Friction and wear of polymer-based composites

Polymeric materials containing different fillers and/or reinforcements are frequently used for applications in which friction and wear are critical issues. This overview describes how to design high temperature-resistant thermoplastics, e.g., filled with carbon fibers and internal lubricants, for operation under low friction and wear at elevated temperatures as sliding elements in, e.g., textile drying machines. Further information will be given on the systematic development of continuous fiber/polymer composites with high wear resistance, and on attempts for the prediction of their load-bearing capacity using a finite element approach. Finally, the application of such composites in thermoplastic filament-wound journal-bearings is discussed.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of Composite Materials (IVW), University of Kaiserslautern, D-67663 Kaiserslautern, Germany. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 717–732, November–December, 1998.     

Estimation of the molecular characteristics of polymers by the SPRT method and study of their influence on the properties of compositions

Pressure relaxation was examined in the cylinder of an MPT Monsanto processability tester after stopping the piston. The experimental function of the pressure drop F(t) was smoothed over and approximated by cubic splines. The spectra of pressure relaxation times (SPRT) were obtained according to the method of Schwarzl-Staverman. The SPRT method served well for estimating the spectra of the molecular-mass distribution (MMD) of polymers close in their physical sense to the SPRT. The correlation of the characteristic relaxation times and average molecular mass of ethylene-propylene rubbers and polyethylenes obtained by gel permeation chromatography was approximated by optimum models used for calculating the the molecular mass of rubbers according to the measurement results of the relaxation pressure of melts. The SPRT and characteristic relaxation times were used to analyze the significant technical properties of compositions based on polyethylene and rubber. The SPRT method was used to examine the failure of the cure network of butyl rubber and the dependence of the mechanical properties of thermoplastic elastomers on the molecular features of the decomposite.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Kazan State Technological University, Tatarstan, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 691–698, September–October, 1998.     

Properties of fillers and reinforcing fibers

Fillers have always played an important role in the plastics industry. Filled polymers form a specific class of composites, which are tending to replace many traditional materials. Various kinds of organic fillers are used. The experimental study of such nonconventional organic and inorganic fillers obtained from agricultural waste is presented to modify the properties of thermoplastics, such as pVC, HDPE, LDPE, and ABS. The properties obtained by using these fillers alone and in combinations show very interesting results, which are tabulated. The use of organic fillers should help lower the cost of many plastic products required in the building and agricultural industries.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Maharashtra Institute of Technology, Pune, India. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 651–663, September–October, 1998.     

Moduli of elasticity of polymer melts

The physical significance of the so-called initial modulus, determined in measuring the rheological properties of thermoplastic melts from the initial slope of the time dependence of the stresses at given constant shear rate, is considered. It is shown that this quantity is related with the ratio of the shear and normal stresses.Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 534–538, May–June, 1969.     

Structural approach to calculation of the effect of moisture on elastic characteristics of organoplastics

Data have been obtained for the structural calculation of the effect of moisture on the elastic characteristics of organoplastics from the properties of components. The distribution of moisture between the fiber and matrix — the components of a unidirectional composite — is considered. The elastic properties of the fiber are determined by an inverse calculation using the experimental dependences of the composite and matrix on moisture. The moisture effect on the properties of the materials is taken into account with influence functions, which differ by more than 25% for various characteristics. The results can be used for calculating the elastic properties of composites with various reinforcement schemes and at the nonequilibrium distribution of the moisture concentration in an actual environment.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of Polymer Mechanics, Riga, LV-1006, Latvia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 525–530, July–August, 1998.     

Averaging the physical properties of fibrous piezocomposites

Elastic, piezoelectric, and dielectric properties of fibrous composites with piezoelectric components are averaged for antiplane strains. Methods for determining coupled electroelastic fields in piezocomposites are proposed. Calculation results of the effective physical characteristics of some composites are given.Sumskii State University, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 1, pp. 116–123, January–February, 1998.     

Influence of ultradisperse additives on interaction of incompatible polymers

The influence of ultradisperse additives of -sialon and molybdenum disulfide on the interfacial boundary conditions of nitrile rubber containing 17–20% of acrylonitrile (SKN-18) and ultrahigh molecular-weight polyethylene (UHMWPE) is studied. The additives were introduced into the nonpolar UHMWPE, and then the modified composition was introduced into a crude rubber stock based on SKN-18. X-ray diffractometry, electron microscopy, and dynamic testing methods were used for studying the phase and supramolecular structure of the composition. A complex of physical and mechanical tests including the study of the wear and oil and cold resistance characteristics of the elastomeric compositions were carried out. It is shown that the use of ultradisperse additives allows us to improve the interaction at the SKN-18/UHMWPE interface and the operating properties of the materials.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of Nonmetal Materials, Siberian Branch, Russian Academy of Sciences, Yakutsk, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 803–810, 1998.     

Some aspects of the behavior of shock-compressed polymers

The changes in the properties of certain polymeric materials subjected to the action of plane shocks of varying amplitude are discussed. Three loading techniques are employed — single, multiple, and high-frequency multiple loading — each accompanied by a different rise in the temperature of the polymeric material. The results show that the change in physicomechanical properties also varies with the loading technique.Volgograd Polytechnic Institute. Translated from Mekhanika Polimerov, No. 1, pp. 76–80, January–February, 1970.     

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.     

Numerical identification of properties of particle-reinforced composite materials

The paper deals with numerical identification of the average elastic properties of particle-reinforced composite materials. The finite element method for the determination of deformation energy of the characteristic volume element was used. In earlier analytical investigations, an approximation function of the averaged elastic properties of the composite was derived. An identification procedure allows the estimation of the unknown approximation parameters from numerical experiments. The obtained functions describe precisely the numerical data for any relationships between constituents of the material.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of Computer Analysis of Structures, Riga Technical University, Riga PDP-1658, Latvia. Institute of Materials Science, Department of Materials Science, Martin-Luther-University Halle-Wittenberg, D-06099 Halle, Germany. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 383–390, May–June, 1998.     

Regulation of the mechanical properties of thermoplastic carbon fiber-reinforced plastics by changing their production conditions and surface treatment of the fibers

The effect of technological parameters of processing and surface treatment of carbon fibers on the mechanical properties of carbon fiber-reinforced plastics (CFRPs) was investigated. The copolymer of 1,3,5-trioxane with 1,3-dioxolane was used as the polymer matrix, and medium-modulus hydrated cellulose Ural LO-24 carbon fibers served as the reinforcing filler. The polymer matrix was mixed with the carbon fibers by the method of combined extrusion. The dependence of the mechanical properties of CFRPs on the technological parameters of screw-disk extrusion was studied. It was found that the properties of the composites were greatly affected by the size of the working disk gap, the disk rotation rate, and the temperature in the zone of normal stresses. The surface of the carbon fibers was activated with atmospheric oxygen in the temperature range of 450–600°C, with mass loss of the fibers no greater than 3–4%. A 30–40% increase in the mechanical properties of the CFRPs was achieved. A decrease in the melt index of the 1,3,5-trioxane copolymer with 1,3-dioxolane reinforced with oxidized carbon fibers was observed, which should be taken into account in processing the composites into products. Introduction of carbon fibers in the 1,3,5-trioxane copolymer with 1,3-dioxolane allows us to increase the wear resistance and decrease the friction coefficient, which makes it possibile to use these materials in the friction units of machines and mechanisms, such as plain bearings, gears, and flange packings.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Ukrainian State University of Chemical Technology, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 673–682, September–October, 1998.     

High-temperature destruction of composite materials during intense heat and gasdynamical action

High-temperature destruction of polymer composite materials during interaction with gas flows has been investigated experimentally. The braking pressure of the flow varied from 5 to 25 MPa. The basic laws of the destruction under high pressure were established. The condition of thermomechanical destruction of the materials studied under a pressure of 15 to 25 MPa was determined. A physical model of the high-temperature destruction of polymer composite materials subjected to intense heat and gasdynamical action was developed.Scientific Research Institute of Applied Mathematics and Mechanics, Tomsk State University, Tomsk, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 1, pp. 107–115, January–February, 1998.     

Some problems in the application of statistical dynamics to shells manufactured from fibrous composites

On the basis of a statistical approach presupposing direct utilization of experimental data produced in modelling operations, a procedure is proposed for computational estimates on composite materials in which allowance is made for the initial defects, the variable properties of the material, and the conditions of use (physical medium). Experimental data on Plexiglas shells which confirm the practical applicability of the procedure are given. Questions relating to the design of tests on composite shells are discussed.Translated from Mekhanika Polimerov, No. 4, pp. 743–745, July–August, 1972.     

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.     

Creep prediction of a layered fiberglass plastic

The results of short-term creep tests of a layered glass fiber/polyester resin plastic in tension at angles of 90, 70, and 45° to the direction of the principal fiber orientation are presented. The applicability of the principle of time-temperature analogy for the prediction of long-term creep of the composite and its structural components is revealed. The possibility of evaluating the viscoelastic properties of the composite from the properties of structural components is shown.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 295–306, May–June, 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.     

Results from investigations into the antifrictional characteristics of a group of polymer compositions based on epoxide resins

The results are presented from comparative investigations into the antifrictional and mechanical properties of polymer compositions based on epoxide resins ÉD-5, ÉD-6, and fillers in the form of finely dispersed powders of polymeric materials [polyfluoroethylene, polycaproamide (Kapron B), polyethylene, graphite, sawdust], Babbitt metal B-83, and solidol US-2 grease. The investigations show that the above-mentioned materials are not inferior in their antifrictional characteristics to the widely used nonferrous metals (Babbitt B-83, TsAM 9-1.5, bronze OTsS 5-5-5). The rational regions of use of the investigated compositions are indicated.Rostov-on-Don Institute of Railroad Engineers. Translated from Mekhanika Polimerov, No. 1, pp. 87–90, January–February, 1972.     

Theoretical prediction of the properties of multicomponent reinforced materials

On the basis of a generalization of previously considered models of reinforced media solutions are constructed for problems of determining the effective parameters and internal stress, temperature, and electromagnetic fields with application to multicomponent reinforced materials. Special attention is paid to the construction of approximate relations for calculating the reduced characteristics of multicomponent materials from the given properties of the components, by means of which the problem of predicting the physical properties of new multiphase materials may be solved. The approximate equations for determining the parameters of two-component media of the oriented glass-reinforced plastic type, obtained by various authors, follow from these relations as a special case.Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 4, pp. 646–654, July–August, 1969.     

Structure-sensitive liquid flowable compositions based on polyvinyl alcohol and silicotungstic acid

Conditions of the formation of structure-sensitive liquid flowable media based on 1.5 and 10% aqueous solutions of polyvinyl alcohol containing silicotungstic acid and water-soluble carboxy-methylcellulose in the form of its potassium salt (Na-CMC) are examined. Rheological, optical, and dielectric relaxation methods revealed the formation of several types of interpolymer complexes in the examined liquid flowable media. This leads to the formation of associates and an increase in the molecular mobility of the macromolecules and their fragments. The structure and properties of the complexes depend on the composition of the media as well as the method of introducing polyacids. It was found that it was possible to control the structure of such solutions by applying a mechanical of magnetic field. The compositions obtained can be used for producing anisotropic light-, electric-, and heat-sensitive film materials, as well as sensors of different types.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of General and Inorganic Chemistry, Belarus Academy of Sciences, Minsk, Belarus. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 3, pp. 413–424, May–June, 1998.     

Quasistatic anti-plane motion in the simplest theory of nonlinear viscoelasticity

We consider a very simple model in the framework of differential viscoelastic materials which are isotropic and incompressible. In this model the Cauchy stress tensor is split in an elastic part and a dissipative part. The elastic part is derived from a strain-energy density function only of the first invariant of the Cauchy–Green strain tensor. The dissipative part is like the Navier–Stokes equations: linear in the stretching tensor with a constant viscosity parameter. For this model we provide some time and spatial estimates in the quasistatic approximations for the equations governing anti-plane shear motions. Several explicit examples for specific form of the strain energy are produced. Our results impose analytical restrictions on the mathematical properties of the strain energy to ensure a physical behavior in the creep and recovery experiments. Moreover, we show polynomial decay for the spatial behavior in the class of stress-hardening (or strain-stiffening) materials. For stress-softening materials a Phragmen–Lindelof alternative is proved.