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Showing papers by "Vikram Sarabhai Space Centre published in 1993"


Journal ArticleDOI
TL;DR: In this article, a linear dependence of the logarithm of the Arrhenius temperature integral ln p(x) on x (= E R T ), its slope on x−1 and its intercept on In x, respectively, has been derived for non-isothermal experiments.

101 citations


Journal ArticleDOI
TL;DR: In this article, the effects of fiber loading and fiber length on the viscoelastic properties of polyethylene reinforced with short pineapple fibers, extracted from pineapple leaves, have been studied as a function of temperature at different fiber orientations.

50 citations


Journal ArticleDOI
TL;DR: In this article, the first observations of mean winds and the amplitude and phases of the tidal components measured with a meteor wind radar located at Trivandrum (8.5°N, 77°E) during five consecutive days of counter electrojet events identified in the horizontal component of the earth's magnetic field from January 27-31, 1987 are described.
Abstract: The first observations of mean winds and the amplitude and phases of the tidal components measured with a meteor wind radar located at Trivandrum (8.5°N, 77°E) during five consecutive days of counter electrojet events identified in the horizontal component of the earth's magnetic field from January 27–31, 1987 are described. The mean zonal winds in the altitude region of 90–105 km are in general westward during counter electrojet days and eastward during no counter electrojet days. The amplitudes and phases of the tidal components on the counter electrojet days are found to be substantially different from those on the no counter electrojet days.

47 citations


Journal ArticleDOI
TL;DR: A series of hydroxyl-terminated polybutadience (HTPB) resins, manufactured by free-radical polymerisation using a peroxide initiator, was used in propellant formulation experiments with a view to studying the resin production variables and their influence on the resultant propellant properties as mentioned in this paper.
Abstract: Composite propellants based on hydroxyl-terminated polybutadience (HTPB) resin are the most common contemporary solid propellants for launch vehicle and missile applications. A series of HTPB resins, manufactured by free-radical polymerisation using a peroxide initiator, with varying molecular weights and hydroxyl values, was used in propellant formulation experiments with a view to studying the resin production variables and their influence on the resultant propellant properties. It is seen that HTPB resins with a wide range of hydroxyl values could be effectively utilized in propellant formulations. Also, propellants with higher strain capability and chain flexibility could be produced from lower hydroxyl value resins. © 1993 John Wiley & Sons, Inc.

46 citations


Journal ArticleDOI
TL;DR: In this article, a systematic study has been conducted on different batches of hydroxylterminated polybutadiene (HTPB) -based composite solid propellants, where the ratio of chain extender to crosslinker was systematically varied, with a view to achieving the maximum possible strain capability and moderately high tensile strength, keeping all other parameters constant.
Abstract: There has been a constant endeavor to improve the mechanical properties of hydroxylterminated polybutadiene (HTPB) -based composite solid propellants. A systematic study has been conducted on different batches of HTPB resins with varying molecular weights and hydroxyl values. Propellant formulation experiments were conducted wherein the ratio of chain extender to crosslinker was systematically varied, with a view to achieve the maximum possible strain capability and moderately high tensile strength, keeping all other parameters constant. The influence of increasing hydroxyl content from trimethylolpropane at the expense of hydroxyl content from butanediol, on the mechanical properties of the finished propellant, has been depicted on 3-dimensional graphs. The isoproperty lines, plotted as a triangular chart with the percentage hydroxyl contents from the three constituents, can be used to arrive at the suitable formulation for a specified application depending upon the OH value of the resin. HTPB resins with high molecular weight, low functionality, and low hydroxyl value require higher levels of trifunctional curing agent and higher NCO / OH ratios to obtain outstanding mechanical properties, especially elastic properties, compared to low molecular weight, high functionality resins. The impact of hard and soft segment domain structure on the mechanical behavior of the cured systems is more pronounced in the low molecular weight resin formulations due to the higher hard segment content compared to those attainable in high molecular weight resin formulations. © 1993 John Wiley & Sons, Inc.

41 citations


Journal ArticleDOI
TL;DR: In this article, the effects of sea breeze on optical depth, size distribution, and columnar loading of aerosols at the tropical coastal station of Trivandrum are studied.
Abstract: The effects of sea breeze on optical depth, size distribution, and columnar loading of aerosols at the tropical coastal station of Trivandrum are studied. It has been observed that sea-breeze front activity results in a significant and short-lived enhancement in aerosol optical depth and columnar loading in contrast to the effects seen on normal sea-breeze days. Examination of the changes in columnar aerosol size distribution associated with sea-breeze activity revealed an enhancement of small-particle (size less than 0.28 [mu]m) concentration. The aerosol size distribution deduced from optical depth measurements generally show a pronounced bimodal structure associated with the frontal activity. 22 refs., 12 figs., 1 tab.

40 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of various pre- and post-weld heat treatments on Ti-6Al-4V alloy has been investigated and it was shown that high temperature annealing of the welded samples does not increase the tensile ductility but improves the toughness at both the fusion zone and the heat affected zone.
Abstract: This paper represents a summary of experimental work carried out to find the effect of various pre- and post-weld heat treatments on Ti-6Al-4V alloy. In the as-welded state the samples exhibit about 80% of the tensile ductility and about 90–95% of the impact/fracture toughness of the base metal. Low temperature stress relieving or ageing carried out subsequent to the welding operation improves the tensile properties but decreases the toughness at the fusion zone. Solution treatment followed by welding and ageing or the post-weld solution treatment and ageing treatment leads to only a marginal increase in tensile strength at the expense of toughness at the fusion zone. High temperature annealing of the welded samples does not increase the tensile ductility but improves the toughness at both the fusion zone and the heat affected zone. The above facts and a special burst-pressure test conducted on a gas bottle in the as-EB welded state show that Ti-6Al-4V components can be used without subjecting them to any post-weld heat treatments.

39 citations


Journal ArticleDOI
TL;DR: In this article, wind measurements using a meteor trail radar which performed during two June solstice and three December solstice months were analyzed to study the tidal winds over Trivandrum (8.5°N).

28 citations


Journal ArticleDOI
TL;DR: In this article, the spectral properties of wind velocity and temperature at Thumba, a site on the western coast of India, were studied using data from an instrumented tower, sodar and long-period temperature data available for the site.
Abstract: The features of the spectra of meteorological fields of wind velocity and temperature observed at Thumba, a site on the western coast of India, are discussed. Data utilized for the study are mostly from an instrumented tower, sodar and long-period temperature data available for the site. The influence of local circulations like the sea breeze is manifested also in the general spectral characteristics of horizontal wind, as with the spectral gap in the mesoscale region between the synoptic-scale region and the turbulent-scale region of the spectra. The width of the spectral gap observed between the wave-active region and the microscale region in the wind velocity spectra is seen to be dependent on the stability of the medium, and the gap is found to shift to the high-frequency side with increasing stability. The composite spectrum of temperature also reveals a prominent gap at about an hour. It is seen that with the advection of a sea breeze over the land, a shallow thermal internal boundary layer is formed and regions above one tenth of this depth obey mixed-layer similarity.

26 citations


Journal ArticleDOI
TL;DR: In this paper, the thermal post buckling behavior of simply-supported, antisymmetric cross-ply plates with immovable edges is investigated and conditions under which the thermal buckling in the classical sense occurs are derived.
Abstract: The thermal post buckling behavior of simply-supported, antisymmetric cross-ply plates with immovable edges is investigated in this paper. For this purpose, a one term approximation for the inplane and transverse displacements is assumed and Rayleigh-Ritz method is used to obtain the equations of equilibrium. The question, whether the true thermal buckling (bifurcation buckling under thermal loads) exists for such plates is also addressed to. The conditions under which the thermal buckling in the classical sense occurs are derived. It is shown that nonlinear bending stiffness for such plates is direction dependent, because of an extra quadratic nonlinear term in addition to the usual cubic nonlinear term in the governing equilibrium equation. Results are presented for various plate configurations.

21 citations


Journal ArticleDOI
TL;DR: In this article, small winged, transparent, platy crystals of uric acid of about 0.5x0.1 mm were grown and were found to be hydrated uric acids.

Journal ArticleDOI
TL;DR: In this article, the effect of mixing on the extent of pseudoplasticity has been represented in the form of a bar chart and a correlation in terms of shear and yield stresses has been developed for viscosity index.
Abstract: The effect of mixer blade speed and mixing cycle time on the rheological behaviour of an optimized HTPB-based propellant formulations has been studied keeping the temperature constant. Variations in yield stress and viscosity at unit shear rate have been determined as a function of time for different mixing speeds. The effect of mixing on the extent of pseudoplasticity has been represented in the form of a bar chart. A correlation in terms of shear and yield stresses has been developed for viscosity index, i.e., the viscosity at unit shear rate as a function of mixer blade speed.

Journal ArticleDOI
TL;DR: In this paper, a mixture of hydroxy-terminated polybutadiene (HTPB) liquid prepolymers (I-IX) were synthesized by H2O2-initiated free-radical polymerization of butadiene in an isopropanol-water solvent system.
Abstract: Hydroxy-terminated polybutadiene (HTPB) liquid prepolymers (I-IX), with closely similar OH values, Mn, viscosity, and microstructure, were synthesized by H2O2-initiated free-radical polymerization of butadiene in an isopropanol–water solvent system. However, binders obtained by curing HTPB polymers showed wide variations in their sol content, cross-link density, and mechanical properties. These variations were atributed to the differences in functionality-type distribution (FTD) and molecular weight distribution (MWD) of the polymers. FTD was interpreted in terms of -type primary hydroxyls. [V/G] showed excellent linear correlation with the elongation at break (E) of the binders. The polymers exhibited bimodal MWD and this behavior was discussed in relation to two different initiation processes occurring. The high molecular weight fraction (Fh) of the various polymers was determined by reverse-phase HPLC and showed good correlation with E. The sol content and cross-link density of the binders also showed good correlation with the parameter V/GFh. The parameters [V/G] and Fh provide acceptance criteria for blending different batches of polymers for propellant formulations. © 1993 John Wiley & Sons, Inc.

Journal ArticleDOI
TL;DR: In this paper, large amplitude free vibrations of simply supported rectangular cross-ply plates are examined and the restoring force function is found to be a cubic polynomial, giving a Duffing type equation, or a combination of quadratic and cubic terms.

Journal ArticleDOI
TL;DR: In this paper, a four noded rectangular finite element, having 14 degrees of freedom per node, based on a simple higher-order theory is developed to investigate the large deflection behavior of composite plates.

Journal ArticleDOI
01 Mar 1993-Polymer
TL;DR: In this paper, thin films of polypyrrole doped with polymeric nickel phthalocyanine were grown on a platinum substrate by the electrochemical oxidation of pyrrole from aqueous solution containing 0.01 M Pyrrole and 0.1 M sodium salt.

Journal ArticleDOI
TL;DR: In this article, the E and F region electric field fluctuations are found to be well correlated; the estimated correlation coefficient is in the range of 0.52-0.8, with F region components stronger than those of the E region by a factor of about 1.5 on the average.

Journal ArticleDOI
TL;DR: In this paper, copper phthalocyanine containing peripheral carboxyl groups has been converted into the corresponding polyimides by condensing the anhydride of the latter with 4,4′-diaminodiphenyl ether.

Journal ArticleDOI
TL;DR: In this article, finite element results for the postbuckling behavior of circular plates resting on an axi-symmetric elastic partial foundation are presented, and different configurations of foundations are considered to evaluate the linear critical loads and nonlinear loads.

Journal ArticleDOI
TL;DR: In this article, an analytical theory for short-term orbit motion of satellite orbits with Earth's zonal harmonics was developed in terms of KS elements, which can be used for accurate onboard computation of state vector in navigation and guidance packages.
Abstract: Analytical theory for short-term orbit motion of satellite orbits with Earth's zonal harmonicsJ 3 andJ 4 is developed in terms of KS elements. Due to symmetry in KS element equations, only two of the nine equations are integrated analytically. The series expansions include terms of third power in the eccentricity. Numerical studies with two test cases reveal that orbital elements obtained from the analytical expressions match quite well with numerically integrated values during a revolution. Typically for an orbit with perigee height, eccentricity and inclination of 421.9 km, 0.17524 and 30 degrees, respectively, maximum differences of 27 and 25 cm in semimajor axis computation are noted withJ 3 andJ 4 term during a revolution. For application purposes, the analytical solutions can be used for accurate onboard computation of state vector in navigation and guidance packages.

Journal ArticleDOI
TL;DR: In this article, a quantitative analysis is made of the amplitudes and phases of the annual and semiannual oscillations in the zonal wind in the equatorial stratosphere and lower mesosphere, using the rocket data in the 20-80 km region at three stations, Thumba, Kwajalein, and Ascension Island which are around ±8° latitude, but at different longitudes.

Journal ArticleDOI
TL;DR: In this article, a simple one-dimensional finite element involving only out-of-plane deformation and its derivative is developed to investigate the buckling of tapered orthotropic circular plates.

Journal ArticleDOI
TL;DR: In this article, an approach for estimating the average molecular weight between crosslinks (Mc) from the functionality distribution of hydroxyl-terminated polybutadiene (HTPB) was proposed.
Abstract: A novel approach is proposed for estimating the average molecular weight between crosslinks (Mc) from the functionality distribution of hydroxyl-terminated polybutadiene (HTPB). The functionality distribution of four free-radically polymerised HTPB prepolymers of varying hydroxyl content and molecular weight was determined by a combination of preparative and analytical gel permeation chromatography. The gumstock properties of the samples cured with stoichiometric amounts of toluene diisocyanate were not correlatable with the relative amounts of difunctional chain extender and multifunctional crosslinker present, unlike the case of HTPB with similar hydroxyl content and molecular weight. However, the mechanical properties and sol content could be correlated with the average molecular weight between crosslink sites, Mc, of the cured polymer. The Mc values derived by our method compare well with those of classical methods, and the observed differences are attributed to segmental entanglement. These Mc values give consistently good correlation with all the gumstock properties, confirming the validity of our approach and the soundness of the techniques developed for the determination of the functionality distribution of HTPB.

Journal ArticleDOI
TL;DR: In this paper, a multi-director displacement field approach was used to describe the geometry of a multilayered sandwich shell and the linear theory was used for the analysis of the transverse warping of a cross-section due to the shear deformation and fibre compressibility of each layer.

Journal ArticleDOI
TL;DR: In this article, a photocrosslinkable polymethacrylate system with enhanced thermal stability and solvent resistance was synthesized, which exhibited enhanced solvent resistance and thermal stability compared with the unmodified polymer.
Abstract: Novel photocrosslinkable polymethacrylate systems with enhanced thermal stability and solvent resistance were synthesized. Copolymers of methyl methacrylate (MMA) or butyl acrylate (BuA) with 4-maleimido benzoic acid (MBA) were synthesized and photocrosslinkable methacrylic functions were incorporated through the pendent COOH groups. Photofunctional groups were introduced by the acid chloride route and by the epoxy-carboxy reaction. Photocrosslinking was performed using UV radiation of 350 nm in the presence of a photo-initiator. The kinetics of photocuring was studied with a model multiacrylate. The imide-modified photocured acrylate polymer exhibited enhanced solvent resistance and thermal stability, compared with the unmodified polymer. Neuartige photovernetzbare Polymethacrylate mit verbesserter thermischer Stabilitat und Losungsmittelbestandigkeit wurden hergestellt. In Copolymere aus Methylmethacrylat (MMA) oder Butylacrylat (BuA) mit p-Maleimidobenzoesaure (MBA) wurden photovernetzbare Methacrylfunktionen uber die endstandigen COOH-Gruppen eingebaut. Photofunktionelle Gruppen wurden uber die Saurechloridroute und die Epoxy-Carboxy-Reaktion eingefuhrt. Die Photovernetzung wurde mittels UV-Strahlung bei 350 nm in Gegenwart eines Photoinitiators durchgefuhrt. Die Kinetik der Photohartung wurde an einem Multiacrylat untersucht. Das Imid-modifizierte gehartete Polyacrylat wies gegenuber dem nicht modifizierten Polymeren verbesserte thermische Stabilitat und Losungsmittelbestandigkeit auf.

Journal ArticleDOI
TL;DR: In this paper, the vertical profiles of tidal components obtained from these observations are compared with the theoretically obtained tidal fields, and there is agreement between the observational and theoretical profiles, especially in August 1976 and April 1980, but there are significant differences between the two in certain height ranges.
Abstract: Making use of time series data obtained by M-100B rockets at Trivandrum (8.5°N, 77°E) in August 1976, April 1980 and December 1987, diurnal tidal oscillations of winds and temperatures in the 20-80 km height region are studied. The vertical profiles of tidal components obtained from these observations are compared with the theoretically obtained tidal fields. In general, there is agreement between the observational and theoretical profiles, especially in August 1976 and April 1980. However, there are significant differences between the two in certain height ranges.

Journal ArticleDOI
TL;DR: In this paper, the authors reported the trapping of partial disorder in the drop-tube processed Ni[sub 3]Al droplets as large as 400 [mu]m, where the order-disorder ([gamma][prime]-[gamma]) transformation temperature is near the melting temperature.
Abstract: As the highly ordered structure is primarily responsible for the room-temperature brittleness in Ni[sub 3]Al, recent experimental efforts have been addressed to the trapping of disorder during solidification of this intermetallic compound. In their kinetic model for complete disorder trapping, Boettinger and Aziz have predicted the formation of a metastable disordered phase beyond a critical value of the solidification velocity. However, as the order-disorder ([gamma][prime]-[gamma]) transformation temperature, T[sub c], in Ni[sub 3]Al is near the melting temperature, T[sub m] it is very difficult to entrap disorder during solidification of Ni[sub 3]Al. Here the authors report the trapping of partial disorder in the drop-tube processed Ni[sub 3]Al droplets as large as 400 [mu]m.

Journal ArticleDOI
TL;DR: In this paper, a two-body inverse square force model and an inverse square variation of solar pressure with heliocentric distance were employed for minimum time rendezvous transfer of a sail-spacecraft between helispecific, inclined, elliptic orbits.

Journal ArticleDOI
TL;DR: In this paper, a polyimide film based on pyromellitic dianhydride and bis(4-aminophenyl)ether is modified through the incorporation of polymeric copper phtalocyanine containing peripheral carboxyl groups.
Abstract: A polyimide film based on pyromellitic dianhydride and bis(4-aminophenyl)ether is modified through the incorporation of polymeric copper phtalocyanine containing peripheral carboxyl groups. The thermal stability and electric properties of the virgin and modified films and the effect of heat treatment of the films on the electrical properties are investigated.

Journal ArticleDOI
TL;DR: In this paper, copolymers of acrylonitrile with methacrylic acid were synthesized electrochemically and the reaction system consisted of dimethyl formamide as solvent and various quarternary ammonium salts as supporting electrolytes.