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.     

Thermal deformation of unidirectionally reinforced hybrid composites. Report no. 1

Conclusion We conducted a dilatometric study of three types of hybrid unidirectionally reinforced composites (organic-glass-, organic-carbon-, and carbon-glass-fiber plastics), each of which was represented by several batches differing in the relative content of the two types of fibers. The tests were performed on a specially-designed laboratory prototype. It was shown that, for the materials studied, the coefficient of linear expansion can be controlled by means of hybridization — by combining several types of fibers with positive and negative values of the coefficient of linear expansion in one composite. Analytic expressions for the coefficient that were obtained by generalizing a three-phase model of a two-component composite with isotropic fibers to the case of a hybrid composite with anisotropic fibers satisfactorily describe the experimental data.Translated from Mekhanika Kompozitnykh Materialov, No. 2, pp. 229–236, March–April, 1989.     

Creep in unidirectionally reinforced polymer composites

Conclusions We have explored here the possibilities of predicting the permanent creep in unidirectionally reinforced polymer composite materials from the results of accelerated testing of their components. The mutually independent components of the viscoelastic compliance tensor under conditions of creep have been calculated with the aid of the Laplace transformation and an earlier verified variant of determining the mean elastic characteristics of a composite material, whereupon the originals of the sought functions have been obtained by a numerical inverse Laplace transformation. Experiments were performed with unidirectionally reinforced materials, a glass-plastic, an organoplastic, a carbon-plastic, and a boroplastic, all tested in tension in the direction of fiber reinforcement and in the transverse direction, also in longitudinal shear. The possibilities of predicting the creep in composite materials with the aid of functions characterizing the viscoelastic compliance of the binder and obtained by the method of temperature-time analogy have been confirmed twofold: by long-duration (up to 3 yr) control tests performed on the given materials and by control calculation of the creep in these composite materials from results of direct long-duration (up to 5 yr) tests performed on specimens of the binder.Translated from Mekhanika Kompozitnykh Materialov, No. 2, pp. 215–223, March–April, 1984.     

Thermal conductivity of reinforced media

On the basis of a model of an inhomogeneous body a solution is obtained for the problem of the temperature field and thermal conductivities of reinforced media, whose structure is formed by a doubly periodic system of n hollow cylinders of arbitrary diameter with the space between filled by a homogeneous medium. The thermophysical characteristics of the components are assumed given.Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 749–751, July–August, 1968.     

Longitudinal shear of unidirectionally reinforced plastics

The deformation and strength properties of undirectionally reinforced plastics in longitudinal shear are investigated. A law of shear deformation that takes into account the nonlinear properties of the matrix is established. Two modes of failure of the reinforced plastic are examined. The dependence of the shear strength of the plastic on the volume reinforcement content and the strength properties of the matrix is investigated.     

Thermal dependence of electric conductivity in thermoplastic composites

Thermal dependence of the electric conductivity of thermoplastic composites based on both amorphous (hiPS) and crystallized (PP) polymers is investigated in this study. Two types of carbon black fillers with different values of BET surface area were used as charge conductors. Composites based on crystallized polymer matrices indicate the sharp growth of electric resistivity just before the melting range. This maximum is followed by substantial decrease of resistance at T > T_melt. With the decrease of carbon black concentration both relative growth of resistance at the T T_melt and further dropping resistance at T > T_melt increase. Composites filled with particles of higher surface area are characterized by less pronounced matrix influence on thermal dependence of electric conductivity than composites filled with particles of lower surface area; this can be caused by more pronounced matrix/filler interaction in the first case. The range of temperatures at which the resistance increase occurs does not depend on the type of carbon filler and its concentration. Composites with amorphous matrices are characterized by distinct increase of resistance above glass transition. Thermal treatment of the sample significantly affects the initial values and intensity of the temperature dependence of the resistance.To be presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Published in Mekhanika Kompozitnykh Materialov, Vol. 31, No. 4, pp. 526–532, July–August, 1995.     

Thermal deformation of unidirectional hybrid composites. 2

Conclusions A variant of the solution of the problem of the thermorheologically complex temperature strain of a hybrid composite containing viscoelastic thermorheologically simple components with differing functions for temperature-time reduction in addition to elastic components, is proposed. An experimental study is conducted on unidirectional specimens of organic- and glass-fiber-reinforced plastic, organic- and carbon-fiber-reinforced plastic, and carbon- and glass-fiber-reinforced plastic at a constant rate of temperature change in the 20–150 °C range. Satisfactory correspondence is obtained between predicted and experimental data.For previous communication, see [1].Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 969–979, November–December, 1989.     

Thermal conductivity of micro-and nanostructural epoxy composites at low temperatures

The thermal conductivity of epoxy composites containing not only the traditional fillers quartz, talc, carbon black, and aerosil, but also the very promising carbon nanomaterials is investigated. Two kinds of carbon nanomaterials — multi-wall (MWNT) and single-wall (SWNT) carbon nanotubes — were considered. The influence of their content (from 0.05 to 3.0 wt.%) on the thermal conductivity of MWNT-epoxy composites was studied. The thermal conductivity of epoxy composites was examined in the temperature range from −150 to 150°C. It was found that the introduction of 0.1–1.0 wt.% MWNT enhanced the thermal conductivity of pure epoxy resin by about 40%. A further increase in content of the nanotubes decreased the thermal conductivity. This can be explained by the worsening of nanotube dispersion at their high concentrations. The maximum growth in the thermal conductivity of the epoxy composites, on the entire range of temperatures considered, was observed at a 0.1 wt.% content of MWNT. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 44, No. 1, pp. 117–126, January–February, 2008.     

Thermal deformation of a composite reinforced with hybrid cloth strips

Conclusion We tested (for mechanical and thermal effects) composites reinforced with hybrid cloth COS and VAI strips; five alternate schemes of material, which differred in terms of the content of VAI layers and layers reinforced with COS, were tested. The elasticity characteristics, tension diagrams, and CLTE of the composites were determined. It was established experimentally that variation in the relative content of the above-indicated layers makes it possible to regulate the thermal expansion of the composite in the longitudinal direction of the reinforcing strips Objectively over significant ranges; in this case, the elastic modulus varies negligibly, while the specific elastic modulus remains virtually unchanged,An alternate scheme for determining the elasticity characteristics and CLTE of laminar polymeric materials reinforced with hybrid cloth strips on the basis of component properties is developed. The model according to which the structural organization of the composite is subdivided into several levels is primarily a computational model. The stress-strain state of the repeating structural elements is evaluated by methods of the strength of materials. The proposed algorithm for computing the physicomechanical characteristics of laminar composites is implemented in the form of a computer program. The experimental elasticity characteristics and CLTE obtained for composites with a different content of COS and VAI layers are compared with those calculated in accordance with the method developed (the computed values correspond to the experimental with an accuracy acceptable for engineering applications).Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 392–401, May–June, 1988.     

Two-scale simulation of damage in unidirectionally fibre reinforced composite materials

The finite element analysis of engineering structures usually assumes a homogeneous as well as a continuous medium. The heterogeneity of matter, which is always found on a sufficiently small length scale is neglected by replacing the inhomogeneous medium through a model of a mathematically homogenized material. The macroscopic constitutive behaviour is derived from volume averaging procedures that smear the microscopic heterogeneities. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

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.