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.     

Overequilibrium heating of the surface of a heat-shield tile in a subsonic jet of dissociated air

The results of measuring and numerically calculating the surface temperature distributions of heat-shield tiles with uniform and nonuniform catalytic coatings exposed to subsonic dissociated-air flows in an induction plasmotron are presented. The measurements are consistent with the calculated surface temperature profiles obtained from a numerical solution of the Navier-Stokes equations for a chemical-nonequilibrium flow of dissociated nitrogen. The results are compared with the data of a space shuttle flight experiment on the effect of a discontinuity of heat shield catalyticity on the overequilibrium surface temperature jump.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 144–150, May–June, 1991.     

Properties of rigid polyurethane foams filled with milled carbon fibers

The effect of milled carbon fibers of two types (differing in length) on the properties of rigid polyurethane foams in the density range from 50 to 90 kg/m³ is investigated. The coefficient of thermal expansion and properties of the foams in tension and compression as functions of fiber content in them are determined. It is found that the long fibers are more efficient in improving the properties of the foams in their rise direction. The elongation at break of the foams decreases significantly with increasing fiber content.     

Increased heat transfer to a titanium surface with oxygen injection into the nonequilibrium boundary layer

The results of an experimental and numerical investigation of the heat transfer between a subsonic jet of dissociated nitrogen and a titanium surface, through which molecular oxygen is blown into the jet, are presented. It is established that in the nonequilibrium boundary layer regime the dependence of the heat flux on the injected oxygen flow rate is nonmonotonic. At a certain flow rate the heat transfer to the titanium surface reaches a maximum that considerably exceeds (by 20%) the heat transfer to an impermeable wall. The observed increase in heat transfer in the presence of injection is attributed to the interaction of the gas-phase exchange reactions and the recombination of atoms on the titanium surface, which has sharply different catalytic properties with respect to the recombination of nitrogen and oxygen atoms.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 148–155, July–August, 1991.     

Flow and Heat Transfer in Underexpanded Air Jets Issuing from the Sonic Nozzle of a Plasma Generator

We present the results of an experimental investigation and numerical simulation of the gasdynamic structure of underexpanded dissociated-air jets and the heat transfer in these strongly nonequilibrium flows under the test conditions realized in the 100-kW electrodeless VGU-4 plasma generator of the Institute for Problems in Mechanics of the Russian Academy of Sciences (IPM RAS). The flow and heat transfer analysis is carried out on the basis of measurements of the static pressure in the plenum chamber, at the sonic nozzle exit, and on the low-pressure chamber wall, the stagnation pressure on the jet axis using a Pitot tube, and the heat transfer at the stagnation points of water-cooled models placed along the jet axis. The numerical simulation, based on complete Navier-Stokes equations, includes the calculation of (1) equilibrium air plasma flows in the discharge channel of the VGU-4 plasma generator; (2) underexpanded nonequilibrium dissociated-air jet outflow into the ambient space; and (3) axisymmetric jet flow past cylindrical models.     

Physicomechanical Characteristics of Spray-On Rigid Polyurethane Foams at Normal and Low Temperatures

The effect of processing factors on the inhomogeneity and physicomechanical characteristics of spray-on polyurethane foams is studied. The dependences of the basic characteristics of foam plastics on the apparent density and cell-shape factor are determined. A method is offered for evaluating the effect of the technological surface skin on the tensile characteristics of foam plastics under normal and low temperatures.     

Some characteristics of the ablation of decomposing materials

The authors examine a most simple model of mass transfer from the heated surface of a condensed phase in the presence of chemical reactions. It is shown that decomposition of the molecules of starting substance and subsequent vaporization (or sublimation) of the decomposition products have an important influence on this process and lead to the appearance of a number of new effects not observed in the ablation of nondecomposing materials. The principal conclusions of the theory are confirmed qualitatively by the experimental data, on the degradation of certain polymers in a high-enthalpy gas jet described in the concluding section of the paper.The authors thank G. I. Barenblatt for his interest in their work.     

Analysis of phenomenological models describing the catalytic properties of high-temperature reusable coatings

The possibilities of using phenomenological models, constructed on the basis of the ideally-adsorbed Langmuir layer theory, to describe the catalytic properties of the heat shield coatings of reusable hypersonic vehicles are analyzed on the basis of a comparison of the calculated heat flows and the effective catalytic activity coefficients with full-scale and laboratory experimental data.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 133–144, November–December, 1996.     

Radiational properties of the decomposition products of a model around which flows a subsonic high-temperature plasma stream

Models made of an asbestos plastic were tested in a subsonic jet of air heated to T = 8500 °K with p = 1 atm. The multicomponent thermal boundary layer arising at the decomposing surface of the model has a complex structure. At the surface of the model, in the critical region of the boundary layer, there is a sublayer with an extension of 1.5-2 mm where the temperature of the gas is constant and its composition is unchanged to a great degree and is mainly determined by the decomposition products of the asbestos plastic. In this region the spectral distribution of the intensity of the radiation of the vapors of the asbestos plastic was obtained in a range of 0.3-0.9, which makes it possible to calculate the spectral coefficients of absorption for a temperature of 3500 °K. The radiating power of the vapors is compared with the radiation of an air plasma of the oncoming flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 76– 80, November–December 1978.The authors are indebted to Yu. K. Rulev for his aid in carrying out the experiment.