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Institution

National Aerospace Laboratories

FacilityBengaluru, India
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.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the correlation between the crystal structure and thermoelectric properties of transition-metal oxides is discussed, including the crystal-site-dependent electronic configuration and spin degeneracy to control the thermopower and electron-phonon interaction.
Abstract: Recent demand for thermoelectric materials for power harvesting from automobile and industrial waste heat requires oxide materials because of their potential advantages over intermetallic alloys in terms of chemical and thermal stability at high temperatures. Achievement of thermoelectric figure of merit equivalent to unity (ZT ≈ 1) for transition-metal oxides necessitates a second look at the fundamental theory on the basis of the structure–property relationship giving rise to electron correlation accompanied by spin fluctuation. Promising transition-metal oxides based on wide-bandgap semiconductors, perovskite and layered oxides have been studied as potential candidate n- and p-type materials. This paper reviews the correlation between the crystal structure and thermoelectric properties of transition-metal oxides. The crystal-site-dependent electronic configuration and spin degeneracy to control the thermopower and electron–phonon interaction leading to polaron hopping to control electrical conductivity is discussed. Crystal structure tailoring leading to phonon scattering at interfaces and nanograin domains to achieve low thermal conductivity is also highlighted.

73 citations

Journal ArticleDOI
TL;DR: In this article, an asymmetric bipolar-pulsed DC power supply and a dc power supply were used to sputter Si and Ti targets, respectively in a reactive direct current (DC) unbalanced magnetron sputtering.
Abstract: Approximately 1.5-amp;mu;m-thick superhard nanocomposite coatings of TiN/Silt;subgt;3lt;/subgt;Nlt;subgt;4lt;/subgt; with varying silicon contents were deposited on silicon and stainless steel (SS 304) substrates by reactive direct current (DC) unbalanced magnetron sputtering. An asymmetric bipolar-pulsed DC power supply and a DC power supply were used to sputter Si and Ti targets, respectively in Ar+Nlt;subgt;2lt;/subgt; plasma. Structural characterization of the coatings was done using X-ray diffraction (XRD). The bonding structure of the nanocomposite coatings was characterized by X-ray photoelectron spectroscopy (XPS). The elemental composition of the TiN/Silt;subgt;3lt;/subgt;Nlt;subgt;4lt;/subgt; nanocomposite coatings was determined using energy dispersive X-ray analysis. The mechanical properties of the coatings were measured using a nanoindentation hardness tester. The surface morphology of the coatings was studied using atomic force microscopy. The nanocomposite coatings exhibited a broad (200) reflection of cubic TiN phase in the XRD data. There was a significant broadening of the (200) reflection with an increase in the silicon content in the nanocomposite coatings, which suggested a decrease in the average crystallite size. Nanoindentation data showed that about 1.5-amp;mu;m-thick TiN/Silt;subgt;3lt;/subgt;Nlt;subgt;4lt;/subgt; nanocomposite coatings exhibited a maximum hardness of 5200 kg/mmlt;supgt;2lt;/supgt; and an elastic modulus of 340 GPa at a silicon concentration of approximately 12 at.%. The hardness and the elastic modulus of the nanocomposite coatings decreased with further increase in the silicon content. Structural changes as a result of heating (400-850 amp;deg;C) of the nanocomposite coatings in air were characterized using micro-Raman spectroscopy. The Raman data showed that the nanocomposite coatings started to oxidize at 800 amp;deg;C as compared to TiN, which have been oxidized even at 500 amp;deg;C. To isolate the oxidation-induced spectral changes as a result of heating of the coatings in air, the samples were also annealed in vacuum at 850 amp;deg;C under similar conditions. The Raman data of the vacuum-annealed coatings showed no phase transformation even after annealing up to 850 amp;deg;C. The corrosion behaviors of single-phase TiN and TiN/Silt;subgt;3lt;/subgt;Nlt;subgt;4lt;/subgt; nanocomposite coatings deposited on stainless steel substrates were investigated using potentiodynamic polarization in 3.5% NaCl solution. The results indicated that the nanocomposite coatings exhibited superior corrosion resistance as compared to the uncoated substrate. The wear data showed that the nanocomposite coatings also exhibited better wear resistance as compared to the uncoated substrate.

73 citations

Journal ArticleDOI
TL;DR: In this paper, the structure and properties of electrodeposited nickel composites reinforced with inert particles like SiC, Si3N4 and Al2O3 was compared with respect to structure, morphology, microhardness and tribological behaviour.

73 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of strain rate on tensile and energy absorbing properties of superelastic NiTi thin wires was investigated and an understanding of the interplay of the ductile behavior, temperature and strain rate effects, energy storage and cycling was gained.
Abstract: This study deals with the effect of strain rate on tensile and energy absorbing properties of superelastic NiTi thin wires. It also attempts to gain an understanding of the interplay of the ductile behavior, temperature and strain rate effects, energy storage and cycling. The wires are in austenite condition at room temperature and above. The strain rates imposed during testing range from 0.2 to 180%/min (i.e., 0.06x2013;54 mm/min) corresponding to a frequency of 2.77 xD7; 10x2212;4 to 0.25 Hz for strain amplitudes of 6%. The corresponding frequency for 8% strain amplitude is 2.08 xD7; 10x2212;4 to 0.18 Hz. It is shown that NiTi SMAs exhibit ductility at both low and high strain rates. This is also true for the cold worked and heat treated conditions both below Mf and above Af. During tensile testing the stress-induced martensite (SIM) plateau increases in length and translates upwards with increase in strain rate up to a certain value. Similarly, the onset of elastic yield stress also increases with strain rate. At high strain rates the SIM segment and elastically deformed SIM segment overlap. The SIM formation is not able to cope with the externally imposed higher strain rates. This is also the reason for the reduction of hysteresis loop at the high strain rates as observed in the cyclic tests.13; The dissipated strain energy density (Ed) increases with increasing strain rate up to a certain value beyond which the Ed decreases. It is clear that the mean point of the superelastic loop shifts to the right and upwards (higher stress and higher strain region) for cyclic testing with increase in strain rates. However, it shifts to the right and downwards (lower stress/higher strain regime) for both the 6 and 8% strain amplitude cycling at constant strain rate. The stabilization of residual strain and Ed is based on the same underlying mechanism relating to SIM formation and occurs at the same numbers of cycles.

73 citations

Proceedings ArticleDOI
03 Dec 2010
TL;DR: This work addresses the inverse kinematics problem for the 7 Degrees of Freedom Barrett Whole Arm Manipulator with link offsets with a parametric solution for all possible geometric poses for a desired end-effector pose.
Abstract: This work addresses the inverse kinematics problem for the 7 Degrees of Freedom Barrett Whole Arm Manipulator with link offsets. The presence of link offsets gives rise to the possibility of the in-elbow & out-elbow poses for a given end-effector pose and is discussed in the paper. A parametric solution for all possible geometric poses is generated for a desired end-effector pose (position and orientation). The set of possible geometric poses are completely defined by three circles in the Cartesian space. A method of computing the joint-variables for any geometric pose is presented. An analytical method of identifying a set of feasible poses for some joint-angle constraints is also addressed.

73 citations


Authors

Showing all 1850 results

NameH-indexPapersCitations
Harish C. Barshilia462366825
K.S. Rajam42834765
Kozo Fujii394115845
Parthasarathi Bera391365329
R.P.S. Chakradhar361664423
T. N. Guru Row363095186
Takashi Ishikawa361545019
Henk A. P. Blom341685992
S. Ranganathan332115660
S.T. Aruna331014954
Arun M. Umarji332073582
Vinod K. Gaur33924003
Keisuke Asai313503914
K. J. Vinoy302403423
Gangan Prathap302413466
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
202310
202216
2021143
2020100
201996
2018119