Stability loss of reinforced cylindrical shells under isotropic external pressure

Conclusions 1. Upon the loading of a composite shell having a metallic matrix the shear effects are insignificant even in the case of comparatively large volume reinforcement contents and wall thicknesses.2. The principal modulus of a material which determines the stability of a reinforced shell upon isotropic external pressure is the secant modulus in the circumferential direction.3. In the case of complex reinforcement schemes some decrease in the stability of the shell is possible, probably due to an imperfection in reinforcement technology.Institute of Solid State Physics, Academy of Sciences of the USSR, Moscow Region. Translated from Mekhanika Polimerov, No. 1, pp. 90–95, January–February, 1977.     

Load-bearing capacity of compressible plates of glass-fiber-reinforced plastic with different placement of the reinforcement

The effect of placement of reinforcement on the load-bearing capacity of circular and rectangular plates compressible in the reinforcement plane was evaluated experimentally. Four placement schemes for circular plates and nine for rectangular plates were investigated. Different schemes of supporting the edges were studied. Two mechanisms of exhaustion of the bearing capacity were revealed. A numerical evaluation and comparison of different placement schemes with respect to the value of the critical and breaking load are given. The role of the actual realization of clamping and nonlinearity of the material is shown. A comparison with analytic relations taking into account the characteristics of the material is given.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 646–653, July–August, 1972.     

Evaluating the effect of whiskerization of the fibers of composites on the fundamental frequency of a laminated cylindrical shell

Conclusion The calculations showed that whiskerization of the reinforcement of the structural material of multilaminate shells makes it possible in some cases to increase the fundamental vibration frequency of the structure up to 15–20%. In combination with the well-known [1] effect of improved strength characteristics for a whiskerized composite in the transverse and shear directions, this finding allows us to conclude that whiskerized structural materials are more efficient than ordinary laminated composites in shell-type load-bearing structures. Here, the greatest benefit can be expected in the case of whiskers which have higher elastic moduli than the main reinforcement. Since considerably higher reinforcement intensities can be achieved in whiskerized laminated composites than in composites with a reinforcement characterized by an arbitrary three-dimensional structure, it can be concluded on the basis of the results obtained here that, at least for shells of moderate thickness (10 < R/h 50), whiskerized composites are the optimum structural material for load-bearing shells.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 1022–1027, November–December, 1987.     

Elastic characteristics of ferrocement reinforced with woven meshes

Applying structural mechanics methods for composite materials, we have worked out a procedure for predicting the elasticity modulus, the shear modulus, and Poisson's ratio for ferrocement taking into account the elastic properties of the components, the wire diameter, the mesh size, and the distance between the meshes. The results make it possible to exploit the potential of such reinforcement to the fullest.Translated from Mekhanika Kompozitnykh Materialov, Vol. 30, No. 4, pp. 526–530, July–August, 1994.     

Dependence of elastic and strength characteristics of high-modulus composites on schemes of reinforcement

The elastic and strength characteristics of high-modulus composites with 12 different reinforcement schemes have been studied thoroughly. The effect of reinforcement schemes on change in elastic and strength characteristics of composites has been evaluated. A calculation of the elastic characteristics of high-modulus composites has been performed from the properties of the reinforcement and binder, and a comparison of the results with experimental data is given. Diagrams of deformation upon extension of the composites studied are given.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1019–1027, November–December, 1974.     

Propagation of elastic waves in certain composites

Conclusions 1. Relationships have been obtained for determining nine elastic characteristics of orthotropic composite materials from the properties of the starting components and the assigned reinforcement scheme.2. Formulas are given for calculating the propagation velocity of three types of elastic flat waves for an arbitrary direction in one of the planes of elastic symmetry of a uniform orthotropic material.3. It has been shown that the velocity of the first arrival of a packet of ultrasonic vibrations which is recorded in an experiment is equal to the velocity of motion of the wave front in a limitless medium even for rather thin (5–10 mm) fiberglass-plastic specimens with unidirectional or cross-reinforced schemes.4. The dependences of elastic properties and rates of propagation of elastic vibrations on direction which are calculated theoretically from the properties of the starting components and the reinforcement scheme agree satisfactorily with experimental results.Translated from Mekhanika Polimerov, No. 3, pp. 531–536, May–June, 1978.     

Application of the finite-element method to improve the quasi-exact reinforcement theory of fibrous polymeric composites

In the paper, the WL quasi-exact reinforcement theory of fibrous polymeric composites is improved. An optimum compatibility condition related to the transverse shear problem for a unit cell, which brings solutions closest to reality, is derived. This condition is formulated in the form of a linear combination of maximum radial and circumferential displacements. Optimum coefficients of this combination are determined by comparing analytical and numerical solutions for a test specimen in the form of a rectangular thin plate, which is in a plane strain state and is subject to selected loading schemes. The analytic solutions are obtained for a homogenized material by using the WL reinforcement theory. The numerical solutions are found for an actual heterogeneous composite material by using the finite-element method, and they verify the WL reinforcement theory, in particular, the admissibility of Hills assumption. An analysis performed for two composite materials shows that the improved WL reinforcement theory gives adequate displacement fields.Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 1, pp. 79–92, January–Febrauary, 2005.     

Effect of cellular structure on the mechanical properties of plastic foams

A generalized equation for the compressive stress-strain diagrams of plastic foams is derived on the basis of a 14-faced model of the cell. The results obtained make it possible to predict the polymer base and type of cellular structure required to obtain a foam with predetermined mechanical properties in compression. The calculated values are shown to be in satisfactory agreement with the experimental data.Vladimir Scientific-Research Institute of Synthetic Resins. Translated from Mekhanika Polimerov, No. 4, pp. 594–602, July–August, 1970.     

Experimental evaluation of the strength anisotropy of a unidirectionally reinforced organic fiber-reinforced plastic

Conclusions The strength of a unidirectional organic fiber-reinforced plastic has been experimentally determined in various special cases of plane stress. An analysis of the data obtained shows that it is possible to describe the strength of the material in plane stress by means of a second-order surface equation containing linear and quadratic terms. The dependence of the strength in tension and compression on the angle between the directions of loading and reinforcement has been predicted and experimentally confirmed using the values found for the components of the strength surface tensors. The results of the study can be used to estimate the strength of multilayer organic fiber-reinforced plastics in cases where a unidirectionally reinforced layer can be taken as the basic structural element of the material.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 799–803, September–October, 1979.     

Mechanical properties of a composite with a carbonized matrix

The effect of reinforcement schemes that differ in the magnitude of the disorientation angle of neighboring filler layers on the mechanical properties of a "carbon-carbon" composite under extension, compression, or bending is shown.Translated from Mekhanika Polimerov, No. 2, pp. 235–240, March–April, 1976.     

Relation between the parameters of bond rupture kinetics and the lifetime of polymeric materials

The dependence of the lifetime of a polymeric material on the level of the applied stress and its duration of action is established on the basis of the equation of a first-order thermal degradation reaction. The relations obtained also make it possible to describe the thermal aging process.Second Pirogov Moscow State Medical Institute. Translated from Mekhanika Polimerov, No. 4, pp. 668–675, July–August, 1970.     

Structural theory of the tensile and compressive strengths of reinforced plastics

The strength conditions of unidirectionally and orthogonally reinforced plastics subjected to uniaxial tension and compression in the direction of, and at an angle to, the reinforcement are developed, with consideration given to possible failure of the fibers, binder, or the bond between the fibers and binder. Proposed strength conditions take into account the structure of the material, the properties of its components, and stress concentration.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 988–995, November–December, 1975.     

Statistical analysis of the bearing capacity of rim-spoke flywheels made of reinforced plastics

Conclusion The suggested numerical method makes it possible to plot the distribution functions of the bearing capacity of RSF at the structural level of their design elements (rim, spokes) with a view to the scatter of the strength and strain properties of the used materials and the geometry of arrangement of the structure. This involves taking into account the random nature of the radial distribution in the rim material of both strain and strength properties, which makes it possible to investigate more fully the processes of failure really occurring in RSF. The suggested method is the basis for stipulating a scientifically substantiated safety factor (the theoretical bearing capacity) in dependence on the required reliability; this makes it possible to use a differentiated approach to problems of devising RSF for actual purposes. Our investigations may serve as the basis for solving problems of optimal planning of RSF according to the conditions of the required reliability.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 1041–1047, November–December, 1987.     

Determination of rational structure for spherofibrous plastics

A complete set of elastic constants for various structures of triorthogonally reinforced plastics with a matrix dispersely reinforced by spherical particles has been determined on the basis of the proposed algorithm. Approximate equations are obtained for determination of all integral parameters from data on the components and structure geometry. It is established that for the reinforcement schemes investigated, the shear moduli of the composites have the lowest possible values and are calculated with a higher accuracy than the other elastic constants.A. A. Blagonravov Institute of Machine Science, Russian Academy of Sciences. Moscow, Russian. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 2, pp. 155–160, March–April, 1997.     

Experimental study of thermal expansion of layered carbon-reinforced plastics

Conclusion The nonlinear dependence of the thermal deformations on the temperature for a wide class of layered carbon-reinforced plastics was experimentally demonstrated and the use of the thermal expansion function of the material instead of the corresponding characteristic: the thermal expansion coefficient, was substantiated in the present study. A method for determining the parameters of the thermal expansion functions was developed in consideration of their nonlinear dependence on the temperature and the numerical values were reported for layered carbon-reinforced plastics of two types with typical reinforcement schemes. In addition, the significant dependence of the thermal expansion functions on the geometry of the structure of the carbon-reinforced plastics was observed, and the major possibility of optimum planning of the structure of the material from considerations of geometric stability was demonstrated. The study of thermal deformations of reinforced plastics in consideration of their random character is promising as a result of the significant variance of the experimental data.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 32–36, January–February, 1990.     

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.     

Mathematical modeling of processes of devising fibrous composite materials and thin-walled structural elements by forced winding

Conclusions With the aid of the method of averaging processes in regular media, on the assumption that the temperature field in the semiproduct of PM is homogeneous at all stages of the production of thin-walled articles of CM, we suggested averaged equations of equilibrium, and also constructive algorithms for calculating the effective moduli and defining relations of the material of the semiproduct of CM. On the basis of these equations and the boundary conditions corresponding to them, we showed that it is possible to determine the RTS in a finished product of CM, and also to predict the change of its shape after removal from the mandrel and cutting it up into separate elements. To determine the above-mentioned technological characteristics of thin-walled elements made of fibrous CM, it is necessary to know the physicomechanical characteristics of the fibers and of the PM before and after polymerization; the volume fraction of the reinforcing filler and of the PM during winding, and also the orientation of the reinforcement; the relative change of volume of the PM after heat treatment and cooling; the prestresses in the fibers in the process of winding. It should be noted that the obtained averaged equations make it possible to calculate only the components of the averaged RTS in products of CM. To determine the local stresses in PM and fibers at all stages of making the product, it would be necessary to investigate in detail the rheology of PM at different temperatures.Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 513–527, May–June, 1990.     

Modern trends in the development of fibrous composites

The two main trends in the development of high-modulus composites are considered. Improved methods of calculation sensitive to the effects associated with the weak shear and transverse characteristics are reviewed. It is shown that the disadvantages of composites with a traditional arrangement of the reinforcement can be overcome. The properties of boron- and carbon-reinforced plastics with a traditional reinforcement structure are described and compared with those of three-dimensionally structured materials with two- or three-strand reinforcing. Whiskerized fiber reinforcement is also considered. A program of further research on high-modulus composites is outlined.Presented at the 2nd All-Union Conference on Polymer Mechanics, Riga, November 10–12, 1971.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 541–552, May–June, 1972.     

Effect of heat treatment on the distribution of residual stresses and the properties of epoxy polymers

Conclusions The analysis of the experimental data showed that heat treatment results in a reduction in the stressed state of a polymer, which affects the tensile strength of the material to a greater degree than the compressive strength. During heat treatment, significant changes take place in sections of the polymer damaged by the effect of residual compressive stresses and sections in which the residual stresses change sign. The quantitative relations in the change in the tensile strength of the material in these two sections make it possible to explain the mechanism of the effect of heat treatment and to predict its character.Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 787–790, September–October, 1986.     

A study of the special features of stress relaxation in irradiated polytetrafluoroethylene

As a result of experimental studies of stress relaxation in polytetrafluoroethylene irradiated with various doses (from 2×10⁴ to 1×10⁶ rads), data have been obtained which make it possible to judge the rate of occurrence of relaxation processes in the polymer. A number of special features have been revealed which distinguish the character of occurrence of relaxation processes in the irradiated and nonirradiated material.Plastics Scientific-Research Institute, Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 148–150, January–February, 1972.