An exact semi-analytic solution for residual stresses and strains within a thin hollow disc of pressure-sensitive material subject to thermal loading

There is considerable current interest in the development of constitutive equations for pressure-dependent plastic materials. In particular, in contrast to classical plasticity there is no commonly accepted relation to connect stress and strain or strain rate for such materials. Analytic and semi-analytic solutions are convenient to compare qualitative features of boundary value problems solved for different models. Such comparative studies can be useful to choose this or that model for specific applications. Analytic and semi-analytic solutions are also necessary to verify numerical codes. In the present paper, a new semi-analytic solution for a thin hollow disc subject to thermal loading is developed. A numerical method is only necessary to solve transcendental equations. The constitutive equations for connecting the plastic portion of the strain rate tensor and the stress tensor consist of the Drucker-Prager yield criterion and its associated flow rule. Therefore, the main distinguished feature of the solution is that the material is plastically compressible.     

Application of the united atom model for estimating the lifetime of negative molecular ions relative to electron autodetachment

A model proposed for describing the scattering of low-energy electrons (whose energy ranges between thermal energy and several electronvolts) from polyatomic molecules makes it possible to estimate the lifetime of shape resonances. The parameters of the model are determined by specific structural and experimental characteristics of molecules. The results of approximate computations of the lifetimes for negative ions of molecules with different symmetries (diatomic halogens, parabenzoquinone, fullerene C₆₀, benzothiadiazoles, anthraquinone derivatives, and substituted benzene forms) are presented. The obtained data show that the lifetimes are sufficient for the formation of fragment ions observed in the mass spectra of negative ions.     

Optimal temperature conditions of carbonaceous feedstock pyrolysis

A problem of optimal control of the temperature conditions of carbonaceous feedstock pyrolysis in a plug-flow reactor was formulated, and it was shown that the optimal temperature profile depends significantly on the ratio between the activation energies of the desired and side reactions and also on the type of the main pyrolysis reactions (consecutive, parallel, or consecutive-parallel).     

Nonwoven blend composites based on poly(3-hydroxybutyrate)–chitosan ultrathin fibers prepared via electrospinning

With the use of scanning electron microscopy, differential scanning calorimetry, and electron paramagnetic resonance, the structural–dynamic analysis of ultrathin fibrous matrixes based on poly(3-hydroxybutyrate) and blend composites of this polymer with chitosan is performed. It is shown that the addition of a small amount of chitosan causes change in the morphologies of the matrixes and leads to a marked increase in their melting enthalpies. It is found that the studied fibers contain amorphous regions with various morphologies. The dynamics of the spin probe TEMPO in these regions is investigated, and its change under the influence of increased temperature, an aqueous medium, and ozone is examined. The mechanism controlling the effects of chitosan, temperature, and an oxidative aggressive medium on the structuring of fibers is advanced.     

Plane strain extension of a strip made of a material with stress state type dependent properties and weakened by cuts with circular base

The limit properties of many heterogeneous materials such as grounds, concrete, ceramics, cast-iron alloys, and various heat-resistant and powder materials, as well as the properties of many composite materials, depend on the loading conditions. Neglecting the effects exhibited by such materials may result in nonconservative limit load analysis for some types of loading and possibly in an overly increased end product weight by failing to take into account stronger material properties for other types of loading. This paper presents a possible approach to modeling the behavior of such materials under plastic deformation, which is demonstrated for the sample problem on the extension of a strip weakened by cuts with circular base. An analytic solution on the basis of a rigid-plastic model of the material and a numerical solution by the finite elementmethod with elastic strains and small strengthening taken into account are presented.     

High amplitude dislocation damping in superconducting Pb and In

The amplitude dependence of ultrasound absorption due to dislocations, α, has been studied for single crystals of pure lead and indium as well as for lead doped with Tl, Sn or Bi, both in the superconducting and normal state and for a wide range of ultrasound amplitudes, ε₀. Pure and Tl-doped superconducting lead at large ε₀ displayed a maximum on the α(ε₀) dependence which became a plateau upon transition to the n-state. This is direct evidence for a change from static to dynamic dislocation hysteresis as a result of the increase in the electron drag constant. Limit values for the dislocation loop lengths have been estimated, viz. 2.4 × 10⁻⁴ cm < L_N < 10.4 × 10⁻⁴ cm. In other single crystals the dynamic hysteresis occurred both in the n- and s-state. In all the single crystals, α increased with the increase of ε₀ above the maximum amplitude and onset of the plateau which was observed in both states. The effect is associated with non-linear phenomena arising at significant loop flexures. The amplitude dependence of the losses due to this effect has been analysed, the results of the analysis being in good agreement with the experimental data.