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.

Corrosion and nanomechanical behaviors of plasma electrolytic oxidation coated AA7020-T6 aluminum alloy

Abstract: Alumina coating was deposited on AA7020 aluminum alloy by plasma electrolytic oxidation (PEO) method. The corrosion, stress corrosion cracking (SCC) and nano-mechanical behaviors were examined by means of potentiodynamic polarization, slow strain rate test (SSRT) and nano-indentation tests. Potentiodynamic polarization (PP) was used to evaluate the corrosion resistance of the coating and slow strain rate test (SSRT) was used for evaluating the environmental cracking resistance in 3.5% NaCl solution. The mechanical properties (hardness and elastic modulus) were obtained from each indentation as a function of the penetration depth across the coating cross section. The above results were compared with similar PEO coated aluminum and magnesium alloys. Results indicated that PEO coating on AA7020 alloy significantly improved the corrosion resistance. However the environmental cracking resistance was found to be only marginal. The hardness and elastic modulus values were found to be much higher when compared to the base metal and similar PEO coated 7075 aluminum alloys. The fabricated coating also exhibited good adhesive strength with the substrate similar to other PEO coated aluminum alloys reported in the literature

Fine and ultrafine particles at a near–free tropospheric environment over the high‐altitude station Hanle in the Trans‐Himalaya: New particle formation and size distribution

Abstract: [1] Number-size distributions of ultrafine, fine, and accumulation mode aerosols in the size range 5–1300 nm have been measured regularly from the pristine, high-altitude (for 4520 m above mean sea level) station Hanle in the Trans-Himalaya during the summer and autumn (August–November) 2009. The total number concentration ranged from 80 to 8000 cm−3 with a mean value of 1150 cm−3. Examination of the temporal variations of the size distributions indicated that formation of new ultrafine particles from the precursor gases (probably transported from the valley regions) was highly probable during the forenoon hours of the day, especially during the summer when the insolation was abundant, the process becoming increasingly less efficient as the season progressed toward winter. The time of occurrence of maximum concentration was generally during the forenoon, a few hours after sunrise, and this time shifted to later parts of the day as the season progressed toward winter, probably associated with later sunrise and low solar elevations. The number-size distributions revealed two prominent modes: a nucleation mode with mode diameter at ∼16 nm and a consistent accumulation mode with the mode diameter ranging between 115 and 150 nm. Examining the temporal features with the air mass types, it was noticed that the number concentration increased, and the accumulation mode broadened when west Asian air mass prevailed. In summer (during August) the number concentrations tended to higher values associated with air mass from the Indian origin. The ratio of the Aitken to accumulation mode concentration indicated that the aerosol particles existing over the site are aged.

Effect of pre- and post-weld heat treatments on the mechanical properties of electron beam welded Ti-6Al-4V alloy

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.