National Aerospace Laboratories

About: National Aerospace Laboratories is a facility organization based out in Bengaluru, India. It is known for research contribution in the topics: Coating & Corrosion. The organization has 1838 authors who have published 2349 publications receiving 36888 citations.

Investigations on the mechanical behaviour of rough surfaces of TiNi thin films by nano indentation studies

Abstract: Nano hardness tests were conducted on TiNi thin films deposited by sputtering of a mosaic target comprising of segments of Titanium and Nickel. The composition of the films was determined by alpha particle back scattering (RBS). Surface topography of the films, imaged using an AFM, revealed high surface roughness, comparable to the indentation depth, leading to a large scatter and erroneous results from the indentation data. The objectives of the present investigation were (i) to extract the actual hardness of the film from the nano indentation data and (ii) to analyse the contact mechanisms during penetration of the indenter into the film by applying a statistical model of the surface roughness. Various mechanical parameters pertaining to the indentation process, namely, the point of first yield and the plasticity index of the film after deformation have been calculated. Variation of the deformation behaviour of the films as the asperity sizes increase is also reported.

Cryogenic pressure sensitive fluorescent paint systems

Abstract: In recent experiments, we demonstrated the feasibility of using luminescent coatings for surface pressure measurement in a cryogenic wind tunnel. Numerous PSP samples were calibrated and a new coating technology in which luminescent molecules are directly deposited onto an anodized aluminum model surface was developed. The resulting coating has an extremely high oxygen sensitivity for mole fractions of oxygen less than 0.1%. Cryogenic pressure calibration techniques are discussed and calibration curves presented. To demonstrate this technology, a 14%thick bump model was tested in the 0.1-m Transonic Cryogenic Wind Tunnel at NAL. Mach number was changed from 0.4 to 0.84 whereas temperature was maintained at 100 K. A small amount of oxygen was injected into the tunnel and the mole fraction of oxygen ( 250 PPM )in the test gas was kept constant. The results using an in situ calibration for the paintderived pressure distributions are in good agreement with pressure tap measurements.

The no-slip boundary condition in fluid mechanics

Abstract: A moving fluid in contact with a solid body cannot have velocity relative to the body. Even though the question whether there is slip has been satisfactorily resolved now, it was a difficult and controversial problem. In the first part of this article several basic ideas and details related to this problem are discussed. The concluding part of the article will trace the development of ideas leading to the resolution of this important question. Extreme cases where fluid does slip will also be discussed.