A composite material based on recycled tires

The present study is devoted to the elaboration and investigation of a composite material based on mechanically grinded recycled tires and a polymer binder. The correlation between the content of the binder, some technological parameters, and material properties of the composite was clarified. The apparent density, the compressive stress at a 10% strain, the compressive elastic modulus in static and cyclic loadings, and the insulating properties (acoustic and thermal) were the parameters of special interest of the present investigation. It is found that a purposeful variation of material composition and some technological parameters leads to multifunctional composite materials with different and predictable mechanical and insulation properties. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 45, No. 1, pp. 145–150, January–February, 2009.     

Damping properties of composites based on interpenetrating polymer networks formed in the presence of compatibilizing additives

From the results of an analysis of the viscoelastic characteristics of semi-interpenetrating polymer networks (semi-IPNs) that are based on a crosslinked polyurethane and a linear polystyrene and are formed in the presence of compatibilizing additives (oligourethane dimethacrylate and ethylene glycol monomethacrylate), their damping ability is est mated. Such parameters as the tangent of mechanical loss (tan δ) at the glass-transition temperature, the temperature interval of effective damping (where tan δ > 0.3), and the loss area under the loss modulus vs. temperature plots are used as the criteria of damping ability. It is shown that the introduction of the compatibilizing additives to the semi-IPNs extends the interval of their effective damping temperature. By varying the composition of the material and the amount of the compatibilizing additives, it is possible to realize a purposeful selection of vibration-damping materials for solving specific technological problems. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 4, pp. 545–558, July–August, 2006.     

Effect of thermal aging on the adhesive strength of joints of double-chain polymers with fibers and on the properties of unidirectional CFRPs based on them

The paper presents a study on the effect of thermal aging on the adhesive strength of joints of some double-chain polymers and fibers. It is shown that the initial shear strength of joints of a steel wire with double-chain polymers based on bisaminonitrile (R = −CH₂−) is significantly higher than that in the case of polymers based on the “A-B” monomer. The type of thermal stabilizer affects the strength of the fiber/matrix interface only slightly. Prolonged heating (up to 100 hours) of the joints at 350 °C does not reduce the strength of joints based on the “A-B” monomer, while that of joints based on bisaminonitrile decreases by 20-30%. The thermal stability of carbon-fiber-reinforced plastics appeared to be higher, which was likely due to the effect of scale factor. The strength of a test specimen batch decreased only upon exposure to 400 °C for more than 100 hours.     

Effect of surface modification of fibers with a polymer coating on the interlaminar shear strength of a composite and the translation of fiber strength in an F-12 aramid/epoxy composite vessel

The surface of aramid fibers was modified with a polymer coating — a surface treatment reagent containing epoxy resin. The resulting fibers were examined by using NOL tests, hydroburst tests, and the scanning electron microscopy. The modified fibers had a rougher surface than the untreated ones. The interlaminar shear strength of an aramid-fiber-reinforced epoxy composite was highest when the concentration of polymer coating system was 5%. The translation of fiber strength in an aramid/epoxy composite vessel was improved by 8%. The mechanism of the surface treatment of fibers in improving the mechanical properties of aramid/epoxy composites is discussed. Russian translation publeshed in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 6, pp. 729–738, November–December, 2006.     

Influence of Moisture on the Structure and Properties of the Interphase Layer of a Composite Based on an Epoxy Binder with a Disperse Filler

Properties of a model composite based on an ED-22 epoxy binder, cured with polyprophylene polyamine, and disperse LiF crystals as a filler were investigated by the methods of dilatometry and X-ray diffractometry. It was established that the density of cross-links of the epoxy binder in the interphase layer was lower than in a block specimen. Therefore, the thermal expansion of the composite on heating to 120°C, in terms of that of the binder, grew significantly with the degree of filling ϕ, and the water uptake also increased at the initial stage. The presence of absorbed water led to considerable changes in the structure and properties of the composite interphase: the binder became more cross-linked, its structural ordering decreased, the thermal expansion at heating diminished by a factor of 3. 7 (at ϕ = 50%), and the glass-transition temperature increased. As a result of long-term action of moisture, changes in the internal stresses had an extreme character.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 535–544, July–August, 2005.     

Formation of a transition layer on the fillers of polymer composites

Based on a plane model of composites, the effect of a transition layer on the elastic modulus E_c of the composites is analyzed in the case where, under the action of a load, the transition layer is formed both on the side of matrix and filler. In evaluating E_c, it is assumed that the elastic modulus in the layer grows linearly from the elastic modulus of matrix to that of filler, but pores in the filler are impermeable to matrix macromolecules. Analytic relation ships are found which allow one to determine the volume fractions of the transition layer on the side of matrix and filler if the experimental elastic modulus of the composite is known. These relationships are used to find the magnitude of the layer in epoxy composites with various fillers and to evaluate its effect on the compressive elastic modulus of the composites. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 693–700, September–October, 2006.     

Experimental studies on the adhesion strength of a polymer-metal bond depending on the contact zone geometry

Theoretical investigation of the stress-strain state at special points of constructions, e.g., in adhesion joints, has demonstrated that the stress state in the contact zone strongly depends on the configuration of the zone. In order to verify these results, some experiments were carried out. Cylindrical polymer specimens having a circular groove at one of its ends were cemented to steel mushrooms and tested for abruption in tension and cantilever bending. The experiments showed that the adhesive strength depended on the profile of the joint and had a maximum at the optimum value of the angle of the joint and a minimum when the groove was absent. The ratio between the maximum and minimum strength values was 1.5 in tension and 2.5 in bending. The greater effect in the latter case can be explained by the high gradient of the stresses in bending. The experimental results confirmed the possibility of controlling the adhesive strength by changing the contact geometry in accord with the stress-strain calculations.Institute of the Mechanics of Continuous Media, Russian Academy of Sciences, Perm', Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 4, pp. 493–498, July–August, 1999.     

A Study of the Relation between the Mechanical Properties and the Adhesion Level in a Laminated Packaging Material

The mechanical properties of a laminate consisting of aluminum-foil, adhesive, and polymer layers were studied in relation to the adhesion level. A special application for liquid-food packaging materials was considered. In experiments, laminates with and without adhesive layers were tested. Tensile tests were first run for every layer of the laminate, and the data obtained were then used in analyzing the results of tensile tests on the entire laminate, as well as in theoretical and finite-element calculations. Relations between different mechanical properties (such as Young's modulus, the peak stress, and the strain at the peak stress) and the adhesion level were analyzed. It was found that the tensile strength and the strain at the peak stress increased with adhesion level. Only slight differences in Young's modulus were observed at different adhesion levels.     

Markov model of connection between the distribution of static strength and fatigue life of a fibrous composite

Within the framework of a unified mathematical model based on the Markov chain theory, an attempt is made to describe the distribution of static strength, the fatigue curve, and the accumulation of fatigue damages. It is assumed that the fatigue failure of a test specimen occurs after the destruction of some its critical microvolume consisting of two — elastic (brittle fibers) and plastic (matrix) — parts. In the second part, plastic strains accumulate as soon as the cyclic load exceeds some level. Numerical examples are presented. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 615–630, September–October, 2006.     

Environmental Effects on the Mechanical Properties of Glass-FRP and Aramid-FRP Rebars

In the paper, the experimental results on the effect of temperature and moisture on the mechanical properties of FRP (Fiber-Reinforced Polymer) reinforcements are presented. FRP rebars made from glass and aramid fibers were subjected to cyclic thermal actions at temperatures ranging between 20 and 70°C, typical of natural hot-climate environments. Tensile tests were also carried out on FRP rebars. The effect of moisture was investigated by cyclic wetting and drying the FRP rebars under laboratory conditions before their testing in tension. Finally, the elastic modulus and tensile strength of the FRP rebars exposed to these cyclic actions were compared with those obtained for unexposed ones, in order to evaluate the mechanical damage caused by environmental conditions.     

Variation of the structure and permeability of tensioned fiber layers during impregnation with a thermoplastic polymer melt

The influence of displacements of tensioned fibers on the impregnation of fibrous layers with a polymer melt and on the final composite structure is studied. Using computer simulation, it is shown that, during impregnation, the structure of tensioned fibrous layers changes considerably depending on the initial arrangement and tensioning of fibers. The consolidated regions formed under the melt front move inside the impregnated layer with the advancing melt front. Displacement of the tensioned fibers as well as the formation of “washouts” favors the impregnation of internal layers, but cause significant inhomogeneity of the polymer structure. The surface (on the side of the melt flow) regions are more saturated with the polymer than the internal ones. A difference in the melt percolation mechanisms at various impregnation regimes is revealed. The effective permeability coefficients of a tensioned fiber layer are not constant but depend on the conditions and regimes of impregnation. Submitted to the 11th Conference on the Mechanics of Composite Materials (Riga, June 11–15, 2000). Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 2, pp. 259–270, March–April, 2000.     

Correlation between the mechanical properties and the amount of desorbed water for composites based on a recycled low-density polyethylene and linen yarn production waste

The effect of the amount of sorbed water on the mechanical properties (tensile modulus, tensile strength, unit work of fracture, and characteristic strains) of composites based on a recycled low-density polyethylene, both unmodified and modified with diphenylmethane diisocyanate (DIC), is an a lyzed by statistical methods. The results of tensile tests are found to depend on the amount of sorbed water considerably. The elastic modulus, the unit work of fracture, and the characteristic strains correlate linearly with the amount of water. It is found that the elastic modulus drops after the sorption of water, but then, during the desorption process, it is restored gradually and reaches its initial value after a 30-day drying. This is explained by the plasticizing effect of water on composite materials containing hydrophilic natural fibers. DIC improves the interfacial interaction of the fiber-matrix interface and slows down the desorption of water. The investigations of the main deformational and strength characteristics of the unmodified and modified systems showed that the ad verse effect of water completely disappeared after a 30-day drying. The same conclusion, with a 95% probability, can be drawn from the results of an analysis of variance (ANOVA). __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 5, pp. 626–638, September–October, 2007.     

Composites based on cellulose fiber nonwovens and a water soluble polymer 1. Structure and strength-deformation characteristics of cellulose fiber nonwovens and structural characteristics of the composites

The results of a study on the strength-deformation characteristics (tensile elastic modulus, ultimate strength, elongation at break, and punching and tearing strengths) of two kinds of cellulose fiber nonwovens (CFNs) with dissimilar void content and different geometrical parameters of cellulose fibers are discussed. The structural characteristics of composites prepared by impregnation with poly(vinyl alcohol) water solutions are analyzed, too. Composites with volume fractions of polymer up to 0.4% and volume fractions of voids up to 0.3% were prepared. Filling of voids by the polymer occurred without significant changes in the structure of CFNs. The fraction of closed voids increased with polymer content.     

On the equivalence of non‐iterative transformation methods based on scaling and spiral groups

The non‐iterative numerical solution of nonlinear boundary value problems is a subject of great interest. The present paper is concerned with the theory of non‐iterative transformation methods (TMs). These methods are defined within group invariance theory. Here we prove the equivalence between two non‐iterative TMs defined by the scaling group and the spiral group, respectively. Then, we report on numerical results concerning the steady state temperature space distribution in a non‐linear heat generation model. These results improve the ones, available in the literature, obtained by using the invariance with respect to a spiral group. Copyright © 2009 John Wiley & Sons, Ltd.     

转移概率流图的概率理论基础与应用方法(Ⅵ)——中止规则对调整型抽样方案复合OC函数影响的进一步讨论

解顺强．转移概率流向图的概率理论基础与应用方法（Ⅵ）—中止规则对调整型抽样方案复合ＯＣ函数影响的进一步讨论．数理统计与管理．１９９８．１７（６）本文运用转移概率流向图及其粘接方法，证明了当检查始于加严抽样方案时，不带中止规则的调整型抽样方案与带中止规则的相应的调整型抽样方案，两者的复合ＯＣ函数相同     

The influence of water sorption-desorption cycles on the mechanical properties of composites based on recycled polyolefine and linen yarn production waste

The effect of water on the mechanical properties (tensile modulus, ultimate tensile strength, tensile strain, and specific work at break) of both chemically treated and untreated composites based on a recycled low-density polyethylene and linen yarn production waste is analyzed. It is found that three water sorption-desorption cycles change the tensile properties of both the materials irreversibly. This effect is considered as the result of partial fracture of the fiber-matrix interface. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 6, pp. 839–848, November–December, 2007.     

Mathematical modelling and the study of the influence of initial stresses on the SIF and ERR at the crack tips in a plate-strip of orthotropic material

A plate-strip fabricated from the orthotropic material and containing a crack whose edges are parallel to the face planes of the plate is considered. It is assumed that the strip is stretched (or compressed) initially along the crack edges by uniformly distributed external normal forces acting on the simply supported ends of the plate-strip. After this initial stretching (or compression) the crack edges are loaded by additional uniformly distributed normal (opening) forces. As a result of the action of these additional forces the stress concentration characterized by the stress intensity factor (SIF) of mode I or by the energy release rate (ERR) of mixed mode arises at the crack tips. In this paper, the influence of the initial stresses on the SIF or ERR is modelled mathematically by the use of the three-dimensional linearized theory of elasticity. The aim of the present investigations is to study the effect of the mechanical–orthotropic properties of the plate-strip material on this influence by the use of the finite element method (FEM) modelling of the corresponding boundary-value problem.