Strength and deformation properties of fiberglass-plastic in the flat stressed state as a function of reinforcement structure

Conclusion Limiting strength values have been ascertained in the flat stressed state as a function of reinforcement structure. The change in each strength surface tensor component as a function of reinforcement intensity has been approximated by the piecewise-linear approximation method. A strength condition has been derived which can be used in optimization problems. The problem of the optimum reinforcement structure of a composite at various ratios of the stresses ₁₁, ₂₂, and ₁₂ has been examined. By using the strength condition, one can predict strength values for structures which appear in the class of materials in question with various reinforcement intensities. The procedure developed can be used in designing composite materials.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 848–859, September–October, 1978.     

Possibilities of a nondestructive one-parameter method of checking the strength of anisotropic glass-reinforced plastics in uniaxial compression

A nondestructive method of checking the strength of glass-reinforced plastics (GRP) in finished products is proposed. This method is based on the correlation, investigated by the authors, between the modulus of elasticity and the compressive strength determined by a standard method. Various orientations in the plane of reinforcement of glass-reinforced plastics with different ratios of the orthogonally arranged fibers are investigated. It is proposed to determine the modulus of elasticity from the propagation velocity of an ultrasonic pulse measured under conditions of one-sided access to the surface of the product."Ritm" Research-Production Association, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 909–919, September–October, 1974.     

Structural susceptibility of strength characteristics of polystyrene under uniaxial stretching

The structural susceptibility of the strength characteristics of polystyrene under uniaxial stretching and under test conditions with = const and v_elong = const was studied at 20–100°C. The low structural susceptibility of the durability and durability-equation parameters is due to a change in the elementary fracture volume at different test conditions. It was proposed to characterize the degree of participation of chemical and intermolecular forces by the value U₀/.Moscow Technological Institute of Meat and Milk Industry. Translated from Mekhanika Polimerov, No. 6, pp. 979–984, November–December, 1974.     

Effect of fillers on the hardness and structural order of polymers

The effect of various finely dispersed filler particles differing in size, structure, and the chemical nature of the surface, on the hardness of one crystalline (polycaproamide) and two amorphous (polystyrene and polymethylmethacrylate) polymers has been experimentally investigated. The observed changes in hardness are related with a change in the structural order of the polymer under the influence of the filler and with the formation of structures of different strength by the fillers in the polymer.Kiev Shevchenko State University. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1077–1081, November–December, 1968.     

Optimal designing of orthotropic cylindrical shells fastened to elastic filler

Conclusions A method has been proposed for optimally designing an orthotropic cylindrical shell rigidly fastened to an elastic and isotropic filler of finite dimensions. The design takes into account simultaneous action of pressure, body forces, and heat on the structure. The optimum design has been calculated for the case of temperature-dependent elastic properties and strength characteristics of the tape. The method allows also for limitation on the strength of the filler. The convergence of the iteration process schematically shown in Fig. 2 is quite fast. Indeed, for the given design variant, the condition of manufacturability (1) is satisfied with a sixfold margin in the third approximation (n=3) already.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 91–94, January–February, 1984.     

Friction of polymeric materials

The case of contact of polymer and metallic surface has been examined. A formula is proposed for calculating the contact area as a function of time of holding the compression surface under load and for calculating the coefficient of friction, the dependence of Young's modulus and shear strength on temperature, deformation rate, and average force on the contact surface being taken into account. The nature of deformation of irregularities on the surfaces of polymeric materials under the action of normal and tangential loading has been examined.See [1] for Communication 1.Institute for Polymer Mechanics, Academy of Sciences of the Latvian SSSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 809–815, September–October, 1972.     

Effect of thermal treatment temperature on the structure and properties of carbon fibers

Conclusions 1. It has been shown that the presence of a maximum in the dependence of strength on Young's modulus for carbon fibers made from PAN fiber may be explained by an effect of the process of temperature stress accumulation which takes place under the conditions of isometric heating. The start of this process, which causes a rearrangement of the internal structure of the high-modulus fiber, coincides with the start of the anomalous rise in fiber density.2. The interconnection between surface and internal defects and the elastic-strength properties of carbon fibers made in the temperature treatment range 600–3000°C has been studied.3. Original data on the elastic-strength properties of borided carbon fibers have been obtained; the structure of these is marked by a high degree of perfection. It has been shown that in boriding, which facilitates graphitization of the carbon, the process of regular reduction in fiber strength which is reached in the precrystallization stage is somewhat retarded.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1036–1042, November–December, 1976.     

Nonlinear equations of a timoshenko-type theory of laminated anisotropic shells

In recent years analysis of the stress—strain state of shell structures made out of composite materials has been based on refined shell theories which take into account strains in the direction normal to the reference surface. There are several approaches to the formulation of the refined theories. One can point to shell theories developed on the basis of variational principles (e.g., [1, 2]) as well as theories created with the help of iterational processes (e.g., [3–6]). A resolving system of nonlinear equations for laminated anisotropic shells has been derived in the proposed research based on the Reissner variational principle [7, 8]. A similar linear theory which takes into account the strain e₃₃ also has been developed in [1]. If the shear stiffnesses of the layers differ greatly from each other in the transverse direction, then one can treat the shell structure as a single-layer shell of nonuniform structure. In this case it is advisable to solve a problem of the type of a uniform shell with minimal stiffnesses.Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 501–507, May–June, 1979.     

Effect of the geometry of the structure on the strength distribution of multilaminate tridirectional reinforced plastics

Conclusion The proposed analytical method makes it possible to predict the strength distribution of an LRP of the type [0/±]_s from its structure (the geometry of the packet, the number of layers, and the strength properties of the layers) in a plane stress state. Allowance is made for the random character of the strength properties of the layers, which makes it possible to evaluate the reliability of the LRP for both determinate and random loading. A criterion was formulated for the optimum design of the structure of an LRP with respect to ensuring maximum reliability for specific loading conditions. We also evaluated the effect of the parameters of the structure and the characteristics of the plane stress state on reliability. According to the results of a numerical analysis performed with the above-developed structural model of the failure of an LRP — with allowance for the random character of the strength properties of the layers — the imbalance of the laminated packet which occurs during failure can be ignored. The method used to predict the strength distribution of the LRP, involving determination of the strength distribution law of an RSE and subsequent examination of the loading of parallel-connected RSEs, is promising for other reinforcement schemes as well.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 805–812, September–October, 1988.     

Estimating the impact strength of plastics

A method of estimating the impact strength of plastics in transverse two-support bending is proposed. It is shown that if specimens of different size are tested under certain conditions, the ratio of the work done in breaking the specimen to the volume of the specimen between the supports will be the same.Novosibirsk Kuibyshev Structural Engineering Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1109–1112, November–December, 1971.     

Low-cycle fatigue of a composite substance containing a dispersed filler in cyclic compression

Conclusions 1. The lifetime of a composite material having a dispersed filler has been examined under conditions of low-cycle compression.2. It has been shown that, in distinction from materials of fibrous structure, the lifetime of this material is determined, not by a breakdown in the continuity of structure, but the deformability of the polymer matrix.3. The absence of a correlation between the static and fatigue strengths of composite mateials from cold and hot curing is caused by the different effect of the structure of the cured binder as a component of the material on the ultimate static characteristics and creep, whose relaxation character is more clearly expressed.4. Creep of the binder and the strength of the microspheres are the main factors which determine the lifetime of the material in question in cyclic compression.All-Union Scientific-Research Institute of Synthetic Resins, Vladimir. Translated from Mekhanika Polimerov, No. 4, pp. 653–657, July–August, 1978.     

Strength of rigid oriented amorphous polymers

A method is proposed for obtaining uniaxially oriented specimens of amorphous unfractionated polymer with a particular oriented chain length. The length of the oriented chains and their molecular weight M_c depend importantly on the conditions under which the polymer is stretched. It is shown that the strength of specimens obtained by stretching at constant M_c increases linearly with the relative fraction of oriented phase. The slope of this linear relation increases with the length of the oriented molecular chains. The ratio of the maximum strength of fully oriented polystyrene to the strength of the unoriented material is found to be 78 instead of the value of 6 given in [6].Mekhanika Polimerov, Vol. 3, No. 6, pp. 1048–1053, 1967     

Comparative performance of living and dead bony tissue under static and dynamic loading

The dependence of the mechanical properties of bony tissue on different conditions of storing the samples has been studied. As the performance characteristic under static loading we used the ultimate compressive strength of the bony tissue, and under dynamic loading we used the specific impact strength.Paper presented at the First All-Union Conference on Engineering and Medical Biomechanics, Riga, October, 1975.I. M. Sechenov First Moscow Medical Institute. Translated from Mekhanika Polimerov, No. 4, pp. 647–649, July–August, 1975.     

Effect of gamma radiation on the mechanical properties of polyvinylidene fluoride

The variation of the strength and relative elongation at break with radiation dose has been investigated for unoriented block specimens of PVF₂ and for oriented specimens with different crystalline structure ( and ). A certain difference is observed in the behavior of the irradiated oriented specimens and an important difference in the behavior of oriented and unoriented specimens of PVF₂ with the same crystalline structure (). On the basis of the data obtained and the results of a study of the crystalline and supermolecular structure of the irradiated PVF₂ specimens it is concluded that there is a difference in the state of the amorphous regions in the oriented and unoriented PVF₂.Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 146–149, January–February, 1973.     

Rational structures for spherofibrous composites. 2. 4Dm models

A method of calculating elastic moduli from component properties is proposed for a 4D composite. It is established that when subject to shear, composites with such a structure cannot be described by Hooke's law for anisotropic bodies. It has been found that 4D₀ and 0m composites with a fixed bulk content of components possess nearly equivalent normal-elasticity indicators. The latter makes it possible to use these less expensive materials.See [1] for report 1.A. A. Blagonravov Machine Science Institute, Russian Academy of Sciences, Moscow, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 3, pp. 370–376, May–June, 1997.     

Analysis of the zonal winding pattern of thin spherical shells

Conclusions 1. A method has been proposed for calculating the zonal pattern of winding thin spherical shells.2. The tested strength of shells wound by the calculated pattern correlates with the theoretical.3. The proposed calculation apparatus makes it possible to calculate winding patterns with any variants of angles and number of zones.4. A zonal pattern in a spherical shell having a connecting pipe of small diameter can give a mean constructional strength which does not exceed 0.39 times the strength of the unidirectional plastic (as against 0.5 in the ideal case for a sphere of bidirectional material), i.e., not more than 78% of the strength of the plastic is realized.5. The bearing ability of a sphere wound by the zonal method is 22% less than that of a long cylinder (with no bottom) made by the same winding method.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 625–631, July–August, 1978.     

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.     

Temperature dependence of the strength of a woven composite in a plane state of stress

Conclusions On the basis of an analysis of test results obtained by typical patterns of simple momentary quasistatic loading at various temperatures within the 20–150°C range, we have found a family of strength surfaces for a woven organic plastic material in a plane state of stress in the reinforcement plane. These experimentally found strength surfaces can be approximated by the equation of a second-degree surface. It has been established that the range of safe states of stress in the stress space narrows nonuniformly with rising temperature; namely, this narrowing is accompanied by a shift of the center and a reorientation of the axes of the strength ellipsoid. We have revealed and described the temperature dependence of the components of the strength surface tensors involved in the strength criterion. The data can be used for predicting the strength of a composite material under consideration when the latter is subject to simple quasistatic loading patterns in the three-dimensional (₁₁, ₂₂, ₁₂) stress space in the reinforcement plane within a given test range of temperatures.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 452–457, May–June, 1978.     

Effect of temperature and strain rate on the adhesion of polyvinyl butyral to glass

The shear strength of silicate glass bonded with polyvinyl butyral has been investigated over a broad temperature interval together with the effect of plasticization of the polymer on the strength of the bond. The _adh ^–t curves have intervals corresponding to adhesion failure, cohesion failure of the substrate, and cohesion failure of the adhesive, respectively. The dependence of adhesion on strain rate has been investigated and a maximum observed at 20 mm/min.Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1104–1107, November–December, 1970.     

Effect of the sign of the shear stresses on the shear strength of reinforced plastics

The effect of the sign of the shear stresses on the shear strength has been investigated for a glass-reinforced plastic of the SVAM type with various ratios of the longitudinal and transverse reinforcement in shear in the plane of reinforcement in axes turned through 45° relative to the direction of reinforcement. More than 80 tubularspecimens were tested. The shear strengths T ₄₅ ⁺ and T ₄₅ ^– corresponding to shear stresses of different signs can be found from uniaxial tests in tension and compression in the direction of the reinforcement.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 2, pp. 262–268, March–April, 1971.