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.     

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.     

Strength properties of unidirectionally reinforced hybrid composites

Conclusions Experiments were carried out with several types of unidirectionally reinforced hybrid composites (organic fiberglass plastic, organic carbon-reinforced plastic, organic boron-reinforced plastic, and carbon fiberglass plastic) with various ratios of the volume content of the fibers in various modes of simple quasistatic loading. It is shown that the strength of the examined materials in the plane stress state can be described phenomenologically by the polynomial criterion of strength with the components of the tensors of the strength surface depending on the structural parameters. The result can be used to predict (carry out interpolation calculations) the strength of the above-mentioned composites within the examined ranges of the volume content of the reinforcing fibers to optimize the selection of the type and ratio of the content of various fibers in the hybrid composite taking into account specific requirements on the strength properties of the material in the structures.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 35–41, January–February, 1984.     

Experimental investigation of the strength of glass-reinforced plastics in biaxial compression in three planes of symmetry

Glass-reinforced plastics (GRP) with fiber (wound) and fabric (hot-molded textolites) reinforcement have been investigated in biaxial compression in the three planes of symmetry. The high strength in biaxial compression in the transverse plane, observed for all the GRP investigated, is explained. A method of investigating the tensile strength of the fiber components of the GRP from the results of testing a unidirectional composite in biaxial compression in the transverse plane is proposed. The possibility of a nondestructive estimation of the strength of GRP in biaxial compression at an arbitrary stress ratio is demonstrated.Translated from Mekhanika Polimerov, No. 1, pp. 63–72, January–February, 1976.     

Tensile testing of high-strength unidirectional composites

Conclusions 1. In order to obtain stable values of the tensile strength of high-strength unidirectional composites it is necessary to use bar specimens with pressboard end reinforcement 90–110 mm in length.2. In determining the strength on specimens without end reinforcement it is necessary to select their size and shape with allowance for the transverse compressive strength, the shear strength and the taper of the grip jaws.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 717–723, July–August, 1978.     

Mechanical properties of glass fabric-reinforced plastics in tension and compression normal to the plane of reinforcement

The behavior of glass-reinforced plastic based on ASTT (b)S₂-O fabric and NPS-609-21M resin in tension and compression normal to the plane of reinforcement has been investigated and the mechanical characteristics determined. Recommended values are given for the size and shape of the test pieces, and a method of determining the tensile and compressive characteristics of glass-reinforced plastics is proposed.Leningrad. Translated from Mekhanika Polimerov, Vol. 4, No. 5, pp. 803–809, September–October, 1968.     

Determination of the reliability of glass structures with steady and alternating loads

A method is developed for determining the reliability (nonfailure probability) of glass structures for a prescribed loading duration by alternating loads; an equation is obtained for calculating the reliability of glass structures from material (glass) strength parameters. It is shown that reliability with steady loads is a particular case of reliability with alternating loads. The method developed is based on a correlation established between long-term strength of the material and glass structure, and use of a new criterion of equal reliabilities for alternating loads.Lvov. Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 21, pp. 90–97, 1990.     

Optimal reinforcement of a material in a known state of stress

The problem of minimizing the total reinforcement of a material in a known state of stress is considered. In the proposed geometric formulation the problem reduces to the determination in normal stress space of the shortest path from a point representing the state of stress to the region of strength. Examples of the determination of the relative area of reinforcement in three-dimensional and plane states of stress are given for characteristic regions of strength: for plane stress and plane strain the calculations lead to expressions that permit the relative areas of reinforcement to be determined directly.Kucherenko Central Scientific-Research Institute of Building Structures, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 922–930, September–October, 1971.     

Variation in angles between fibers in forming articles from unhardened composite materials

Conclusion The Gaussian curvature of the surface and the geodesic curvatures of the reference filaments of the fabric exerts a significant influence on the interfilament angles of the base fabric of composites formed to a surface. It is demonstrated that the lines of constant grid angle in the coordinates of the plane fabric are close to hyperbolas, while the optimum layout of the base fabric of the composite material in the sense of least fiber disorientation is that layout for which the lines of the seams intersect the fibers of the fabric at an angle of 45 °.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 138–142, January–February, 1991.     

Bending of a rectangular orthotropic glass-reinforced plastic plate under a transverse load

The Bubnov-Galerkin method is used to solve the problem of the bending of a clamped flexible orthotropic plate. An equation relating the deflection and the load is obtained. An experiment on a plate made of polyester plastic reinforced with satin-weave glass fabric is described. It is shown that within certain limits the deflections at the center of the plate and the combined stresses along the clamped edges are in good agreement with the theoretical values. The limits of applicability of the first-approximation formulas are investigated.All-Union Scientific-Research Institute of Railroad Transport, Ural Division, Sverlovsk. Translated from Mekhanika Polimerov, No. 4, pp. 674–679, July–August, 1969.     

Theoretical and experimental investigation of anisotropic damage in textile-reinforced composite structures

In the present work, a phenomenological plane-stress damage-mechanics-based model for textile-reinforced composites is presented and its predictive capability is evaluated by carrying out a series of experimental tests. Damage variables are introduced to describe the evolution of the damage state and, as a subsequence, the degradation of material stiffness. For calculating the nonlinear stress and strain distribution of complexly loaded composites with a textile reinforcement, a special emphasis has to be placed on the interaction between the fiber failure due to the stress in the fiber direction and the matrix failure due to the transverse and shear stresses. This demands the formulation of realistic failure criteria taking into account the microstructural material behavior and different fracture modes. The new failure criteria, like the fracture mode concepts, consider these fracture modes, as well as further fracture types, in the reinforcement plane. The failure criteria are based on equations for failure surfaces in the stress space and damage thresholds in determining the stiffness degradation of the composite. The model proposed was used to characterize the strength and the failure behavior of carbon-fiber-reinforced composites. For this purpose, several unidirectional and bidirectional tests were performed to determine the specific properties of the material. The specimens were investigated by using acoustic emission techniques and strain-controlled tension and torsion tests.Russian translated published in Mekhanika Kompozitnykh Materialov, Vol. 40, No. 6, pp. 791–810, November–December, 2004.     

A nonlinear model of a viscoelastic medium with allowance for the nature of the state of stress

A simple model of a nonlinear viscoelastic medium of hereditary type is considered with allowance for the nature of the state of stress. A system of experiments for determining the material functions and constants is described and sufficient conditions for the existence of simple loadings are formulated.Moscow Lomonosov State University. Translated from Mekhanika Polimerov, No. 6, pp. 994–1001, November–December, 1969.     

Creep of polymer materials under periodically varying loads

A method is proposed for constructing the creep curves of a material whose nonlinear memory properties are described by Rozovskii's nonlinear integral equation [2] (with allowance for the stress dependence of the relaxation time) under given periodic loading from known creep curves recorded at constant stress. In deriving the theoretical relation certain simplifying assumptions are made (the creep strain accumulated in 1–2 cycles is small, no vibration [4–6]). An experimental check shows that the proposed method can be used to predict the behavior of a material under periodic loading with an accuracy sufficient for practical purposes.Mekhanika Polimerov, Vol. 2, No. 3, pp. 330–336, 1966     

Short-time strength of reinforced plastics in uniaxial compression

The short-time compressive strength of one-way and two-way reinforced plastics compressed in the direction of the axes of elastic symmetry has been theoretically and experimentally investigated with allowance for the mechanical properties of the components and the orientation of the fracture (shear) plane.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 621–628, July–August, 1969.     

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.     

Strength and deformability of reinforced polymers in tension normal to the fibers

The strength and deformability of reinforced polymers in tension across the fibers is investigated. It is assumed that the polymer deforms as an ideal elastoplastic body. Relations are obtained for the nature of the deformation of the polymer between the fibers and the strength and deformability of the composite with allowance for the structural distribution of the components. Theoretical stress-strain diagrams are presented for composites with different reinforcement densities and resin elasticities. The theoretical values of the strength and deformation of reinforced polymers with the load applied across the fibers are compared with the results of experiments on model specimens of epoxy-Thiokol polymers.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 4, pp. 682–687, July–August, 1970.     

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.     

Creep and long-time strength of unidirectional reinforced plastics in compression

An attempt is made to predict the creep and long-time strength of unidirectional reinforced plastics in compression in the direction of the reinforcement from the properties of the components. The reinforcement is assumed to be elastic, while the resin is described by a Boltzmann-Volterraintegral equation with fractional-exponential Rabotnov kernel. Experimentally obtained creep and long-time strength curves are presented for unidirectional reinforced plastics.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 830–835, September–October, 1970.     

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.     

Multifibre polymer composites: Prediction of deformation and thermophysical properties

Conclusions A theoretical and experimental investigation was carried out to examine the possibilities of a structural approach for prediction of elastic constants, creep functions and thermophysical characteristics of hybrid polymer composites reinforced with anisotropic fibres of several types. The theoretical solutions were obtained by generalizing the self-consistent method for the case of a three phase model. The effects of brittle fibre breakdown under tension in the direction of reinforcement of a unidirectional hybrid composite were studied under conditions of a short-term loading and a long-term creep. It has been shown that a creep of viscoelastic fibres plays a principal role in creep of the hybrid composite. It is just this creep that significantly increases the fibre damage during creep of the composite.A variant of the solution has been proposed for predicting the thermorheologically complex behavior of hybrid composites containing not only elastic but also viscoelastic thermorheologically simple components with different temperature-time shift factors. The peculiarities of thermal expansion of hybrid composites and the possibilities for a purposeful control of thermal expansion coefficients by hybridization were studied. The considered thermal interval included a region of transition of the polymer matrix from a glass state into a viscoelastic one.The control tests were performed for specimens of organic/glass, organic/carbon, glass/carbon and organic/boron polymer composites with different ratios of fibre volume contents. On the whole, the obtained accuracy of predicting the characteristics of the examined hybrid composites may be considered as acceptable for engineering applications.Published in Mekhanika Kompozitnykh Materialov, Vol. 30, No. 3, pp. 299–313, May–June, 1994.