Temperature dependence of the thermophysical properties of a Teflon — Bronze antifriction material

The effect of temperature and the concentration of the dispersed metallic filler on the thermophysical properties of a Teflon-based composition have been experimentally investigated. The results of the measurements of the thermophysical characteristics of the filled and unfilled Teflon are evaluated with allowance for the thermal conductivity of the components, their physicochemical interaction, and the change in the structure of the heterogeneous systems investigated.Deceased.A. M. Gor'kii Kiev State Pedagogical Institute; Institute of Colloidal Chemistry and the Chemistry of Water, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 6, pp. 1053–1056, November–December, 1971.     

Stressed state of an elastoplastic isotropic shell with a through crack with regard for material hardening

We have solved the problem of determining the stressed state of an elastoplastic isotropic shell of arbitrary curvature with a through crack with regard for material hardening. We have obtained a system of singular integral equations and solved it numerically by the method of mechanical quadratures. We have also studied the influence of material hardening on the general characteristics of the stressed state.     

Modeling,simulation and validation of material flow on conveyor belts

In this paper a model comparison approach based on material flow systems is investigated that is divided into a microscopic and a macroscopic model scale. On the microscopic model scale particles are simulated using a model based on Newton dynamics borrowed from the engineering literature. Phenomenological observations lead to a hyperbolic partial differential equation on the macroscopic model scale. Suitable numerical algorithms are presented and both models are compared numerically and validated against real-data test settings.     

Biaxial tension of a homogeneous isotropic plate with two equal coaxial cracks with regard for plastic zones near their tips

We investigate the problem of determination of the stress-strain state of an isotropic plate with two equal cracks at a set homogeneous field of forces at infinity. It is assumed that the lips of the cracks are free of load and that, near their tips, plastic zones are formed. Using Kolosov–Muskhelishvili complex potentials, we seek a solution of the problem in the class of functions bounded at the tips of the cracks and reduce it to problems of linear conjugation. Relations for the determination of the values of plastic zones and crack tip opening displacements are obtained. We perform a numerical analysis of the problem and construct graphs of dependences of the lengths of plastic zones and crack tip opening displacements on the distance between the centers of the cracks.     

Existence and stability for a visco‐plastic material with a fractional constitutive equation

The well posedness of the evolutive problem for visco‐plastic materials represented by two different fractional constitutive equations is proved. We show that, for these materials, we can observe permanent deformations. So that, as it is usual in plasticity, when the stress goes to zero, then the strain assumes a constant nonzero behavior. Moreover, we prove the compatibility of our models with the classical laws of thermodynamics. For the second model, described through a fractional derivative with an exponential kernel, we obtain the exponential decay of the solutions by means of the semigroup theory.     

Relation between the vectors Э and S for a plastic material with a sequence of ray-like loading paths

Two different complex loading paths are investigated in stress space — longitudinal tension with subsequent total unloading and reloading in transverse tension or compression. For these loading paths the local strains theory [4] is used to determine the values of the components of the strain vector {₁, ₂} in five-dimensional space for nonlinearities n=3 and n=5 together with the components of the stress vector S{S₁, S₂}. A relation between the vectors and S is established in terms of the given loading parameter k.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 241–245, March–April, 1970.     

Effect of ultrasound on the properties of a glass-reinforced plastic

It is shown that removing paraffin size from the glass strands by means of ultrasound has little effect on their strength, improves the structure of the material, and raises the mechanical strength of the GRP by 11–12%. An ultrasonic strand cleaner employing focusing piezoelectric ceramic transducers is described.Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 3, pp. 546–548, May–June, 1969.     

Identification of plastic material parameters with error estimation

In recent years, inverse analysis has become a common approach to typical engineering problems such as model identification. In this contribution, the inverse problem is discussed in light of taking experimental uncertainties into account. This involves in particular the propagation of experimental errors and the analysis of the sensitivity of the model response to variations in the model parameters to be determined. The method is applied to an elasto-viscoplastic material model which is used in the context of electromagnetic high-speed forming. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Free oscillations of plastic structures taking into account the elastic and damping properties of the material

The problem of the free oscillations of a plastic bar with a weight at one end is examined. A method is proposed for calculating the free oscillations of plastic structures, taking into account the special elastic properties and hysteresis losses of plastics. The original equation for the motion of the system, simplified by certain transformations and assumptions, is solved to a first approximation by the Krylov-Bogolyubov asymptotic method (following G. S. Pisarenko). The calculated data are in good agreement with the experimental findings.Mekhanika polimerov, Vol. 1, No. 1, pp. 136–145, 1965     

Anisotropy in the flow processes of a thin plastic layer

The theory of the flow of a thin layer of plastic material over surfaces developed by Il’yushin is extended to the case of an anisotropic ideally plastic material and anisotropic flow on the surface. Particular attention is given to determining the contact pressure. Two methods are proposed for solving this problem: a variational method and reduction to a Cauchy problem. The effect of anisotropy is revealed using specific examples.     

Modeling the creep stability of plastic shells

The problem of modeling the creep stability of shells is investigated on the basis of the strain compatibility, equilibrium and physical equations, and the boundary conditions. The mechanical similarity of physically nonlinear elastic and elasto-hereditary materials is examined in detail. The concept of an elastic potential and Volterra-type integral relations with increasing multiplicity are employed.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1059–1063, November–December, 1969.     

Modeling partial Greeks of variable annuities with dependence

Dynamic hedging used to mitigate the financial risks associated with large portfolios of variable annuities requires calculating partial dollar deltas on major market indices. Metamodeling approaches have been proposed in the past few years to address the computational issues related to the calculation of partial dollar deltas. In this paper, we investigate whether the additional complication of modeling the dependence between the partial dollar deltas improves the accuracy of the metamodeling approaches. We use several copulas to model the dependence structures of the partial dollar deltas and conduct numerical experiments to compare different metamodels. Despite the evidence of strong dependence in the estimated models, our numerical results show that modeling the dependence structures in the metamodels does not improve the accuracy of the estimations at the portfolio level. This is because the dependence between the partial dollar deltas is well captured by the covariates used in the marginal models. This finding suggests that we should focus more on marginal models than specifying the dependence structure explicitly.     

Mechanical properties of a hollow-fiber glass-reinforced plastic

The strength and elastic properties of a hollow-fiber glass-reinforced plastic are investigated together with the effect of temperature, and long-time and cyclic loading on its mechanical characteristics. The instantaneous moduli of elasticity and the creep kernel parameters are obtained on the basis of the creep diagrams.Translated from Mekhanika Polimerov, No. 2, pp. 341–345, March–April, 1971.