Dynamic properties of teflons obtained under various molding conditions

The natural frequencies and decrements, velocities of sound, dynamic moduli of elasticity, and Poisson's ratios of teflon specimens have been investigated in relation to the nature of the starting powder and molding conditions. The optimal dynamic characteristics are determined and it is shown that chey can be used to optimize the molding conditions and control the quality of teflon products.Mekhanika Polimerov, Vol. 2, No. 6, pp. 917–922, 1966     

Influence of technological processing parameters on the properties of carbon filled thermoplastics

The effect of processing parameters of injection molding on the mechanical and tribotechnical properties of carbon plastics based on polyacetals is investigated. The copolymer of 1,3,5-trioxane with 1,3-dioxolane is used as the polymer matrix. Hydrated cellulose Ural LO-24 carbon fibers are used as the reinforcing filler. The effect of molding temperature, pressing time, and temperature of the casting mould on the properties of carbon plastics is investigated. It has been found that for improving the mechanical properties of carbon plastics it is necessary to raise the molding temperature up to 200–210°C. Prolongation of the technological cycle leads to thermal degradation of the polymer in the cylinder of a casting machine. The mould temperature only slightly affects the composite strength properties, but lower temperatures create better conditions for polymer crystallization. As a result of our investigations, the optimal processing parameters of the above carbon plastics are determined.Ukrainian State University of Chemical Technology, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 3, pp. 385–392, 1999.     

Effect of the nature of the filler surface on the properties of phenol-formaldehyde molding powders

The physicomechanical properties and microstructure of phenolic molding powders containing fillers with different surface energies have been investigated. It has been found that an increase in filler surface energy leads to an increase in the density of the resin around the filler particles and hence to an improvement in the physicomechanical properties of the molding powder. A parallel investigation of a molding powder containing a lubricant shows that adsorption of the lubricant on the filler surface reduces the density of the resin, which is accompanied by a deterioration in the properties of the material.Scientific-Research Institute of Precision Engineering Moscow. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 677–681, July–August, 1968.     

Effect of process parameters on injection compression molding of pickup lens

The residual stresses and shrinkages of pickup lens in injection compression molding are investigated in this study. It was realized that the behavior of residual stresses in injection compression molding parts was affected by different process conditions such as melt temperature, mold temperature, compression pressure and time. Moldings under different conditions were numerically investigated to study the effects of the process conditions on the residual stresses and shrinkage of a pickup lens with large thickness variations. The mold temperature and compression were found to be the most important factors that affect the shrinkage of lens in the thickness direction, resulting in surface profile deviation. The effect of heat transfer coefficient of the mold wall used in the molding simulation was also discussed.     

Concerning the strength and fracture of thermally aged polycarbonate

The change in the strength, fractography, and supermolecular structure of polycarbonate after thermal aging has been experimentally investigated. It is shown that the fall in the strength of the polycarbonate after aging (T 160°C) is chiefly related with the formation of dangerous defects as a result of the destruction of the supermolecular structure at the surface of the block. It is noted that under the same conditions there is some ordering of the supermolecular structure of the polycarbonate at depths of 150 µ or more, but this has practically no effect on the strength characteristics.Institute of Physicotechnical Problems of Energetics, Academy of Sciences of the Lithuanian SSR, Kaunas. Translated from Mekhanika Polimerov, No. 5, pp. 951–952, September–October, 1971.     

Iterative processes based on block <Emphasis Type="Italic">H</Emphasis>-splittings

Block H-splittings of block square matrices (which, in general, have complex entries) are examined. It is shown that block H-matrices are the only ones that admit this type of splittings. Iterative processes corresponding to these splittings are proved to be convergent. The concept of a simple splitting of a block matrix is introduced, and the convergence of iterative processes related to simple splittings of block H-matrices is investigated. Multisplitting and nonstationary iterative processes based on block H-splittings are considered. Sufficient conditions for their convergence are derived, and some estimates for the asymptotic convergence rate are given.     

Mechanism of the increase in strength and heat resistance of oriented polymeric materials modified by graft copolymerization with vinyl monomers

The mechanical properties and structures of oriented films and fibers composed of polyethylene, polymethyl methacrylate, and other amorphous and crystalline polymers modified by the synthesis of uniformly distributed graft and block copolymers of methyl methacrylate, acrylonitrile, vinylidene chloride and other monomers have been the subject of a comparative investigation. The effect of the grafted polymers on the molecular mobility, relaxation processes, and solubility of the materials is explained by reference to a universal physical "crosslinking" mechanism. A theory of the interrelation between the structure and physical properties of the materials, the nature of the polymers, and the grafting conditions is developed and used to analyze the experimental data on a broad range of systems.V. I. Lenin Belorussian State University, Minsk. Translated from Mekhanika Polimerov, No. 6, pp. 968–975, November–December, 1973.     

Effect of processing conditions on the supramolecular structure and strength properties of polycaprolactam

The formation of supramolecular structures in block polycaprolactam is considered. It is shown that technological factors have a considerable effect on the nature of the supramolecular structure. Two of these factors are the temperature gradient of the polymer melt and the nature of its motion in the cylinder of the injection molding machine up to the moment of injection into the mold. It is shown that the nonuniformity of deformation and the considerable number of defects associated with large supraspherulitic formations lead to a deterioration in the strength and deformation properties of polymers.Mekhanika Polimerov, Vol. 2, No. 5, pp. 659–663, 1966     

On the connectedness of partially balanced block designs

The necessary and sufficient conditions for m-associate partially balanced block (PBB) designs to be connected are given. This generalizes the criterion for m-associate partially balanced incomplete block (PBIB) designs, which has originally been established by Ogawa, Ikeda and Kageyama (1984, Proceedings of the Seminar on Combinatorics and Applications, 248–255, Statistical Publishing Society, Calcutta).This work was partially supported by the Polish Academy of Sciences Grant No. MR I.1-2/2.     

Optimization of the injection molding process for short-fiber-reinforced composites

A fast and effective methodology integrating the finite-element and Taguchi methods is presented to determine the optimal design conditions of the injection molding process for short-fiber-reinforced polycarbonate composites. The finite-element-based flow simulation software, M-flow, was employed to simulate the molding process to obtain the fiber orientation distributions required. The Taguchi optimization technique was used to identify the optimal settings of injection molding parameters to maximize the shear layer thickness. The effects of four main parameters — the filling time, melt temperature, mold temperature, and injection speed — on the fiber orientation or the shear layer thickness were investigated and discussed. It is found that the dominant parameter is the filling time. The best levels of the four parameters to acquire the thickest shear layer are also identified.     

Exact formulae and matrix-less eigensolvers for block banded symmetric Toeplitz matrices

Precise asymptotic expansions for the eigenvalues of a Toeplitz matrix \(T_n(f)\), as the matrix size n tends to infinity, have recently been obtained, under suitable assumptions on the associated generating function f. A restriction is that f has to be polynomial, monotone, and scalar-valued. In this paper we focus on the case where \(\mathbf {f}\) is an \(s\times s\) matrix-valued trigonometric polynomial with \(s\ge 1\), and \(T_n(\mathbf {f})\) is the block Toeplitz matrix generated by \(\mathbf {f}\), whose size is \(N(n,s)=sn\). The case \(s=1\) corresponds to that already treated in the literature. We numerically derive conditions which ensure the existence of an asymptotic expansion for the eigenvalues. Such conditions generalize those known for the scalar-valued setting. Furthermore, following a proposal in the scalar-valued case by the first author, Garoni, and the third author, we devise an extrapolation algorithm for computing the eigenvalues of banded symmetric block Toeplitz matrices with a high level of accuracy and a low computational cost. The resulting algorithm is an eigensolver that does not need to store the original matrix, does not need to perform matrix-vector products, and for this reason is called matrix-less. We use the asymptotic expansion for the efficient computation of the spectrum of special block Toeplitz structures and we provide exact formulae for the eigenvalues of the matrices coming from the \(\mathbb {Q}_p\) Lagrangian Finite Element approximation of a second order elliptic differential problem. Numerical results are presented and critically discussed.     

Pressure distribution in molding GRP parts of complex shape

This paper presents the results of an experimental study of the pressure distribution in the mold in molding parts consisting of cylindrical and conical components. The effect of the weight of molding compound introduced into the mold and the loading conditions on the pressure distribution is investigated. It is shown that the hypothesis of hydrostatic pressure transmission to the walls of the mold is incorrect in relation to the manufacture of glass-reinforced plastic (GRP) parts of complex shape.Mekhanika Polimerov, Vol. 1, No. 4, pp. 130–135, 1965     

Increasing the wear resistance of graphitoplast parts

The effect of compression molding conditions on the physicomechanical properties of graphitoplast is studied. The question of the correlation between the microstructure of the material and its wear resistance is considered. It is shown that in order to obtain optimal properties it is necessary to establish the proper compression molding conditions for each part, in particular, the molding pressure and its conditions of application.Mekhanika Polimerov, Vol. 1, No. 3, pp. 115–119, 1965     

New subclasses of block H-matrices with applications to parallel decomposition-type relaxation methods

The parallel decomposition-type relaxation methods for solving large sparse systems of linear equations on SIMD multiprocessor systems have been proposed in [3] and [2]. In case when the coefficient matrix of the linear system is a block -matrix, sufficient conditions for the convergence of methods given in [2], [3] have been further improved in [5] and [4]. From the practical point of view, the convergence area obtained there is not always suitable for computation, so we propose new, easily computable ones, for some special subclasses of block -matrices. Furthermore, this approach improves the already known convergence area for the class of block strictly diagonally dominant (SDD) matrices.     

On nonsymmetric saddle point matrices that allow conjugate gradient iterations

Linear systems in saddle point form are usually highly indefinite,which often slows down iterative solvers such as Krylov subspace methods. It has been noted by several authors that negating the second block row of a symmetric indefinite saddle point matrix leads to a nonsymmetric matrix ${{\mathcal A}}Linear systems in saddle point form are usually highly indefinite,which often slows down iterative solvers such as Krylov subspace methods. It has been noted by several authors that negating the second block row of a symmetric indefinite saddle point matrix leads to a nonsymmetric matrix whose spectrum is entirely contained in the right half plane. In this paper we study conditions so that is diagonalizable with a real and positive spectrum. These conditions are based on necessary and sufficient conditions for positive definiteness of a certain bilinear form,with respect to which is symmetric. In case the latter conditions are satisfied, there exists a well defined conjugate gradient (CG) method for solving linear systems with . We give an efficient implementation of this method, discuss practical issues such as error bounds, and present numerical experiments. In memory of Gene Golub (1932–2007), our wonderful friend and colleague, who had a great interest in the conjugate gradient method and the numerical solution of saddle point problems. The work of J?rg Liesen was supported by the Emmy Noether-Program and the Heisenberg-Program of the Deutsche Forschungsgemeinschaft.     

Investigation of the supermolecular structure of polyformaldehyde in an injection-molded block. I

The supermolecular structure of polyformaldehyde has been investigated in an injection-molded block. This structure is a complex one in relation to the distribution of spherulites of various sizes and the ordering of the spherulites within the block.Mekhanika Polimerov, Vol. 4, No. 2, pp. 205–209, 1968     

Wear resistance of cured epoxy-novolac compositions

It has been established that changing the elasticity of rigid crosslinked epoxy-novolac block copolymers changes the friction mechanism and wear characteristics. The optimal conditions for obtaining block copolymers with the greatest wear resistance have been determined. The results of testing epoxy novolacs in neutral and alkaline media are presented.Leningrad Lensovet Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1107–1109, November–December, 1969.     

Temperature dependence of E and tg δ for polymethylmethacrylate and polystyrene with different kaolin contents

The temperature dependence of the dynamic modulus of elasticity E and the loss tangent tg has been investigated for polymethylmethacrylate (PMMA) and polystyrene (PS) with different contents of kaolin filler (K), in the glassy state and in the region of incipient devitrification. It is concluded that supermolecular reinforcing structures appear in filled polymers in which the intermolecular forces are sufficiently strong.Mekhanika Polimerov, Vol. 3, No. 5, pp. 854–857, 1967     

Effect of processing technology on the structure and properties of polypropylene

The methods of macro- and microstructural analysis are used to investigate the relation between the injection molding parameters, on the one hand, and the structure and physico-mechanical properties of the molded polypropylene block, on the other. It is shown that the structure takes the form of layers of different thickness and shape. Certain properties of molded products are determined not only by the spherulitic structure but also by the nature of the macrostructure of the polymer in the block.Voronezh Technological Institute. Translated from Mekhanika Polimerov, No. 2, pp. 200–204, March–April, 1971.     

Geometrical constructions of class‐uniformly resolvable structure

We use arcs, ovals, and hyperovals to construct class‐uniformly resolvable structures. Many of the structures come from finite geometries, but we also use arcs from non‐geometric designs. Most of the class‐uniformly resolvable structures constructed here have block size sets that have not been constructed before. We construct CURDs with a variety of block sizes, including many with block sizes 2 and 4. In addition, these constructions give the first systematic way of constructing infinite families of CURDs with three block sizes. © 2011 Wiley Periodicals, Inc. J Combin Designs 19:329‐344, 2011