Long-Term Durability of Glass-Fiber-Reinforced Composites under Operation in Pulp and Reactant Pipelines

Composite pipes 215 mm in diameter with a 6-mm wall, 3-mm functional layer, and ±60° glass-fiber-reinforced plastic (GFRP) layers were examined by means of microstructural analysis and mechanical testing. Three types of pipes were considered: unused, after a five-year operation at a pressure of 0.6 MPa and temperature of 70°C, and after a five-year operation at 0.6 MPa and 20°C. The GFRP load-carrying layer and the interfaces were investigated by a metallographic optical microscope, a computerized microscanning equipment, and a software image processing package. The initial and accumulated damages in the microstructure of the composite and interfaces were examined. The mechanical properties of the pipes after a long-term operation were examined on two-layer specimens in three-point bending. The stiffness and strength characteristics were measured in the axial and circumferential directions under tensile and compressive loads at elevated temperatures. Composite pipes, 8 m in length and 215 mm in diameter, were simulated numerically as shells of revolution. The shell model was corrected by a refined Timoshenko theory and a dual-modulus temperature-dependent model of stiffness for the multilayer composite structure. The strength margin of the composite pipes was determined based on real strength properties.     

Contributions to the mathematics of the nonstandard finite difference method and applications

We formalize the transfer of essential properties of the solution of a differential equation to the solution of a discrete scheme as qualitative stability with respect to the properties. This permits us to motivate some rules (viz. on the order of the difference equation, on the renormalization of the denominator of the discrete derivative, and on nonlocal approximation of nonlinear terms) used in the design of nonstandard finite difference schemes. Extensions of some models are considered, and numerical examples confirming the efficiency of the nonstandard approach are provided. © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17: 518–543, 2001     

Cross-Linked Thermoplastic Blends of Polyethylene with an Elastomer. 1. Deformation and Strength Characteristics

Results of an experimental investigation into changes of some mechanical characteristics of binary blends of high- and low-density polyethylenes with an elastomer (ethylene-propylene-dicyclopentadiene terpolymer) in the course of -radiation and chemical cross-linking are reported for a wide range of component ratios. Data on changes in the tensile strength and total, residual, and reversible strains at break, as well the microhardness and other characteristics are obtained. The effect of component ratio and cross-linking on these characteristics is discussed.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. -, March–April, 2005.     

A new method of proving structural properties for certain class of stochastic dynamic control problems

This paper introduces the multimodularity concept to study structural properties for certain class of stochastic dynamic control problems through a new efficient approach. We demonstrate that this approach can substantially simplify the proofs of the main results of one recent article and provide an alternative method for two other models in the literature.     

Cross-Linked Thermoplastic Blends of Polyethylene with an Elastomer 2. Some Structural Characteristics and Their Relationship with Mechanical Properties

Results of an experimental investigation into the changes of some structural characteristics of binary blends of high-density polyethylene and low-density polyethylene with an elastomer (ethylene-propylene-dicyclopentadiene terpolymer, EPDM) in the course of γ-radiation and chemical cross-linking are reported for a wide range of component ratios. The data on changes in the crystallinity, density of the blends, content of the cross-linked part, as well the correlation of these characteristics with some mechanical properties, are discussed. Suggestions are put forward about the possibility of formation of a combined amorphous PE-EPDM phase with a higher structural arrangement than that in the individual components.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 545–562, July–August, 2005.     

Correlation between the Mechanical Properties and the Amount of Desorbed Water for Composites Based on Low-Density Polyethylene and Linen Yarn Production Waste

The effect of the amount of desorbed water on the mechanical properties of composites based on low-density polyethylene and linen yarn production waste (LW) is analyzed by statistical methods. It is shown that the amount of absorbed water decreases during the desorption process at room temperature both for specimens modified and unmodified with diphenylmethane diisocyanate (DIC.) The most sensitive to the action of water is the elastic modulus, which decreases considerably under the effect of water and is fully restored in the desorption process. The tensile strain also increases with the amount of absorbed water. It is found that the elastic modulus of the unmodified composite correlates linearly with the amount of desorbed water. Between the amount of desorbed water and the tensile strain, as well the specific work of deformation, a negative linear correlation is revealed. After water desorption, all strength and deformation characteristics of both the modified and unmodified composites are fully recovered.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 515–524, July–August, 2005.     

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.     

Compliance of a Biocomposite Vascular Tissue in Longitudinal and Circumferential Directions as a Basis for Creating Artificial Substitutes

Experimental studies on the mechanical behavior of 11 human common carotid arteries at different values of internal pressure and axial force were performed on a device allowing us to measure the internal pressure, axial force, and circumferential and longitudinal deformations of the vessel. The persons age ranged from 20 to 28 years. Two types of experiments were carried out. In the first series, cylindrical samples were gradually loaded by an internal pressure from 0 to 200 mmHg at different longitudinal stretch ratios. The second series included axial extension of the same samples at different circumferential stretch ratios. The undulation level of elastin membranes in longitudinal and circumferential directions for samples fixated at different values of internal pressure and longitudinal stretch ratio were determined from histological data.