Spinel fibers for ceramics

The process of formation of a fibrous spinel in the Al₂O₃–MgO system is investigated. The dependences of the spinel structure and properties on technological parameters of the process of synthesis is studied. Optimal relations between the fiber constituents for obtaining a stoichiometric spinel are determined and a two-stage mechanism of its formation has been found. Some ceramic materials are obtained from fibrous dispersions, and their physicomechanical characteristics have been estimated.Institute of General and Inorganic Chemistry, Belarus National Academy of Sciences, Minsk, Belarus. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 4, pp. 509–516, July–August, 1999.     

Electret composite materials based on polymers: Main properties and new fields of application

Data are given on the effect of an electret charge on wetting, spreading, sorption, and diffusion of liquids in polymers and composites. The modification of polymers in electric fields or by electret and electrochemically active fillers improves the physical-mechanical and tribological characteristics of materials. It is shown that the electret composites used in machines for protecting the metal-polymer joints against corrosion increase their rigidity and tightness and improve their tribological characteristics. Electret composites are new-generation materials (smart or intelligent materials) since they respond to recent developments in technology and are capable of raising the efficiency of machines with simultaneous reduction in energy and consumption of materials.Submitted to the 10th International Conference on Mechanics of Composite Materials, April 20–23, 1998, Riga, Latvia.Belyi Metal-Polymer Research Institute, National Academy of Sciences, Gomel 246652, Belarus. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 2, pp. 153–162, March–April, 1998.     

Effect of the molecular weight of polystyrene on the viscosity of concentrated solutions

The viscosity of solutions of polystyrene of various molecular weights (from 1.04 · 10² to 3.8 · 10⁵) in a poor solvent (decalin) and a good solvent (ethylbenzene) has been measured at temperatures from 15 to 70°C over a broad range of shear stresses from 10² to 10⁶ dyne/cm². The nature of the solvent has a considerable influence on the critical molecular weight and the absolute value of the viscosities of the solutions over the entire range of molecular weights and on the form of the flow curves of decalin solutions of polystyrene as a function of temperature. The heat of activation of viscous flow increases with increase in molecular weight and shear stress on the interval 20–80°C. The results obtained are explained in terms of the effect of the molecular weight of the polymer, the nature of the solvent, stress and temperature on structure formation in the solution and on the orientation of the macromolecules and structures in the flow process.Ural Gor'kii State University, Sverdlovsk. Translated from Mekhanika Polimerov, No. 5, pp. 920–926, September–October, 1970.     

Features of rheological and electrophysical properties of compositions based on polyvinyl alcohol and carboxymethylcellulose

A study has been made of the rheological and electrophysical properties (conductivity and dielectric loss angle) of aqueous solutions of polyvinyl alcohol (PVA), water-soluble carboxymethylcelluloses (Na-CMC), and compositions based on PVA and Na-CMC or methylcellulose, with PVA solution concentration 1% to 10% by weight and cellulose ether content in the polymer mixture up to 50% by weight. It was found that anisotropic structures can be formed in solutions based on PVA compositions under the influence of an orienting mechanical field; this is related to the formation of structure-sensitive associates in solution in the form of complexes.Paper presented at the 9th International Conference on the Mechanics of Composite Materials, Riga, October 1995.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 6, pp. 742–753, November–December, 1995.     

Rate of resorption of polymeric implants in relation to biological fluid hydrodynamics

The dissociation of water-insoluble macromolecular complexes dissociating with the formation of soluble macromolecules is theoretically examined. The dissociation dynamics in static and open systems are compared (model media and the living organism, respectively). The effect of the rate of metabolic processes and the water-salt balance on the dissociation-association equilibrium in the organism is predicted. The effect of the tension in thread formed from a polycomplex on its life is analyzed for constant and relaxing stress. The use of the theory for predicting the resorption times of polymeric implants (sutures) in the living organism is demonstrated.Paper presented at the First All-Union Conference on Engineering and Medical Biomechanics, Riga, October, 1975.All-Union Scientific-Research Institute of Medical Polymers, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 740–743, July–August, 1975.     

Statically equivalent solutions for assessment of refined plate theories

The Pagano exact solution for an infinite plate on a simple support is extended in such a way that artitrary boundary conditions can be prescribed. Based on Bufler's approach, the solution is obtained with a modified Fourier transformation that leads to a set of ordinary inhomogeneous differential equations. It can be shown that the Pagano solution is included as a special case of periodic boundary conditions, whereas the effect of nonperiodic boundary conditions is represented by particular terms. Statically equivalent solutions for the assessment of refined plate theories are derived, and the difference between simply supported and periodic boundary conditions is discussed.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Otto-von-Guericke Universität Magdeburg, Germany. Institut für Werkstoffwissenschaften, Martin-Luther-Universität Halle-Wittenberg, Germany. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 461–476, July–August, 1998.     

Numerical Integration of Reaction–Diffusion Systems

Approximating numerically the solutions of a reaction–diffusion system in an efficient manner requires the application of implicit methods, since the Courant–Friedrichs–Lewy condition on explicit methods imposes a time step of the order of the square of the space step. In this article, we review two types of strategies which are expected to yield reasonably precise solutions within a reasonable computing time. The first examines methods for solving the linear step necessary in any resolution procedure; estimates of CPU time in terms of the error are given in the non preconditioned and in the preconditioned case – provided that it is possible to define an efficient preconditioner. The second strategy is based on splitting, with or without extrapolation. The respective faults and qualities of both strategies are examined; they lead to a list of difficult analytical and numerical problems with possible hints as to their solution.     

Second-approximation shear theory for shallow layered shells and plates

Analysis of a second-approximation refined shear model for shallow layered composite shells and plates with a substantially inhomogeneous structure over the thickness is presented. The tangential displacements and corresponding normal stresses are expressed in the form of a polynomial of the fith degree in the transverse coordinate and contain squared rigidity characteristics. In this way, the accuracy of results and practical coincidence with the 3D solutions is ensured. Based on the refined model, a theory of shallow layered shells is developed. A system of resolving equations of sixteenth power together with appropriate boundary conditions was obtained and solved analytically. It is shown that the area of application of the formed model is extended as compared with the model of the first approximation. The model proposed allows us to examine the stress-strain state of layered composite structures of substantially different thickness and physical-mechanical characteristics of the layers, including the possibility of simulating relatively large shear deformations of rigid layers separated by a low-modulus thin interlayer pliable to transverse shear.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Ukrainian Transport University, Kiev, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 363–370, May–June, 1998.     

Sandwich plates-free vibrations and damping analysis

A new analytical approach to the optimization analysis of stacking sequences of sandwich plate faces is presented. FRP faces are assumed to be constructed of 0₂°, 90₂°, and ±45° plies. A new set of design variables was succesfully used for the optimization analysis of natural flexural vibrations and modal loss factor of sandwich plates with FRP faces. In addition, the influence of the core thickness on optimization solutions was studied. Three variants of plate theories were considered, namely those of Love-Kirchhoff and first- and higher-order transverse shear deformation. To verify the results of the models proposed, the values of the natural vibrations were compared with the results obtained using the NISA II FEM package.Submitted to the 10th International Conference on Mechanics of Composite Materials, April 20–23, 1998, Riga, Latvia.Institute of Mechanics and Machine Design, Cracow University of Technology, 31–155, Cracow, Poland. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 2, pp. 276–286, March–April, 1998.     

Experimental study of fracture toughness and energy in composite materials

The paper presents an experimental investigation of fracture characteristics of composite materials. The post-peak response of the load-crack opening displacement of notched specimens is used to evaluate the fracture energy associated with progressive matrix damage and crack growth. Effects of fiber orientation and other geometric characteristics on fracture parameters are studied. The load versus crack opening displacement as well as crack length, fracture toughness, and energy versus the number of loading cycles are obtained for different specimens. Based on the experimental results of this study, concepts of the fracture mechanics are applied to evaluate the evolution of fracture toughness and energy.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Department of Mechanical & Industrial Engineering, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 323–332, May–June, 1998.     

Temperature dependence of the mechanical properties of polymers of different chemical structure in the temperature range from 4.2 to 300°K

Conclusions 1. The temperature dependences obtained for the ultimate alongation, tensile strength, and elastic modulus of various polymers showed that the relationship between the mechanical properties and chemical structure of macromolecules found in our earlier work at 4.2°K is retained at 78°K and, possibly, up to 90°K.2. It was shown that the passage of the tensile strength through a maximum upon warming from 4.2°K results from a corresponding increase in deformability, which is accompanied by a decrease in the elastic modulus and deviation of the polymer bodies from Hooke's law progressively with increasing temperature.3. It was shown that the amorphization of crystallizing polymers, for example, by quenching, gives a marked change in the deformability, tensile strength, and elasticity of the polymer body over the entire range from 300 down to 4.2°K.4. Study of the mechanical properties of polymers at 78°K in a helium medium and liquid nitrogen showed a marked effect of contact of the polymer with liquid nitrogen on these properties. This effect is different for polymers of varying chemical structure as well as for the same polymer in different physical states.Report presented at the Third All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1976.L. Ya. Karpov Scientific-Research Institute of Physical Chemistry, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 387–391, May–June, 1977.     

Effect of technological factors on the structure and properties of Eskaplen film material

The effect of the composition of the solvents, the concentration of the solutions, and the rate of film formation on the structure and properties of Eskaplen film material obtained on the basis of SKI-3 isoprene rubber hydrochloride has been investigated. The properties of the film material are shown to depend on the structure that develops during the film-forming process.Moscow Technologic Institute of the Meat and Dairy Industry. Translated from Mekhanika Polimerov, No. 1, pp. 8–13, January–February, 1973.     

Spectra of pressure relaxation times of polymer and copolymer melts and their practical use

The possibility of using pressure relaxation of melted polymers for the investigation of the structure of three types of polymers and their compositions and the analysis of the change of their molecular characteristics during aging is shown.Kazan State Technological University, Tatarstan, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 531–538, July–August, 1998.     

Structural damage accumulation and stable postcritical deformation of composite materials

The macroscopic failure of composite materials is preceded by complex multilevel processes accompanied by accumulation and localization of damaged centers and formation of a failure cluster. Therefore, the study of these mechanisms is one of the basic problems for the mechanics of modern composite materials used in aerospace engineering. The formation of a theory of the stable postcritical deformation of the work-softening media is considered. The pseudo-plastic deformation affected by structural damage of granular composites is investigated within the framework of the considered two-level structurally phenomenological model of heterogeneous media. The stable evolution of the interconnected processes is accompanied by stress redistributions, partial or complete unloading, and strain or damage localization that are one of the main causes of implementation of the postcritical deformation stage. The numerical calculation results of inelastic deformation and failure of the periodic unidirectional fiber-reinforced composites are presented under conditions of the displacement-controlled transverse proportional loading mode. The main mechanisms of the work-softening behavior for the indicated type of materials are described in the macro-homogeneous stress-strain states. Macroscopically, the failure of heterogeneous media as a result of postcritical deformation and the loss of stability of damage accumulation depends on the stiffness of the loading system. When a deformable body is fixed on the closed surface with sufficiently but not infinitely large coefficients of stiffness, it is possible to observe the equilibrium development of the localized volumes of work-softening and damage. The constitutive equations for the work-softening isotropic, transverse isotropic, and orthotropic media are presented. The effect of the loading system on the stability of deformation, damage accumulation, and failure under monotone and nonmonotone triaxial loading was studied. The growth of failure strains with increase in stiffness of the loading system and unequal resistance of heterogeneous body are registered and investigated. A preventive unloading method is offered for the mathematical modeling of the damage accumulation during the testing of the materials on the servo-controlled systems. The displacement-controlled mode is simulated by a series of soft loading and unloading cycles. The detected phenomenon of failure where the unloading leads to stress-strain diagrams with a negative slope of the descending branch was not found either in the displacement or stress-controlled monotone loading mode.Submitted to the 10th International Conference on Mechanics of Composite Materials, April 20–23, 1998, Riga, Latvia.Perm' State Technical University, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 2, pp. 234–250, March–April, 1998.     

Flow of a nonlinear viscoelastic liquid in cylindrical channels

The problem of nonrectilinear steady-state flow of a nonlinear viscoelastic liquid in an arbitrary cylindrical channel is examined. On the assumption that the cross flows are insignificant as compared with the longitudinal flows an equation of state is derived for the flow regime in question. A variational principle established for steady-state flows of the investigated media is proposed as the basis of a method of solving problems of the flow of polymer materials in arbitrary cylindrical channels. The flow of a polymer solution in rectangular channels is investigated.Institute of Mechanics, AS UkrSSR, Kiev. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1103–1111, November–December, 1968.     

Effect of fillers and solvents on the properties of polystyrene coatings

The mechanism of coating formation from solutions of atactic polystyrene in xylene and carbon tetrachloride has been investigated. It has been established that, as the filler content increases, in coatings formed from polystyrene solutions containing an evaporating solvent the growth of the internal stresses and the thermophysical characteristics is characterized by similarity of slope, as distinct from the case of coatings obtained from systems containing a polymerizing solvent. It is shown that the nature of the solvent has an important effect on the character of the interaction at the polymer—filler interface and on the structure and properties of the coatings.Kucherenko Central Scientific-Research Institute of Structural Design. Institute of Physical Chemistry, AS USSR, Moscow. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1127–1129, November–December, 1968.     

Wood-filled thermoplastic composites

Different physical properties of wood-filled thermoplastic materials produced by a special mixing and extrusion process are examined. The results show that the wood content and the kind of plastics are the main parameters that control the physical properties of composites. In general, wood-filled thermoplastic materials exhibit mechanical properties comparable to those of customary wood fiber products, i.e., medium density fiberboard (MDF); however, they show distinctly better behavior than the MDF and natural wood after exposure to moisture.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Universität Kassel, Institut für Werkstofftechnik, Kunstoff-und Recyclingtechnik, Mönchebergstraße 3, 34109 Kassel, Germany. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 795–802, November–December, 1998.     

Identification of mechanical properties of composites based on design of experiments

A numerical-experimental method for the identification of mechanical properties of laminated polymeric composites from the experimental results is being developed. For the first time, it is proposed to use the method of experiment planning to solve the identification (inverse) problems. The basic idea of the approach is that simple mathematical models are determined only from information on the response of a structure in reference points of the design. Therefore, a significant reduction in the calculation of the identification functional (about 50–100 times) can be achieved in comparison with the conventional methods of minimization. Examples of the numerical identification of the elastic properties of the laminated composites from the measured eigenfrequencies of plates are discussed.Submitted to the 10th International Conference on Mechanics of Composite Materials, April 20–23, 1998, Riga, Latvia.Institute of Computer Analysis of Structures, Riga Technical University, Riga LV-1058 Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 1, pp. 3–16, January–February, 1998.     

Exact solutions with compact and noncompact structures for the one-dimensional generalized Benjamin–Bona–Mahony equation

This paper is devoted to analyzing the physical structures of nonlinear dispersive variants of the Benjamin–Bona–Mahony equation. It is found that these generalized forms give rise to compactons solutions: solitons with the absence of infinite tails, solitons: nonlinear localized waves of infinite support, solitary patterns solutions having infinite slopes or cusps, and plane periodic solutions. It is also found that the qualitative change in the physical structure of solutions depends strongly on whether the exponents of the wave function u(x, t) whether it is positive or negative, and on the speed c of the traveling wave as well.     

Flexible composites, strength, deformation, and fracture processes. 1. Reinforcement structures and tensile strength

Fiber-reinforced flexible composites are extensively used for different kinds of applications, for example, tubes, drive belts, tires, and coated fabrics. Typical for these materials are matrix materials allowing large strain deformation and reinforcement structures allowing bending. Apart from the tensile strength and limited bending stiffness, damage resistance and ductile-brittle transition characteristics are discussed. The tensile strength usually follows the rule of mixture. The mode of fracture and damage resistance, however, strongly depend on penetration of the matrix into the fiber bundles, textile structure, and internal friction. Models for the work of fracture and the ductile-to-brittle fracture transition are discussed.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 747–760, November–December, 1998.