Effect of residual stresses on the strength of oriented glass-reinforced plastics

The effect of structural residual stresses on the strength of a glass-reinforced plastic loaded along and across the fibers is investigated. It is established that the residual stresses lead to an increase in the strength of the glass-reinforced plastic across the fibers and to cracking of the polymer matrix in tension along the fibers, but have practically no effect on the combined deformation of the matrix and the fibers in compression.Moscow Ordzhonikidze Aviation Institute. Translated from Mekhanika Polimerov, No. 3, pp. 475–480, May–June, 1969.     

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.     

Elastoplastic deformations of metal pressure vessels reinforced with unidirectional glass-reinforced plastic

The design of cylindrical shells reinforced in the circumferential direction with high-strength elastic fibers is considered. The problem is solved on the basis of the deformation and flow theories. Relations are derived for the layer thickness required to obtain a structure of uniform strength and for the tension that must be applied to the glass tape during winding.Moscow Ordzhonikidze Aviation Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1069–1074, November–December, 1969.     

Rigidity and torsional strength of glass-fiber reinforced plastics EF-32-301 with satin and cord fillers

The deformability and torsional strength of glass-fiber reinforced plastic tubes as a function of the angle of reinforcement is discussed. Experimental data are given, and theoretical relationships are analyzed. The use of these relationships is proposed for the experimental data obtained.Moscow Aeronautical Institute. Translated from Mekhanika Polimerov, No. 3, pp. 555–558, May–June, 1974.     

Some laws of the elastic properties of oriented fibrous polymers and fibers

The author considers the results of calculations of the limiting values of the elastic properties (modulus of elasticity and load-extension diagram) of the main types of chemical fibers, using a model with "ideal orientation" of the molecules and the derived laws of deformation of polymer chains. A method is proposed for calculating the elastic properties of "ideally oriented" polymers from the velocity of propagation of an elastic deformation pulse and the effective density of the "skeletons" of the polymer chains. Values of the moduli of elasticity of the amorphous regions of the structure of oriented polymers are calculated. The calculated results are compared with experimental data on the elastic properties of fibers.Mekhanika Polimerov, Vol. 2, No. 1, pp. 34–42, 1966Paper read at the XIV All-Union Conference on High-Molecular Compounds, Oriented State.     

Current state and prospects for development of the physical theory of brittle strength of polymers

Various mechanisms of brittle fracture and theories of the time dependence of the strength of rigid polymers are examined. The effect of various types of mechanical losses (deformation, dynamical, surface) on polymer strength and life is analyzed. The principal shortcomings of Griffith's theory of strength are pointed out. From an examination of the two basic mechanisms of brittle fracture of polymers-nonthermal and thermal (thermal fluctuation)-it is concluded that the latter is the more important. A comparison is made of the fluctuation theory of polymer strength with new experimental data on polymethyl methacrylate, and the causes of the transition from brittle to nonbrittle fracture are discussed. The effect of molecular orientation on the strength of polymers is examined on the basis of the fluctuation theory of strength.Mekhanika Polimerov, Vol. 2, No. 5, pp. 700–721, 1966     

Structural theory of the strength of reinforced plastics

Conclusions In the present study, we developed structural criteria that make it possible to predict at the component level (polymer binder, fibers) and interface level the long-term strength of laminated reinforced plastics in a plane stress state. The proposed relations make it possible to evaluate the effect of the rheological properties of the components, their volume fractions, and the geometry of the structure of the laminated packet on the long-term strength of reinforced plastics. The relations also permit resolution of the inverse problem: efficiently design the structure of such materials for specific loading conditions.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 833–839, September–October, 1989.     

Numerical characteristics of the degree of anisotropy of the mechanical properties of materials

Conclusions 1. A unique procedure for determination of the numerical characteristics of the degree of anisotropy of the strength and deformation properties of materials is proposed.2. The concepts of the deformability surface and the anisotropy surface of the deformability permit representing graphically the deformation properties of materials.3. The system of integral characteristics of the mechanical properties of materials opens up new possibilities in connection with the analysis and optimization of different reinforcement schemes.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 601–609, July–August, 1978.     

Thermomechanical properties of spot-bonded nonwoven synthetic-fiber materials

The thermomechanical properties of spot-bonded nonwoven synthetic-fiber materials with a polymer binder have been investigated. The materials are composed of heterogeneous fibers, with low-melting polymers (binder) forming the surface layer. The change of deformation in uniaxial tension was studied from 20 to 150° C (rate of temperature increase 1.5° C/min) as a function of the nature of the fibers and the binder, their relative proportions, and the density and weight of the material. A theoretical explanation of the observed effects is offered.Mekhanika Polimerov, Vol. 4, No. 2, pp. 300–303, 1968     

Three-dimensionally reinforced woven materials

The article presents experimental data on the deformation and strength characteristics of a number of materials reinforced with three-dimensionally woven multilayer glass fabric, which are compared with the corresponding data for traditional glass-reinforced plastics. The accuracy of the formulas proposed [1] is evaluated. The effect of prestressing the warp and weft fibers on the mechanical properties of the material was investigated. The effectiveness of simultaneous prestressing of the warp and weft was evaluated; the magnitude of the optimal force was established.See [1] for report 1.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 471–476, May–June, 1970.     

The influence of the diameter of the glass fibers on the compressive strengths of glass-fiber-reinforced plastics

The authors investigate the stability of the five-layer model of a reinforced polymer. With the aid of a system of fourth-order differential-difference equations derived from the condition of equilibrium of the elements of the model and the compatibility of deformations at the interface, they derive an equation relating the compressive strength of an oriented glass-fiber-reinforced plastic to the diameter of the reinforcing fibers. They show experimentally that the strength of the glass-fiber-reinforced plastic increases with the fiber diameter; this relation is fairly well approximated by a straight line.All-Union Scientific-Research Institute of Glass-Fiber-Reinforced Plastics and Fiberglass, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 626–630, July–August, 1972.     

Study of the effect of the dressing of carbon fibers on the properties of carbon-fiber-reinforced plastics based on polyacetals

Studies are made of the mechanical and friction engineering properties of a copolymer of trioxane-1,3,5 with dioxolan-1,3 reinforced with dressed carbon fibers based on hydrated cellulose. Polyalkyloxysilanes are used as the finishes. The optimum concentrations of the finishes on the fibrous filler are determined. Relations are obtained to describe the dependence of the mechanical properties of carbon-fiber-reinforced plastics on the type of finish and its effect on the condition of the phase boundary between filler and the polymer matrix. The effect of adhesion of the polymer to the fibrous filler on the properties of a randomly reinforced thermoplastic composite is also determined. The dependences of the friction engineering properties of polyacetal-based carbon-plastics on the loading parameters of the friction-loading unit are examined. The material that is developed has high values of strength, elastic modulus, and notch toughness and low values of the friction coefficient and shrinkage. The material can be used as structural and anti-friction elements in rocketry, aviation, and the automobile industry.Ukrainian State Chemical Engineering University, Dnepropetrovsk. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 90–97, January–February, 1997.     

Deformation and strength of hybrid composites reinforced with unidirectional fibers. 1. Numerical models

The hybrid composite consists of n(n > 2) jointly working phases. We define the thermomechanical characteristics and strength of composites by filling and reinforcing materials thermomechanical characteristics and strength basing on the suggestion that thin and strong fibre reinforced composite is quasiuniform, and there is a continuous contact between the filling medium and reinforcing fibers. The development of a mathematical model of the design under consideration has been based on following assumptions: 1) for irreversible processes, the classical thermodynamic postulates are valid, and they are introduced as functions of state of internal energy and entropy; 2) for a solitary volume of materials, internal energy is assumed to be proportional to the volume fraction of the j-th phase v_j; 3) for the material pressure limit conditions just before the essential damage, it is suggested that: a) the whole composite as well as the components are steady, i.e. Drukker's postulate is valid; b) the deformation law associated with the corresponding strength surface is valid, and c) small values of increases in plastic deformation play the leading role. The strength of unidirectionally reinforced hybrid monolayers is predicted by using a linear programming code.Presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October, 1995).Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 2, pp. 186–192, March–April, 1995.The studies were carried out with financial support of the International Scientific Fund founded by G. Soros.     

Electro- and magnetostatics of reinforced polymers

On the basis of previously proposed models of reinforced media with regular structure, a method is developed for determining the electromagnetic fieldand dielectric and magnetic constants of reinforced polymers treated as ideal dielectrics. The solution obtained describes the static electromagnetic field and is suitable for investigating the propagation in reinforced media of electromagnetic waves whose length exceeds the distance between adjacent fibers. The dependence of the macroscopic constants on the orientation and volume content of the reinforcement is investigated.Institute of Mechanics, AS UkrSSR, Kiev. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1130–1133, November–December, 1968.     

Elasticity of the crystal lattice of polyethylene terephthalate

The elasticity of the crystal lattice of polyethylene terephthalate was studied along and across the axes of the polymer molecules. The elastic modulus across the chains depended on the degree of crystallinity and the interplane distances in the directions of thea and b parameters of the unit cell. The nature of the elastic deformation in the crystal lattice was analyzed, and its elastic modulus along and across the axes of the chains was calculated. On loading biaxially oriented amorphous-crystalline polymers with a tensile stress applied in the direction of one of the orientation axes of the polymer, the stresses in the crystallites oriented along and across the external applied force and the amorphous regions in series with them were equal to the stress in the sample averaged over the cross section.Deceased.Translated from Mekhanika Polimerov, No. 6, pp. 982–986, November–December, 1972.     

Effect of gamma radiation on the cracking and mechanical properties of Kapron (polycaprolactam)

The results of a mechano-optical investigation of irradiated oriented polycaprolactam film are discussed. After irradiation comparatively large cracks running at right angles to the orientation axis appear in the film; these are responsible for the reduced tensile strength and deformability of the polymer.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad; Lenin Tadzhik State University, Dushanbe. Translated from Mekhanika Polimerov, No. 4, pp. 756–758, July–August, 1971.     

Polypropylene reinforced with aramid and glass fibers

The effect of the chemical nature of the aramid fibers Phenylone, Terlon, Armos, and SVM on the mechanical, thermophysical, and antifriction properties of reinforced polypropylene was investigated. It was found that the composite filled with SVM fibers based on a stiff-chain polymer has high tensile strength and bending modulus. Reinforcement of polypropylene with Phenylone stiff-chain fibers produces a composite with a high impact viscosity. Organoplastics based on polypropylene and aramid fibers have a low density and friction coefficient and high durability. Reinforcement of polypropylene with aramid (SVM) and glass fibers increases the technological properties of the composites. The glass-filled organoplastics developed can be used in instrument making, radio engineering, and machine building as antifriction and construction materials.Ukrainian State Chemical Technological University, Dnepropetrovsk, Ukraine. Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 106–110, January–February, 1996.     

Theoretical and maximum attainable strength of various uniaxially oriented polymers (film,fibers)

The theoretical strength of various ideally oriented synthetic fibers was calculated. The calculation was based on an assumption that the rupture of polymers involves simultaneous breaking of molecular chains and pulling asunder the chain ends. The temperature-time dependence of the strength of fibers was analyzed and the maximum attainable strength of fibers of various kinds was calculated to show that it is 2–5 times higher than that recorded in practice. The main causes of the difference between the attainable and attained levels of strength are associated with imperfections of the supermolecular structure and an insufficient degree of orientation of materials of this kind. The principal means of obtaining high strength levels of synthetic fibers were discussed.Mekhanika Polimerov, Vol. 2, no. 6, pp. 845–856, 1966     

Self-reinforcement of liquid-crystal polymers at static and dynamic loading

The self-reinforcement effect of a solid uniaxially oriented SVM-K liquid-crystal polyamide and a copolyester of hydroxybenzoic and hydroxynaphthoic acids has been investigated by tensile-strength, stress-relaxation, and dynamic methods. The samples were prepared by spinning from lyotropic solution (SVM-K) and from a thermotropic melt (polyester). The tensile-strength and stress-relaxation tests were performed on complex fibers and the dynamic test on single fibers. The set of stress-strain curves, changing from a convex shape with two linear sections (at room temperature) to a concave shape (at high temperatures) is shown for both materials in Fig. 1. There is a pronounced difference between the deformation mechanisms at low and high strains in the stability of rigidity. At high temperatures the rigidity becomes less than the initial one during deformation and the current modulus at high strains has the same value within large ranges of temperatures and strains (Fig. 2). A low-deformation transition of another physical parameter than the yield-stress has been found. The stress-strain diagram for both investigated polymers has been generalized by using the constant value of the current modulus for the normalization of the stress value (Fig. 3). The stress-relaxation phenomena are shown to be anomalous. At high temperatures the stress-relaxation intensity decreases with increasing deformation, i.e., after deformation the polymer is characterized by a stability of rigidity which is higher than the initial value (Fig. 4). The dynamic modulus appears to increase with increasing deformation rate (Fig. 5). Due to these peculiarities the liquid-crystal polymers must be considered not only as normal high-modulus reinforcements for composite materials but also as materials, self-reinforcing under loading.Translated from Mekhanika Kompozitnykh Materialov, Vol. 30, No. 4, pp. 435–441, July–August, 1994.