Statistical estimate of a static strength criterion for AG-4s two-way glass-reinforced plastic

The statistical characteristics of the static strength of AG-4s entering into the equations of the strength criteria for anisotropic materials are determined. The agreement between a series of existing criteria and the test data is estimated. A theoretical estimate of the mathematical expectation and variance of the function for the criterion best adapted to the material in question is obtained on the basis of the method of linearization of a function of several random arguments. The theoretical and experimental data are compared.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1117–1120, November–December, 1973.     

Concerning the glass fiber strength distribution function

The statistical strength distribution functions of glass monofilaments of various composition are considered. On the basis of the experimental data it is shown that the fiber strength distributions can be described by a three-parameter function of the Weibull type.All-Union Scientific-Research Institute of Glass-Reinforced Plastics and Glass Fibers, Moscow Regions. Translated from Mekhanika Polimerov, No. 1, pp. 131–136, January–February, 1970.     

General criteria of the strength of isotropic media

The limit surfaces of isotropic materials are considered in the invariant spaces of the stress tensor. The general requirements that must be met by limit surfaces are formulated. A three-invariant strength criterion for isotropic media sensitive and insensitive to hydrostatic pressure is given in general form. The convenience of analyzing strength criteria in the two-dimensional space of the base invariants of the stress tensor is demonstrated.Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 251–261, March–April, 1971.     

A study of the physicomechanical properties of carbon fibers at high temperatures

Conclusions 1. Carbon fibers, similar to graphite materials, are heat-resistant and do not Iose their short-term tensile strength in the temperature range studied — 20 to 2000°C.2. Young's modulus of carbon fibers hardly changes in the temperature range 20 to 1200°C, but a significant decrease is observed upon a further increase in temperature.Translated from Mekhanika Polimerov, No. 4, pp. 626–630, July–August, 1977.     

Experimental investigation of the impact strength of Caprolon in linear and plane stress

An apparatus for investigating the impact strength of materials in plane stress is described. The results of testing Caprolon in plane stress and linear tension over a broad range of strain rates are presented.Leningrad Kalinin Polytechnic Institute. Translated from Mekhanika Polimerov, No. 2, pp. 332–334, March–April, 1971.     

Long-time strength of isotropic polymers in plane stress state

A criterion of strength of isotropic polymers in the form of the critical work done by stress was postulated and shown, by statistical analysis, to be independent of the time and form of loading. The introduction of the time factor in the existing theories of strength of isotropic materials was postulated and experimentally verified with the aid of this criterion.Mekhanika Polimerov, Vol. 2, No. 6, pp. 837–844, 1966     

Strength of honeycomb plastics in a flat stressed state

The strength of textile and paper honeycomb plastics in the flat stressed state is discussed, under the simultaneous action of compressing and shearing stresses. The application of a generalized strength criterion for anisotropic materials to honeycomb plastics is investigated.V. A. Kucherenko Central Scientific-Research Institute of Building Constructions, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 936–938, September–October, 1972.     

Statistical theory of defect buildup in composite materials and the scale-factor effect in reliability

A statistical theory of fracture based on the concept of defect buildup is applied to composite materials with a definite fiber orientation. On the premise that the concentration of defects that precede a fracture is sufficiently low, asymptotic distributions of defectiveness are established and asymptotic expressions for the reliability function are derived. It appears feasible to use this theory for predicting the reliability and the scale-factor effect for structures made of oriented composite materials.Moscow Power Institute. Translated from Mekhanika Polimerov, No. 2, pp. 247–255, March–April, 1976.     

Change of strength of polymeric materials in the process of orientation

In the process of orientation the strength of polymeric materials changes as a result of a net increase in the number of ordered structural elements. It is shown that the model obtained can be used to predict the effect of orientation on the strength of polymers. The theoretical relations satisfactorily describe the available experimental data.Scientific-Research Institute of the Tire Industry, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 848–853, September–October, 1970.     

Dynamic compressive strength of epoxy composites

The strength of laminated and unidirectionally reinforced composite materials was investigated in conditions of dynamic uniaxial compression with a strain rate of 50–1000 sec^–1 using the split Hopkinson pressure bar method. It was shown that in conditions of dynamic compression, glass/epoxy, aramid/epoxy, and carbon/epoxy composites exhibit elastic-brittle behavior with anisotropy of the strength and elastic properties. The effect of the strain rate on the strength characteristics of fiberglass-reinforced plastics was demonstrated.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 6, pp. 776–782, November–December, 1995.Presented at the Ninth International Conference on the Mechanics of Composite Materials (Riga, October, 1995).     

Distribution of shearing stresses under three-point flexure in beams made of composite materials

Conclusions 1. When short beams made of composite materials with span-to-height ratios within the 4.0–5.0 range are tested in three-point flexure, the profile of shearing stresses over the height of a beam cross section departs appreciably from a parabolic one over approximately 40% of the span length.2. The zones of a perturbed state of stress, which appear in short beams tested in three-point flexure, render this method unusable for determining the interlayer shear strength of composite materials on "ultrashort" specimens.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 56–62, January–February, 1977.     

Technological anisotropy of chaotically reinforced glass-fiber-resin materials

The authors investigate the strength properties of chaotically reinforced glass-fiber-resin materials in compression-molded and injection-molded artifacts of complex shape and also the density, water absorption, and binder content in various zones in the artifacts. They find anisotropy to be present in the strength indices, owing to orientation of the reinforcing elements during flow of material in the mold. They determine the coefficients of anisotropy of the strength (these are defined as the ratios of the strength in the flow direction to the strength in a perpendicular direction). They suggest a method of estimating the degree of orientation of the reinforcing elements in artifacts made of nonoriented glass-fiber-resin materials.All-Union Scientific-Research Institute of Glass-Fiber-Reinforced Plastics and Glass Fiber, Moscow Region. Translated from Mekhanika Polimerov, Vol. 9, No. 3, pp. 507–515, May–June, 1973.     

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.     

Effect of hydrostatic pressure on the strength properties of polymer materials

On the assumption that the strength characteristics of homogeneous polymer materials depend on the specific volume, equations are derived for the dependence of the strength or high-elastic limit on the hydrostatic component of the stress tensor and temperature. The ultimate strengths in simple tension, compression and shear are considered in relation to brittle and plastic fracture.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 449–454, May–June, 1969.     

Composites reinforced with a system of three straight mutually orthogonal fibers

The effectiveness of reinforcement in direction 3 has been estimated by investigating the mechanical characteristics of two types of three-dimensionally reinforced materials differing with respect to the arrangement of the reinforcement and the fiber content in each direction. The superior transverse stiffness, shear strength, and transverse tensile strength of three-dimensionally reinforced composites based on a system of three mutually orthogonal fibers, as compared with laminated materials, is demonstrated. The theoretical values of the elastic constants, calculated from the relations of [5], are compared with the experimental data.For communication 1 see [5].Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, pp. 1011–1018, November–December, 1973.     

Statistical boundary value problems of polymer mechanics

Research on statistical boundary value problems with applications in the mechanics of reinforced polymers is briefly reviewed. The common features of the models and mathematical methods used in connection with polycrystalline metals and materials of the glass-reinforced plastic type are noted.Sverdlovsk Branch of the V. A. Steklov Mathematical Institute, Academy of Sciences of the USSR. Translated from Mekhanika Polimerov, No. 1, pp. 63–69, January–February, 1969.     

Residual stresses in glass-reinforced plastics parts

The determination of the residual stresses in glass-reinforced plastics elements is considered. It is shown that these stresses reach appreciable values and should be taken into account in strength calculations. Quantitative data are supplied for a series of materials. At normal operating temperatures the residual stresses are stable.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1117–1119, November–December, 1969.     

The scale effect and the statistical theory of strength of polymer coatings

As a result of normal tensile tests on coatings based on ED-6 epoxy resin and kapron applied to a metal surface it has been established that the fracture is brittle in character and accompanied by a scale effect and a regular distribution of the strength values for specimens of the same type. It is shown that the data obtained are all in good agreement with the statistical theory of strength.State All-Union Scientific-Research Technological Institute for the Repair and Maintenance of Tractors and Agricultural Machinery, Moscow. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 839–843, September–October, 1968.     

Technology and Some Mechanical Properties of Biocomposites Based on Mineral Components

Two types of new composite implant materials are investigated. Their mechanical characteristics, biocompatibility, and the dynamics of bond strength between the biocomposites and a live bone tissue are determined. The first type of the biomaterials is based on silicate glass and hydroxyapatite. Both the natural and a synthetic hydroxyapatite were used. The second type of the biomaterials was made of an ultrahigh-molecular polyethylene and the synthetic hydroxyapatite. Composite materials of both the types were implanted in the rabbit femur. The bond strength between the bone tissue and the implants was determined in 2, 4, 10, and 25 weeks.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 273–282, March–April, 2005.     

Investigation of the wedge pressure (Ludwik) method of testing certain plastics

The feasibility of Ludwik's method, which consists in squeezing a test piece between two wedges, as a means of determining the tensile strength of polymeric materials is demonstrated.Riga Polytechnic Institute. Riga Lenin Komsomol Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 2, pp. 366–369, March–April, 1971.