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.

Experimental and analytical estimates of fatigue crack closure in an aluminium‐copper alloy part ii: a finite element analysis

Abstract: A numerical investigation of the fatigue crack closure phenomenon has been performed by an elastic-plastic finite element analysis. Computer software was developed to consider many aspects affecting plasticity-induced crack closure. Linear and power-law hardening models are considered in the finite element analysis. The paper presents results from the study carried out on compact tension (CT) coupons at various crack lengths corresponding to different loading conditions. Finally the results of the analysis are compared with the experimental estimates of fatigue crack closure levels obtained from laser interferometry, scanning-electron and transmission-electron fractography presented in Part I of this paper on identical specimens.

Coupling remote sensing observation models and a growth model for improved retrieval of (geo)biophysical information from optical remote sensing data

Abstract: In the ESA study GeoBIRD (Geo- and Biophysical Information from Remote Sensing Data) the process-based vegetation growth model PROMET-V was coupled to the GeoSAIL canopy reflectance model for the retrieval of spatially distributed biophysical parameters from surface reflectance images derived from Landsat TM data. The raster based PROMET-V model calculates plant growth, water and nitrogen fluxes using meteorological data, a land use map, and a soil map. In this study the total leaf area index (LAI), the fraction brown leaf area and surface soil moisture, as modelled in PROMET-V, were used in conjunction with GeoSAIL, to model the surface reflectance spectra. Besides modelling the canopy reflectance GeoSAIL, also accounts for the soil reflectance using the dry soil spectrum and surface moisture as inputs. By minimising the difference between observed reflectance spectra derived from LANDSAT images and the modelled surface reflectance spectra, the total LAI, fraction of brown leaves and surface soil moisture were estimated. This optimisation process is constrained by physically and plant physiologically meaningful boundaries in order to obtain valid results and accelerate the process. By re-initialising the PROMET-V model, the retrieved and simulated LAI were matched. This leads to improved model results regarding biomass and yield.

Wettability of Y2O3: A Relative Analysis of Thermally Oxidized, Reactively Sputtered and Template Assisted Nanostructured Coatings

Abstract: The wettability of reactively sputtered Y2O3, thermally oxidized Y-Y2O3 and Cd-CdO template assisted Y2O3 coatings has been studied. The wettability of as-deposited Y2O3 coatings was determined by contact angle measurements. The water contact angles for reactively sputtered, thermally oxidized and template assisted Y2O3 nanostructured coatings were 99°, 117° and 155°, respectively. The average surface roughness values of reactively sputtered, thermally oxidized and template assisted Y2O3 coatings were determined by using atomic force microscopy and the corresponding values were 3, 11 and 180 nm, respectively. The low contact angle of the sputter deposited Y2O3 and thermally oxidized Y-Y2O3 coatings is attributed to a densely packed nano-grain like microstructure without any void space, leading to low surface roughness. A water droplet on such surfaces is mostly in contact with a solid surface relative to a void space, leading to a hydrophobic surface (low contact angle). Surface roughness is a crucial factor for the fabrication of a superhydrophobic surface. For Y2O3 coatings, the surface roughness was improved by depositing a thin film of Y2O3 on the Cd-CdO template (average roughness = 178 nm), which resulted in a contact angle greater than 150°. The work of adhesion of water was very high for the reactively sputtered Y2O3 (54 mJ/m2) and thermally oxidized Y-Y2O3 coatings (43 mJ/m2) compared to the Cd-CdO template assisted Y2O3 coating (7 mJ/m2).