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.

Studies on Al–Cu–Li–Mg–Ag–Zr alloy processed through vacuum induction melting (VIM) technique

Abstract: A new technique of lithium addition has been adapted for the processing of Al–Cu–Li–Ag–Mg–Zr alloy, which gives more than 90% recovery of lithium throughout the billet. Processing studies on this alloy include casting, three step homogenization, to avoid incipient melting, and mechanical working particularly forging and rolling. The products in the form of sheets were subjected to various T6 (solution treatment + water quenching + aging) tempers. Mechanical properties were evaluated at room temperature and correlated with microstructure. Characterizations using optical microscope and post-fracture analysis have been carried out using Scanning electron microscope (SEM). Experimental investigation shows highest mechanical properties for the Al–1.3%Li alloy in T6 (500 °C/1 h + WQ + 190 °C/24 h) condition.

Strengthening mechanisms in CrMoNbTiW refractory high entropy alloy

Abstract: We have investigated the strengthening mechanisms of as-cast CrMoNbTiW BCC refractory high entropy alloy (RHEA). The cast RHEA was deformed at a constant strain rate of 10−3 s−1 and a temperature range of 1100–1300 °C. The various factors contributing to the overall strength of the cast alloy are explored with comprehensive experimental evidence. In as-cast RHEA, solid solution strengthening is the dominant mechanism among other factors. A modified Varvenne's solid solution strengthening model is used to predict the yield strength (YS) of the RHEA at high temperatures. The experimentally determined YS exhibits a strong temperature dependence, and the predicted YS values are significantly affected by the temperature-dependent material constants. The absolute value of the predicted YS depends on the shear modulus, whereas the variation of YS with temperature is affected by the Poisson's ratio. Moreover, our study demonstrates that it is feasible to predict the high temperature YS using material constants from literature besides DFT studies.

Oxygen emission lines in the high resolution spectra of 9P/Tempel 1 following the Deep Impact event

Abstract: Context. On 2005 July 4, the NASA spacecraft Deep Impact delivered an impactor on the comet 9P/Tempel 1 to study the material ejected from the nucleus. A worldwide observation campaign accompanied the mission, to characterize the activity of 9P/Tempel 1 before and after the impact. Aims. At La Palma (Canary Islands), the comet was observed from July 2 to July 9 using the echelle spectrograph SARG on the Telescopio Nazionale Galileo (TNG). Fifteen spectra were obtained with a resolving power of R = 29 000 in the spectral range 4620–7920 A. Many interesting emission lines can be found in this range, in particular the [OI] lines at 5577 A (“green line”) and at 6300 and 6364 A (“red doublet ”). From the analysis of these lines it is possible to derive information on the processes that produce these emissions. Methods. The three atomic oxygen lines are clearly visible in most of the spectra. The intensity ratio between the green line and the sum of the red lines, indicative of the parent of these lines, was computed for 9 of the 15 spectra. The value of the intensity ratio for the night of July 5 was compared with the model results obtained from a coupled chemistry transport model. Results. The intensity ratio of green to red oxygen lines obtained from the observed spectra and the one derived from the model suggest water is the main parent of the [OI] emissions on comet 9P/Tempel 1. Conclusions.