An improved model for the analysis of deformation and stability of multilayer viscoelastic shells

We propose a numerical procedure for the analysis of stability of viscoelastic multilayer shells of revolution based on an improved two-dimensional model. The calculations are performed under the assumption that the layers of the shell are made of orthotropic composite materials and their creep can be described within the framework of linear hereditary theory. We study the problem of stability of a five-layer conic shell with elastic load-carrying layers and viscoelastic fillers loaded by uniform external pressure. Translated from Problemy Prochnosti, No. 5, pp. 89–94, September–October, 1997.     

Approximate method for the analysis of stability of beams under the action of a system of longitudinal and transverse forces

We propose an approximate method for the analysis of stability of uniplanar bending of beams under the action of a complex system of longitudinal and transverse forces, obtain formulas for the determination of the critical values of total longitudinal and transverse forces and the factor of stability of flange and rectangular beams that are convenient for practical applications, and present examples of the numerical analysis of actual beams. The critical values of the total forces obtained by the proposed method are compared with known results. The difference between the exact and approximate critical values does not exceed 2–7%. The experimental data enable us to recommend these approximate formulas for practical calculations of the stability of uniplanar bending of beams subjected to the combined action of complex systems of longitudinal and transverse forces. Translated from Problemy Prochnosti, No. 3, pp. 69–77, May–June, 1998.     

The Long-Term Drift of Triple-Point-of-Water Cells

As the triple point of water is of great importance for the International Temperature Scale of 1990 (ITS-90) and for the definition of the unit of thermodynamic temperature, its long-term stability has attracted a great deal of attention. In a study of long-term stability, a mystery has been uncovered. Some triple-point-of-water cells remain stable for many decades, while others decrease with increasing age of the cells, which is called long-term drift. To investigate this mystery, we used cells with different manufacture dates ranging from 1974 to 2002 and compared their analyses, which were done in 1984 and 2003. Using the same model of long-term drift as that used by Hill, the long-term drift rates of the two data sets are –4.7 μK·year⁻¹ and –9.2 μK·year⁻¹, respectively. One is consistent with the observed depression of about –4 μK·year⁻¹ measured by Hill, whereas the other differs greatly from Hill’s result. In addition, corresponding factors influencing long-term drift are discussed in this paper.     

Effects of Mesh Motion on the Stability and Convergence of ALE Based Formulations for Moving Boundary Flows

This paper investigates the effects of mesh motion on the stability of fluid-flow equations when written in an Arbitrary Lagrangian–Eulerian frame for solving moving boundary flow problems. Employing the advection-diffusion equation as a model problem we present a mathematical proof of the destabilizing effects induced by an arbitrary mesh motion on the stability and convergence of an otherwise stable scheme. We show that the satisfaction of the so-called geometric conservation laws is essential to the development of an identity that plays a crucial role in establishing stability. We explicitly show that the advection dominated case is susceptible to growth in error because of the motion of the computational grid. To retain the bound on the growth in error, the mesh motion techniques need to account for a domain based constraint that minimizes the relative mesh velocity. Analysis presented in this work can also be extended to the Navier–Stokes equations when written in an ALE frame for FSI problems.     

Long-wavelength stability of an unsupported multilayer liquid film falling under gravity

The long-wavelength stability of an unsupported multilayer liquid film falling under the effects of gravity and surface tension is investigated. By considering the Navier–Stokes equations for two fluid layers in the high-Reynolds-number and small-aspect-ratio limits the steady-state solutions are obtained. The stability criterion found by Lin (J Fluid Mech 104:111–118, 1981) for a one-layer fluid curtain is generalised to the two-layer case and the criterion for an n-layer curtain is established.     

High temperature phase stabilized microstructure in Mg–Zn–Sn alloys with Y and Sb additions

Mg–Zn–Sn alloys exhibit poor structural stability at elevated temperatures that restricts utilization of these alloys. Small additions of alloying elements forming high temperature phases (HTP) were used to improve the structural stability of the Mg–Zn–Sn alloy. The main goal of this work was to investigate the microstructure evolution of the Mg–Zn–Sn-alloy with additions of Y and Sb during a wide scope of heat treatments, and to elucidate peculiarities of an HTP-stabilized microstructure. In order to clarify the substructure features and phase precipitation after each step of the heat treatment, XRD, TEM, SEM and EDS analyses were applied. It was found that in the dendrite structure formed during solidification, HTP-particles are concentrated in the inter-dendrite regions. Solution treatment of the as-cast structure at 440 °C for 96 h lead to the formation of α-Mg grains of 50–80 μm in diameter with a characteristic substructure. The presence of HTP-particles prevented dislocation recovery and movement of dislocation walls during solution treatment, and by this way restricted annihilation of grain boundaries between dendrites of close orientation, and lead to the formation of a substructure with sub-grains of 20–30 μm. The sub-grain boundaries are pinned by HTP-particles and are strengthened by the MgZn₂ and Mg₂Sn binary precipitates during aging. Precipitate depleted zones formed near grain- and sub-grain boundaries during aging were bordered by a “crust” of enlarged binary particles. Such pinned sub-grain microstructure provides a high structural stability of the alloys at elevated temperatures.     

Organic solvent treatment and physicochemical properties of nanoporous polymer–SBA-15 composite materials

Mesoporous polymer–silica composites are attractive new materials because these systems can combine the advantages of highly porous silica and the vast functional diversity of organic polymers in a single robust structure. This contribution deals with the effects of organic solvent treatment on the physicochemical properties of mesostructured polymer–SBA-15 silica nanocomposites. For this study, two distinct reference mesoporous nanocomposites were prepared using a previously reported surface-confined polymerization technique, e.g., poly(styrene)(PS)–SBA-15 composite and poly(2-hydroxyethyl methacrylate)(PHEMA)–SBA-15 composite. The resulting materials are treated either with chloroform or toluene under heating for a prolonged period of time (24 h). Both materials are characterized prior and after solvent treatment by nitrogen physisorption at −196 °C, thermogravimetry and Attenuated Total Reflection Infra-Red (ATR-IR) spectroscopy. In general, solvent stability is excellent for both types of composite, even for low cross-linking degree of the polymer. Our data reveal that a treatment of mesoporous PHEMA–SBA-15 with chloroform or toluene has a minor, but reproducible, effect on the composite material in terms of porosity. Here, a reorganization of the polymer layer–silica interface seems to occur to some extent, which is leading to slight variation of the intrawall porosity. As a consequence, an increase of the thermal stability is clearly observed, with, however, no marked difference in the mean mesopore diameter. On the other hand, the PS–SBA-15 composite treated with the same solvents shows higher specific surface area values and an improved homogeneity in terms of polymer coating compared to untreated materials, especially for composites synthesized using benzoyle peroxide as the polymerization initiator. However, no increase in thermal stability is observed in this case.     

Effect of adding Ce on interfacial reactions between Sn–Ag solder and Cu

We investigated the effect of adding cerium (Ce) to low Ag content Sn–1.0wt.%Ag solder on the interfacial reactions between the Sn–1.0Ag solder and Cu substrate. The formation and growth of interfacial intermetallic compounds (IMCs) between the Sn–1.0Ag–0.3Ce solder and Cu substrate were studied and the results were compared to those obtained for the Ce-free Sn–1.0Ag/Cu and most promising Sn–3.0Ag–0.5Cu/Cu systems. The addition of Ce to the Sn–Ag solder significantly reduced the growth of the interfacial Cu–Sn IMCs, retarded the interfacial reactions between the solder and the substrate, and prevented the IMC from spalling from the interface. The Sn–1.0Ag–0.3Ce solder alloy had a good interfacial stability with the Cu substrate during solid-state isothermal aging in the viewpoint of IMC growth.     

Multiscale space–time fluid–structure interaction techniques

We present the multiscale space–time techniques we have developed for fluid–structure interaction (FSI) computations. Some of these techniques are multiscale in the way the time integration is performed (i.e. temporally multiscale), some are multiscale in the way the spatial discretization is done (i.e. spatially multiscale), and some are in the context of the sequentially-coupled FSI (SCFSI) techniques developed by the Team for Advanced Flow Simulation and Modeling (T \bigstar AFSM){({\rm T} \bigstar {\rm AFSM})}. In the multiscale SCFSI technique, the FSI computational effort is reduced at the stage we do not need it and the accuracy of the fluid mechanics (or structural mechanics) computation is increased at the stage we need accurate, detailed flow (or structure) computation. As ways of increasing the computational accuracy when or where needed, and beyond just increasing the mesh refinement or decreasing the time-step size, we propose switching to more accurate versions of the Deforming-Spatial-Domain/Stabilized Space–Time (DSD/SST) formulation, using more polynomial power for the basis functions of the spatial discretization or time integration, and using an advanced turbulence model. Specifically, for more polynomial power in time integration, we propose to use NURBS, and as an advanced turbulence model to be used with the DSD/SST formulation, we introduce a space–time version of the residual-based variational multiscale method. We present a number of test computations showing the performance of the multiscale space–time techniques we are proposing. We also present a stability and accuracy analysis for the higher-accuracy versions of the DSD/SST formulation.     

Numerical study of the stability of solutions for the half-space Ginzburg–Landau model

Based on a shooting alternative that allows one to numerically solve the one-dimensional system of Ginzburg–Landau in an unbounded domain, a numerical study of the stability of solutions of this system is performed here. This stability notion, from a physical point of view, means that each solution of the system is identified as stable when it minimizes the corresponding Ginzburg–Landau functional. As opposed to a previous paper, the present one is concerned with a more general study since the weak and large regimes of the Ginzburg–Landau parameter are considered and the initial data are no longer subject to the de Gennes condition. Certain conjectures regarding the superheating field are also investigated numerically.     

Stability of imperfect cylindrical shells

A procedure of approximate evaluation of the critical loads of shells proposed earlier on the basis of the nonlinear theory of shells is used to analyze the influence of initial imperfections of any shape on the parameters of the critical loads. The numerical results are compared with the available experimental and theoretical data corresponding to the complete loss of stability of shells and exhaustion of their load-carrying capacity. __________ Translated from Problemy Prochnosti, No. 4, pp. 94–101, July–August, 2008.     

Imogolite as an electron emitter and a water sensor

We investigated field emission (FE) properties of imogolite including the turn-on field and lifetime stability. Imogolite is an excellent electron emitter with a turn-on field of approximately 2.5–3.5 V/μm. A lifetime test revealed that imogolite protects itself during FE under exposure to O₂ gas. We also measured the current–voltage characteristics of the imogolite as a function of the amount of water adsorbed on the surface. The results suggested that the electrode-containing imogolite device could be a useful water sensor in a nanoscale environment.     

Mixed-hybrid scheme of the finite element method for solving the problems on bending,free vibration,and stability of plates

To solve a problem on bending, vibration, and stability of plates, a hybrid finite element has been constructed on the basis of Zienkiewicz’s triangle. A mixed approximation is used for the plate deflection and turning angles. It is shown that with a decrease in the triangle dimensions the mixed approach ensures convergence both for the plate deflection and the bending moments, which is practically independent of the way the plate is split into triangular elements. In the problems on free vibrations and stability of plates, the mixed approach yields more exact values of the eigenfrequencies and critical loads as compared to a classical Zienkiewicz’s triangle. The results of the numerical analysis of the convergence and accuracy of the solutions to a number of test problems on bending, free vibration, and stability of a square plate are presented. __________ Translated from Problemy Prochnosti, No. 4, pp. 108–122, July–August, 2008.     

Reduced graphene oxide supported palladium–silver bimetallic nanoparticles for ethanol electro-oxidation in alkaline media

Palladium–silver bimetallic nanoparticles loaded on reduced graphene oxide (Pd–Ag/RGO) were prepared by co-reduction of mixed metal salts and graphene oxide (GO) with urea-assisted ethylene glycol (EG). The as-obtained Pd–Ag/RGO nanocomposites were characterized by X-ray diffraction, transmission electronic microscopy, and UV–Vis absorption spectroscopy. The results show that the nanoparticles with an average particle size of 5 nm are dispersed on the surface of RGO highly uniformly, besides the Pd–Ag bimetallic nanoparticles are more helpful to promote the reduction of GO than monometal ones. The electrochemical activities of the as-prepared nanocomposites for ethanol oxidation were investigated by using cyclic voltammetry and chronoamperometry in alkaline solution. Compared to the Pd–Ag/E-tek carbon (Pd–Ag/C) and Pd–Ag/multi-walled carbon nanotubes (Pd–Ag/MWCNTs) which were fabricated by the same method, the Pd–Ag/RGO exhibit much higher electrocatalytic activity, stronger tolerance to CO and better stability during the ethanol electro-oxidation reaction in alkaline media. The electrocatalytic performances of Pd–Ag/RGO with different mass ratios of Pd–Ag toward ethanol oxidation in alkaline media were also studied. The results indicate that the electrocatalytic activity of Pd–Ag/RGO with 1:1 mass ratio of Pd–Ag is the best.     

Stability of plates from a granular composite with physically nonlinear inclusions and a damageable matrix

We present formulation and solution of the problem on the bifurcational stability of rectangular plates from granular composites with a damageable matrix and physically nonlinear inclusions. Translated from Problemy Prochnosti, No. 2, pp. 91–101, March–April, 2009.     

Equipment for the Spectral Characterization of High-Temperature Particles

The spectral radiant characteristics of plume particles of a solid rocket engine are important in the design of the engine specific impulse, ablative material, and plume flame hiding. These parameters are measured from tests of the engine. Some equipment has been established to realize particle heating, uniform particle distribution, and measurements based on an FTIR spectral instrument. The equipment is based on SiC heating and is divided into a warm-up chamber and a measurement chamber to improve the particle temperature stability. A special design of uniform particle distribution combined with an acoustic levitation device is used to determine the particle falling speed. The spectral characteristics and the transmission rate of the particles have been measured by using the system including a standard blackbody, an assembled optical system, and an FTIR spectrometer. The measurements of particle concentration and temperature are given in detail. The instrument specifications are as follows: temperature range – 60–1500 °C; spectral range – 0.60–25 μm; and particle dimension range – 10–500 μm. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Density functional study of structural and electronic properties of GaPn (2?≤?n?≤?12) clusters

Low-lying equilibrium geometric structures of GaP _n (n = 2–12) clusters obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied within the local spin density approximation (LSDA) and the three-parameter hybrid generalized gradient approximation (GGA) due to Becke–Lee–Yang–Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static dipole polarizabilities are calculated for the ground-state structures within the GGA. It is observed that the gallium atoms of the symmetric ground-state structures prefer to occupy the peripheral positions. It is found that the relative ordering of the isomers is influenced by the nonlocal exchange-correlation effects for small clusters. Generalized gradient approximation extends bond lengths and widens the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), as compared to the LSDA gap. The odd–even oscillations in the dissociation energy, the second differences in energy, the HOMO–LUMO gaps, the ionization potential, the electron affinity, and the hardness are more pronounced within the GGA. The stability analysis based on the energies clearly shows the GaP₅ and GaP₇ clusters to be endowed with special stabilities.     

Stability of orthotropic thin-walled cylindrical shells under torsion. Part 2. Experiment

We present the results of experimental studies of stability of thin-walled orthotropic cylindrical shells in torsion. The classical solution and the refined theoretical solution as derived in Part 1 are compared with experimental data. Some general conclusions have been made, which define more precisely the current notions of shell buckling under torsion. __________ Translated from Problemy Prochnosti, No. 4, pp. 69–78, July–August, 2008.     

Tuning the stress induced martensitic formation in titanium alloys by alloy design

Two novel titanium alloys, Ti–10V–2Cr–3Al and Ti–10V–1Fe–3Al (wt%), have been designed, fabricated, and tested for their intended stress-induced martensitic (SIM) transformation behavior. The results show that for Ti–10V–1Fe–3Al the triggering stress for SIM transformation is independently affected by the β domain size and β phase stability, when the value of the molybdenum equivalent is higher than ~9. The triggering stress was well predicted using the equations derived separately for the commercial Ti–10V–2Fe–3Al alloy. For samples containing β with a lower molybdenum equivalence value, pre-existing thermal martensite is also present and this was found to have an obstructive effect on SIM transformation. In Ti–10V–2Cr–3Al, the low diffusion speed of Cr caused local gradients in the Cr level for many heat treatments leading even to martensite free zones near former β regions.