Vikram Sarabhai Space Centre

About: Vikram Sarabhai Space Centre is a facility organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Aerosol & Ultimate tensile strength. The organization has 2092 authors who have published 3058 publications receiving 47975 citations. The organization is also known as: VSSC.

Reactive Alder‐ene blend of diallyl bisphenol A novolac and bisphenol A bismaleimide: synthesis, cure and adhesion studies

Abstract: A novel, addition-curable novolac resin (ABPF) was synthesized by the reaction of diallyl bisphenol A with formaldehyde using p-toluene sulfonic acid as the catalyst. The synthesis conditions were optimized to obtain soluble polymer of desirable molecular weight distribution which was characterized by FT-IR, NMR and SEC. ABPF was reactively blended with bisphenol A bismaleimide (BMIP) and cured through an Alder-ene reaction at high temperatures. The cure characteristics of BMIP–ABPF blend with a maleimide:allyl phenol stoichiometry of 1:1 were studied using FT-IR, DSC and DMA, which evidenced the multi-step cure reactions taking place in the system. Cure optimization was evaluated by DSC, DMA and adhesive property tests. The moderately crosslinked blend was conducive for achieving the optimum adhesive properties on aluminium substrates. Retention of the adhesive properties was greater than 100% at 150 °C. © 2001 Society of Chemical Industry

Kinetic energy distributions and line profile measurements of dissociation products of water upon electron impact

Abstract: [1] The Doppler line profiles of H Ly-α (1216 A) and O I (1302 A and 1152 A) resulting from electron impact dissociative excitation of H2O have been measured with a high-resolution (λ/Δλ = 50,000) ultraviolet spectrometer. The line profiles are used to calculate the kinetic energy distribution of the hydrogen atoms produced in dissociative excitation and ionization of H2O at electron impact energies 25, 35, and 100 eV. Three distinct populations of H(2p) atoms were found. The kinetic energy of hydrogen atoms is found to have contributions from a low-energy component, with a mean energy of ∼0.2 eV at all the three electron impact energies. In addition, a medium-energy component appears with a mean energy of ∼2.0 eV for 35 eV electrons, and a high-energy component, ∼7 eV, for 100 eV electrons. The measurement of O I (1302 A) and O I (1152 A) line profiles indicate that the kinetic energy of excited O I atoms is very small (∼1 eV or less) at all electron impact energies. Most of the energy released in dissociation is found in the translational energy of the hydrogen atoms. The excitation functions of H Ly-α, O I (1302 A) feature of oxygen, and A(0) − X(0) molecular band of hydroxyl near 3050 A from threshold to 600 V were also measured. The spectrum (1.0 A FWHM) of the rotational structure of OH (A − X) from electron impact dissociation indicates a high degree of rotational excitation, which is almost identical to the rotational structure from dissociative recombination of H2O+. The results presented in this paper have important applications to planetary bodies, like comets, icy satellites of outer planets, Saturn's magnetosphere, and rings, all of which have H2O and its daughter products in large amount.

Strain hardening of Titanium alloy Ti6Al4V sheets with prior heat treatment and cold working

Abstract: Strain hardening of Titanium alloy Ti6Al4V has been studied at four different strain rates (10 −4 to 10 −1 s −1 ) under tensile loading at four different heat treatment conditions viz. mill annealing (MA), recrystallization annealing (RA), solution treatment (ST) and solution treatment and aging (STA). Effect of prior cold working before tensile testing has also been studied. Strain hardening exponent (n) is found to be decreasing with increasing strain rates for samples in all the four heat treatment conditions, whereas trend is found to be opposite in case, of cold worked (~15%) samples prior to tensile testing. This is due to rearrangement of dislocations generated during the prior cold working. Strength coefficient (K) is also found to follow similar trend. Optical microstructure clearly showed two phase (α+β) structure in all the samples and completely fragmented grain boundaries in cold worked condition. Non-basal oriented grains in as-annealed samples and higher volume fraction of basal (0001) grains in annealed and cold worked samples were observed along with fragmented grain boundaries/regions of void coalescence. Low angle misorientation was found to be lower in sample subjected to STA heat treatment as compared to other heat treated conditions. Twinning was observed in ST as well as in STA conditions, which was absent in annealed as well as annealed and cold worked samples. Image quality maps revealed regions of low image quality in deformed samples indicating presence of high dislocation density. Regions of void coalescence were confirmed by KAM (Kernel average misorientation) maps, GOS (grain orientation spread) maps and unique grain colour maps. Analysis of fractographs showed ductile mode of fracture in all heat treated conditions and mixed mode of fracture with fragmented grain boundaries in all samples subjected to heat treatment followed by tensile testing with prior cold working.