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.

Tape Casting and Dielectric Properties of Sr2ZnSi2O7‐Based Ceramic–Glass Composite for Low‐Temperature Co‐fired Ceramics Applications

Abstract: The Sr2ZnSi2O7 ceramics sintered at 1475°C has ɛr=85, Qu×f=105,000 GHz (at 1263 GHz), and τf=−515 ppm/°C The sintering temperature of Sr2ZnSi2O7 has been lowered to 875°C by the addition of 20Li2O–20MgO–20ZnO–20B2O3–20SiO2 (LMZBS) glass Addition of a small amount of SrTiO3 lowered the value of τf Tapes were cast using the composition Sr2ZnSi2O7+15 wt% LMZBS The stacked and sintered tapes exhibited ɛr∼7 and tan δ∼10−3 at 290 K The chemical compatibility of Ag with the ceramic–glass composites was also investigated

Stochastic finite element analysis of layered composite beams with spatially varying non-Gaussian inhomogeneities

Abstract: This study focuses on the development of a stochastic finite element-based methodology for failure assessment of composite beams with spatially varying non-Gaussian distributed inhomogeneities. The material properties in the individual laminae are modeled as non-Gaussian random fields, whose probability density functions and the correlations are estimated from the test data. The non-Gaussian random fields are discretized into a vector of correlated non-Gaussian random variables using the optimal linear expansion scheme that preserves the second-order non-Gaussian characteristics of the fields. Subsequently, the estimates of the failure probability are obtained from Monte Carlo simulations carried out on the vector of correlated random variables. Issues related to the computational efficiency of the proposed framework and the variabilities in the material properties are discussed. Numerical examples are presented, which highlight the salient features of the proposed method.

Synthesis, structure and tunable shape memory properties of polytriazoles: dual-trigger temperature and repeatable shape recovery

Abstract: Thermally induced shape memory polymers (SMPs) are capable of storage, release of energy and shape recovery on the macro-scale. In this work, cross-linked SMPs were synthesized from the monomers tris(4-(1-azido 3-oxy propan-2-ol)phenyl) methane (A3), and 1,4-bis(propargyloxy) benzene (B2), and the propargyl functionalized novolac oligomer (B3). The A3B2 polymer exhibited a low trigger temperature of 92 °C, whereas A3B3 registered a higher trigger temperature of 125° C. The extent of shape recovery of both the SMPs was above 95% and it was repeatable for at least 10 times. On repeating the shape memory cycles, the response time for shape recovery increased, but nearly a complete shape recovery was observed in both polymers. In addition, a polymer with dual trigger temperature (83 and 113 °C) was synthesized by click polymerization between the A3 monomer and stoichiometric equivalence of B2 and B3 monomers. The polytriazole networks bearing monophenyl and oligomer structures in tandem enabled both low and high trigger temperature in a single polymeric structure. The SMP possesses a shape recovery to an extent as high as 98% at both the trigger points even on the 10th shape memory cycle. These polymers exhibited hydrophobicity with a static water contact angle of about 90° and very low water absorption ( 230 °C) and are suitable for actuator applications.

Analytical Approach Using KS Elements to Near-Earth Orbit Predictions Including Drag

Abstract: A new analytical theory for the motion of near-Earth satellite orbits with the air drag effect is developed in terms of the KS elements, utilizing an analytical oblate exponential atmospheric density model. Due to the symmetry of the KS element equations, only one of the eight equations is integrated analytically to obtain the state vector at the end of each revolution. This is a uniqueness of the present theory. The series expansions include up to quadratic terms in e (eccentricity) and c (a small parameter dependent on the flattening of the atmosphere). Numerical studies are done with six test cases, selected to cover a wide range of eccentricity and semi-major axis, and a comparison of the three orbital parameters: semi-major axis, eccentricity and argument of perigee perturbed by the air drag with oblate atmosphere is made up to 100 revolutions with the numerically integrated values. The comparison is quite satisfactory. After 100 revolutions, with a ballistic coefficient of 50, a maximum difference of 39 metres is found in the semi-major axis comparison for a very small eccentricity (0.001) case having an initial perigee height of 391.425 km. One important advantage of the present theory is that it is singularity free, a problem faced by the analytical theories developed from the Lagrange's planetary equations. Another advantage is that the state vector is known after each revolution.

Study of damage mechanisms and failure analysis of sintered and hardened steels under rolling–sliding contact conditions

Abstract: Due to continual improvements of the powder material processing, it is possible for powder metal alloys to compete even in some of the most demanding applications. The main lure of powder metallurgy (PM) components amongst the several challenging mass production methods plays an imperative role, as saving material, energy and also provides good fatigue properties, which are equally good and substitute for the conventional methods. The investigation on the lubricated rolling–sliding contact fatigue damage mechanisms in sintered and hardened steel (FLC 4608-110HT) containing combination of closed and interconnected pores has been carried out. Rolling–sliding contact conditions are simulated in twin disc type experimental set up for various contact pressure and slide/roll ratio. The damaged surface of sintered and hardened steel is examined under image analyzer for different sliding conditions. It is observed that the peel of material and surface crack opening is seen for the higher slide/roll ratio. Wear debris analysis is also carried out by dual-ferrograph analyzer for sintered and wrought steels for comparison study. The characteristics of wear morphology and the size, shape and concentration of worn particles are also analysed for different sliding contact conditions.