of applying the Bubnov-Galerkin method to these problems was pointed out. A method for calculating the oscillations of a viscous incompressible fluid that partly fills an arbitrary vessel at large Reynolds numbers was developed in [3–5].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 128–132, May–June, 1980.     

Fatigue and fretting fatigue of ion-nitrided 34CrNiMo6 steel

This work is concerned with the surface treatment (ion nitriding) of fretting fatigue and fatigue resistance of 34CrNiMo6. Tests are made on a servo-hydraulic machine under tension for both treated and non-treated specimens. The test parameters involve the applied displacements δ±80–±170 μm; fretting pressure σ_n=1000–1400 MPa; fatigue stress amplitude σ_a=380–680 MPa and stress ratio R=−1. The ion nitriding process improves both fatigue and fretting fatigue lives. Subsurface crack initiation from internal discontinuities was found for ion-nitrided specimens.     

Three-dimensional studies on bicomponent extrusion

The present work is concerned with the mathematical modelling and numerical simulation of three-dimensional (3-D) bicomponent extrusion. The objective is to provide an understanding of the flow phenomena involved and to investigate their impact on the free surface shape and interface configuration of the extruded article. A finite element algorithm for the 3-D numerical simulation of bicomponent stratified free surface flows is described. The presence of multiple free surfaces (layer interface and external free surfaces) requires special free surface update schemes. The pressure and viscous stress discontinuity due to viscosity mismatch at the interface between the two stratified components is handled with both a double node (u–v–w–P ₁ –P ₂ –h ₁ –h ₂) formulation and a penalty function (u–v–w–P–h ₁ –h ₂) formulation.The experimentally observed tendency of the less viscous layer to encapsulate the more viscous layer in stratified bicomponent flows of side-by-side configuration is established with the aid of a fully 3-D analysis in agreement with experimental evidence. The direction and degree of encapsulation depend directly on the viscosity ratio of the two melts. For shear thinning melts exhibiting a viscosity crossover point, it is demonstrated that interface curvature reversal may occur if the shearing level is such that the crossover point is exceeded. Extrudate bending and distortion of the bicomponent system because of the viscosity mismatch is shown. For flows in a sheath-core configuration it is shown that the viscosity ratio may have a severe effect on the swelling ratio of the bicomponent system.Modelling of the die section showed that the boundary condition imposed at the fluid/fluid/wall contact point is critical to the accuracy of the overall solution.     

Experimental study of heat and mass transfer from a horizontal cylinder in downward air-water mist flow with blockage effect

An experimental study was made on convective heat and mass transfer from a horizontal heated cylinder in a downward flow of air-water mist at a blockage ratio of 0.4. The measured local heat transfer coefficients agree fairly well with the authors' numerical solutions obtained previously for the front surface of a cylinder over the ranges mass flow ratio 0–4.5×10⁻², a temperature difference between the cylinder and air 10–43 K, gas Reynolds number (7.9–23)×10³, Rosin-Rammler size parameter 105–168 μm, and dispersion parameter 3.4–3.7. Heat transfer augmentation, two-pahse to single-phase of greater than 19 was attained at the forward stagnation point. For heat transfer in the rear part of the cylinder, an empirical formula is derived by taking into account the dimensionless governing variables, that is, coolant-feed and evaporation parameters.     

Connective instability of a two-layer system with thermally insulated boundaries

The investigation of the convective stability of mechanical equilibrium of two horizontal layers of immiscible fluids has revealed the characteristics of such systems [1–3]. In particular, it has been found that, as distinct from a homogeneous horizontal layer, under certain conditions two-layer systems experience convective instability when uniformly heated from above and, moreover, oscillatory instability when heated from below. In [1–3] the problem was solved for a system with isothermal outer boundaries. In this paper the stability of equilibrium of two-layer systems is investigated for thermally insulated outer boundaries. Special attention is given to the study of the long wave instability mode.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 22–28, March–April, 1986.The authors wish to thank O. V. Kustova for assisting with the computations.     

Equilibrium and stability of three capillary fluids with a common line of contact

Systens with a line of contact of three capillary fluids, which are fairly widely distributed in nature, began to be studied only in comparatively recent times [1–3]. The conditions for equilibrium and stability of such systems in a vessel are formulated in what follovs on the basis of variational principles.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 170–173, May–June, 1986.The author is grateful to A. D. Tyuptsov for discussing the study with him.     

Micromechanical study of formation and evolution of martensite for Cu–Al–Ni single crystal by moiré interferometry

The basic properties of pseudoelasticity of Cu–Al–Ni single crystal are studied to analyze the morphology associated with the formation and evolution of martensite and the shape memory recovery process at different temperatures. Use is made of a multifunctional macro–micro moiré interferometry measurement system. The β₁ to β₁^′ phase changes are identified with the stress-induced transformation of a Cu–13.7%Al–4.18%Ni (wt%) alloy. The invariant plane between the martensite and the parent phase is shown directly by fringe patterns. It is found that martensite appears in the shape of bands or thin plates on the surface of the specimen. The formation of martensite is a very rapid process and martensite ‘jumps' out until the specimen is completely transformed into a single variant. The results reveal the mechanism and process of stress-type and temperature-induced martensitic transformation.     

Stable nonlinear waves in a poiseuille flow

Nonlinear Tolmin-Schlichting waves are studied [1–8]. The investigation is carried out by means of a modified Stuart-Watson method [1–3]. In the case of a rigid regime of excitation terms to the fifth order are taken into account in expansions with respect to the amplitude of self-excited oscillations. The stability of self-excited oscillations with respect to two- and three-dimensional disturbances is examined.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 40–45, September–October, 1978.The author thanks S. Ya. Gertsenshtein for attention to the work and discussion of the results.     

Comparisons of different procedures of pre-compaction stress determination on weakly structured soils

Compaction is an important component of soil degradation. In this regard, the pre-compaction stress (σ_pc) concept is considered useful in mechanized agriculture nowadays. When the external forces exceed the internal strength (σ_pc) of soil, soil structure and soil physical quality will deteriorate. This concept was introduced at first for confined consolidation of non-structured, homogenized and saturated subsoils in civil engineering, though it is also suitable for agricultural conditions where the topsoil and subsoil are considered and both are often structured, heterogeneous and unsaturated. The best method for predicting σ_pc is by the plate sinkage test (PST) in the field, but it is expensive and time-consuming. This study was conducted to find an alternative laboratory method besides the confined compaction test (CCT) for predicting σ_pc. The CCT may not be a good method, especially at higher water contents, and for soils with low organic matter content, because of low sharpness of the critical region on the stress–strain curves. The study was performed on five soil types with a range of soil textures and organic matter content from central Iran using three loading types and three pF (i.e. Log [soil matric suction in cm]) values of 2.3, 2.7 and 2.9 with two replicates. Loading types consisted of CCT, the semi-confined compaction test (SCCT) and the kneading compaction test (KCT) at three maximum (or pre-compaction) stresses of 200, 400 and 600 kPa. The experiment was a completely randomized factorial design. The aim was to determine how accurately each loading type test could predict σ_pc of soil pre-compacted by one of the other methods. The applied combinations of CCT–SCCT, SCCT–CCT and KCT–CCT mean that the soil was pre-compacted by the first loading type and evaluated by the second one. The results showed that σ_pc and the sharpness of the σ_pc region were significantly affected by loading types as well as the soil conditions. The sharpest σ_pc region was observed in SCCT and the least sharp in CCT with the overall order being CCT–SCCT > SCCT–CCT > KCT–CCT. The sharpness of the σ_pc region was reduced for the soil samples with higher water content and coarser texture. Regardless of the soil and loading conditions, the prediction by SCCT was consistently more accurate than by CCT. The prediction of σ_pc by SCCT was more precise in comparison with CCT especially at higher stresses and soil water contents. However, the prediction of σ_pc by SCCT was very accurate at pF values of 2.7 and 2.9, and with low σ_pc values, when compared with the actual values of the σ_pc. For the clay soil at a pF value of 2.3, no pre-compaction region (i.e. zero σ_pc) could be determined by CCT at a maximum axial stress of 600 kPa. This was because of the incompressibility of soil water at this near-saturated soil condition at high stress. However, the sharpness of the critical region in SCCT was high enough to predict σ_pc satisfactorily. There was no significant difference between the combinations of SCCT–CCT and KCT–CCT in predicting σ_pc. The SCCT is a compromise method that lies between CCT and PST. SCCT has the advantage of using a limited and definite soil volume that can be modeled as a soil element. Marginal effects of disturbance caused by coring/sampling as well as pre-test sample preparation seem to have minor effects on the stress–strain curve determined by SCCT in comparison with CCT. Moreover, the soil volume needed for this test is the same as for CCT.     

The nonlinear evolution of two-dimensional and three-dimensional waves in mixing layers

The authors consider problems connected with stability [1–3] and the nonlinear development of perturbations in a plane mixing layer [4–7]. Attention is principally given to the problem of the nonlinear interaction of two-dimensional and three-dimensional perturbations [6, 7], and also to developing the corresponding method of numerical analysis based on the application to problems in the theory of hydrodynamic stability of the Bubnov—Galerkin method [8–14].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhldkosti i Gaza, No. 1, pp. 10–18, January–February, 1985.     

On nonisothermal electroconvection

The flow from the tip of a needle electrode is caused by the Coulomb force acting on the space charge [1–3]. This charge is formed because of the dependence of the conductivity on the temperature, nonuniformity of which is due to Joule heating [1] and the electric field intensity [2] or processes near the electrode [3–5]. The present paper considers the stability of a dielectric liquid between spherical electrodes in order to elucidate the possibility of a thermoelectrohydrodynainic flow due to Joule heating. In the presence of external heating, the possibility of such a flow has been demonstrated both experimentally and theoretically [6–8].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 133–137, March–April, 1980.     

Effect of streamline curvature on flow field of a turbulent plane jet in cross-flow

The effects of the streamline curvature and finite edge velocity on the flow field of a turbulent plane jet in cross-flow are studied numerically by incorporating the curvature effect in the k–ε turbulence model. The improvement in the predictions by the streamline curvature model is assessed by comparing its prediction with those by the standard k–ε model. The predictions by both the models are compared with available experimental data. It has been observed that the performance of the k–ε model with streamline curvature modification is superior to the standard k–ε model.     

Thin axisymmetric cavities in a subsonic compressible flow

The investigation of subsonic compressible flow past thin axisymmetric cavities carried out in [1–3] is continued by the method of asymptotic expansions. The dependence of the elongation of the cavity on the cavitation number and the Mach number is obtained.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 174–177, September–October, 1987.The author is grateful to Yu. L. Yakimov for discussing his results.     

Conditional moment closure and large-scale fluctuations of scalar dissipation

The accuracy of the method of calculating turbulent reacting flows [1–3] which is based on the use of the conditional mean concentrations of the reacting components is analyzed. The effect of large-scale fluctuations of the dissipation of passive admixture concentration [4–6] on the accuracy of the equations for the conditional means is considered and the corresponding corrections are computed. By means of numerical calculations the models for the conditional moment and traditional calculation methods are compared, as are the various approaches to the computation of the coefficients of the equations for the conditional means.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 50–59, September–October, 1993.The author wishes to express his wann thanks to A. B. Vatazhin for discussing the work and making useful comments.     

Dynamic problem for a two-layer medium with a vibrational source at the boundary interface

The present study is concerned with an analysis of gravitational and acoustic waves which are excited by a vibrational source deeply placed in a liquid covered by ice. An analysis of the rigidity characteristics of ice modeled by an elastic layer or by a Kirchhoff plate is done by factorization of the solution to the integral equation equivalent to an initially combined boundary value problem. The uncombined boundary condition is used to solve problems for unrestricted ice fields in [1–3], whereas combined conditions with vibrational sources positioned at the boundary of the medium are used in [4].Translated from Zhurnal Prikladnoi Mekhaniki, No. 3, pp. 125–129, May–June, 1986.     

A rheological investigation of solid soap

Summary The rheological behaviour of solid soaps has been investigated over several orders in time and shear by means of creep experiments, measurement of stressstrain curves at constant shear rate and dynamic experiments. The modulus at small deformations is almost constant over a frequency range of 10^–3–10³ Hz; a transition from linear to non-linear behaviour has been observed at a strain of about 10^–3. The results suggest that some kind of network structure is responsible for the rheological behaviour of soap.

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Zusammenfassung Das Theologische Verhalten von Hartseifen wurde für mehrere Größenordnungen von Zeit und Schubgeschwindigkeit untersucht mittels Kriechversuche, Messung der Spannungs-Deformationskurven bei konstanter Schubgeschwindigkeit und dynamischer Experimente. Der Modul bei geringen Deformationen ist fast konstant im Frequenzbereich von 10^–3–10³ Hz; ein Übergang von linear zu nicht-linear wurde bei einer Deformation von etwa 10^–3 beobachtet. Die Ergebnisse lassen auf eine netzartige Struktur schließen, die für das Theologische Verhalten der Seife verantwortlich ist.

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The authors are indebted to Mr.C. J. Nederveen of the Central Laboratory T. N. O., Delft for the dynamic measurements, and thank Mr.D. W. Brinkman of the Unilever Research Laboratory, Vlaardingen for experimental assistance.