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Sutrakar V.K.,Aeronautical Development Establishment | Sutrakar V.K.,Indian Institute of Science | Sutrakar V.K.,Aeronautical Development Agency | Roy Mahapatra D.,Indian Institute of Science
Journal of Nanoparticle Research | Year: 2011

A novel size dependent FCC (face-centered-cubic) → HCP (hexagonally-closed-pack) phase transformation and stability of an initial FCC zirconium nanowire are studied. FCC zirconium nanowires with cross-sectional dimensions <20 Å are found unstable in nature, and they undergo a FCC → HCP phase transformation, which is driven by tensile surface stress induced high internal compressive stresses. FCC nanowire with cross-sectional dimensions >20 Å, in which surface stresses are not enough to drive the phase transformation, show meta-stability. In such a case, an external kinetic energy in the form of thermal heating is required to overcome the energy barrier and achieve FCC → HCP phase transformation. The FCC-HCP transition pathway is also studied using Nudged Elastic Band (NEB) method, to further confirm the size dependent stability/metastability of Zr nanowires. We also show size dependent critical temperature, which is required for complete phase transformation of a metastable-FCC nanowire. © 2011 Springer Science+Business Media B.V.

Sutrakar V.K.,Aeronautical Development Establishment | Sutrakar V.K.,Aeronautical Development Agency
Journal of Physics Condensed Matter | Year: 2014

In this paper, atomistic modeling of L10-TiAl nanowire has been performed utilizing the Embedded Atom Method (EAM) potential under strain-controlled cyclic loading. A nanowire oriented along the <100> axis with a cross-sectional dimension (D) of ∼80 Å with a Length-to-width (L/D) ratio of 10.0 has been considered. Strain-controlled cyclic loading at room temperature has been performed by oscillating the nanowire length dimension sinusoidal with a specific amplitude and period. Tension-compression cyclic loading was employed with zero mean strain. Cyclic loading with percentage strains (%ε) of one to five percent have been considered. It has been observed that the cyclic stress in the nanowire continues to fluctuate during the initial loading cycles. However, once the nanowire becomes stable, a smooth variation of stresses with varying strain has been observed. The cause of initial fluctuations in the nanowire has been studied by varying (a) the amount of load (strain) applied, (b) the nanowire structure during cyclic loading, and (c) the rate at which the load has been applied. It has been identified that the rate of loading could be used for controlling the initial fluctuations of nanowire. Finally, a method for the calculation of cyclic stress versus cyclic strain for nanowires has been proposed. A cyclic stress versus cyclic strain curve has been plotted for a given L/D = 10 and a period of 10 ps. Results show that the TiAl nanowire is having 3/2 times higher stiffness in tension as compared to compression at a given strain under cyclic loading. © 2014 IOP Publishing Ltd.

Siengchin S.,King Mongkut's University of Technology Bangkok | Abraham T.N.,Aeronautical Development Establishment
Journal of Applied Polymer Science | Year: 2013

The polyolefin blends of high-density polyethylene (HDPE) with two types of fluorothermoplastics (THV500 and THV220); were prepared by melt compounding technique. The morphology, crystallization, and the viscoelastic measurements of the blends were carried out. The dispersion of THVs was studied by scanning electron microscopy (SEM) technique, and discussed. The crystallization characteristics of the blend were studied using Differential scanning calorimetry (DSC). The oscillatory shear measurement was employed for determining the rheological properties of the prepared blends. There is a significant difference in the rheological behavior of the HDPE blends with THV500 and THV220. The dynamic linear viscoelastic behavior (storage modulus and viscosity) of HDPE/THV500 was found to be higher than that of HDPE/THV220 blend. This was attributed to the molecular weight and particle size distribution of THVs. However, the molecular weight effect of THVs on the crystallization behavior of the blend is marginal. The master curves of the storage and loss modulus vs. frequency were constructed by applying the time-temperature-superposition (TTS) principle. It was established that the parsimonious and modified Cox-Merz models are fairly applicable to the storage modulus and viscosity results. Copyright © 2012 Wiley Periodicals, Inc.

Sutrakar V.K.,Aeronautical Development Establishment | Sutrakar V.K.,Indian Institute of Science | Mahapatra D.R.,Indian Institute of Science
Materials Letters | Year: 2010

A novel superplastic deformation in an intermetallic B2-NiAl nanowire of cross-sectional dimensions of ∼ 20 Å with failure strain as high as ∼ 700% at 700 K temperature is reported. The minimum temperature under which the superplasticity has been observed is around 0.36 Tm, which is much lower than 0.5 Tm (Tm = melting temperature i.e. 1911 K for bulk B2-NiAl). Superplasticity is observed due to transformation from crystalline phase to amorphous phase after yielding of the nanowire. © 2010 Elsevier B.V. All rights reserved.

Sutrakar V.K.,Aeronautical Development Establishment | Sutrakar V.K.,Indian Institute of Science | Mahapatra D.R.,Indian Institute of Science
Intermetallics | Year: 2010

A novel stress induced martenistic phase transformation is reported in an initial B2-CuZr nanowire of cross-sectional dimensions in the range of 19.44 × 19.44-38.88 × 38.88 Å 2 and temperature in the range of 10-400 K under both tensile and compressive loading. Extensive Molecular Dynamic simulations are performed using an inter-atomic potential of type Finnis and Sinclair. The nanowire shows a phase transformation from an initial B2 phase to BCT (body-centered-tetragonal) phase with failure strain of ∼40% in tension, whereas in compression, comparatively a small B2 → BCT phase transformation is observed with failure strain of ∼25%. Size and temperature dependent deformation mechanisms which control ultimately the B2 → BCT phase transformation are found to be completely different for tensile and compressive loadings. Under tensile loading, small cross-sectional nanowire shows a single step phase transformation, i.e. B2 → BCT via twinning along {100} plane, whereas nanowires with larger cross-sectional area show a two step phase transformation, i.e. B2 → R phase → BCT along with intermediate hardening. In the first step, nanowire shows phase transformation from B2 → R phase via twinning along {100} plane, afterwards the nanowire deforms via twinning along {110} plane which cause further transformation from R phase → BCT phase. Under compressive loading, the nanowire shows crushing along {100} plane after a single step phase transformation from B2 → BCT. Proper tailoring of such size and temperature dependent phase transformation can be useful in designing nanowire for high strength applications with corrosion and fatigue resistance. © 2009 Elsevier Ltd. All rights reserved.

Sutrakar V.K.,Aeronautical Development Establishment | Sutrakar V.K.,Indian Institute of Science | Roy Mahapatra D.,Indian Institute of Science
Journal of Physical Chemistry C | Year: 2011

Atomistic simulation of Ag, Al, Au, Cu, Ni, Pd, and Pt FCC metallic nanowires show a universal FCC → HCP phase transformation below a critical cross-sectional size, which is reported for the first time in this paper. The newly observed HCP structure is also confirmed from previous experimental results. Above the critical cross-sectional size, initial 〉100〈/{100} FCC metallic nanowires are found to be metastable. External thermal heating shows the transformation of metastable 〉100〈/{100} FCC nanowires into 〉110〈/{111} stable configuration. Size dependent metastability/ instability is also correlated with initial residual stresses of the nanowire by use of molecular static simulation using the conjugant gradient method at a temperature of 0 K. It is found that a smaller cross-sectional dimension of an initial FCC nanowire shows instability due to higher initial residual stresses, and the nanowire is transformed into the novel HCP structure. The initial residual stress shows reduction with an increase in the cross-sectional size of the nanowires. A size dependent critical temperature is also reported for metastable FCC nanowires using molecular dynamic, to capture the 〉110〈/{111} to 〉100〈/{100} shape memory and pseudoelasticity. © 2011 American Chemical Society.

Sutrakar V.K.,Aeronautical Development Establishment | Sutrakar V.K.,Indian Institute of Science | Roy Mahapatra D.,Indian Institute of Science
Intermetallics | Year: 2010

The asymmetric stress-strain behavior under tension/compression in an initial 〈100〉 B2-NiAl nanowire is investigated considering two different surface configurations i.e., 〈100〉/(0 1 0) (0 0 1) and 〈100〉/(0 1 1) (0 -1 1). This behavior is attributed to two different deformation mechanisms namely a slip dominated deformation under compression and a known twinning dominated deformation under tension. It is also shown that B2 → BCT (body-centered-tetragonal) phase transformation under tensile loading is independent of the surface configurations for an initial 〈100〉 oriented NiAl nanowire. Under tensile loading, the nanowire undergoes a stress-induced martensitic phase transformation from an initial B2 phase to BCT phase via twinning along {110} plane with failure strain of ∼0.30. On the other hand, a compressive loading causes failure of these nanowires via brittle fracture after compressive yielding, with a maximum failure strain of ∼-0.12. Such brittle fracture under compressive loading occurs via slip along {110} plane without any phase transformations. Softening/hardening behavior is also reported for the first time in these nanowires under tensile/compressive loadings, which cause asymmetry in their yield strength behavior in the stress-strain space. Result shows that a sharp increase in energy with increasing strain under compressive loading causes hardening of the nanowire, and hence, gives improved yield strength as compared to tensile loading. © 2010 Elsevier Ltd. All rights reserved.

Ratna D.,Naval Materials Research Laboratory | Jagtap S.B.,Naval Materials Research Laboratory | Abraham T.,Aeronautical Development Establishment
Polymer Engineering and Science | Year: 2013

Poly (ethylene oxide) (PEO)/multiwall carbon nanotubes (MWCNT) nanocomposites were prepared by dispersion of MWCNTs in aqueous solution using half neutralized sodium salt of sebacic acid as a modifier. The physical interaction of half neutralized sodium salt of sebacic acid with MWCNT (cation-π interaction) has been established by using Fourier transform infrared and Raman spectroscopic analyses. Such interaction helps in debundling the MWCNTs and resulted in a better dispersion in PEO matrix as confirmed by scanning electron microscopy and transmission electron microscopy. Addition of MWCNT significantly improves the storage modulus in rheological measurements as well as in dynamic mechanical thermal analysis. The crystallization behaviors of the composites made with the unmodified and modified MWCNTs were investigated. The modified MWCNT-based composites shows large number of spherulite with smaller size compared to those observed in unmodified MWCNT-based composite. © 2012 Society of Plastics Engineers.

Sutrakar V.K.,Aeronautical Development Establishment | Sutrakar V.K.,Indian Institute of Science | Roy Mahapatra D.,Indian Institute of Science | Pillai A.C.R.,Aeronautical Development Establishment
Journal of Physics Condensed Matter | Year: 2012

Atomistic simulation of initial 100 oriented FCC Cu nanowires shows a novel coupled temperaturepressure dependent reorientation from 100 to 110 phase. A temperaturepressure-induced solidsolid 100 to 110 reorientation diagram is generated for Cu nanowire with varying cross-sectional sizes. A critical pressure is reported for Cu nanowires with varying cross-sectional sizes, above which an initial 100 oriented nanowire shows temperature independent reorientation into the 110 phase. The effect of surface stresses on the 100 to 110 reorientation is also studied. The results indicate that above a critical cross-sectional size for a given temperaturepressure, 100 to 110 reorientation is not possible. It is also reported here that for a given applied pressure, an increase in temperature is required for the 100 to 110 reorientation with increasing cross-sectional size of the nanowire. The temperaturepressure-induced solidsolid 100 to 110 reorientation diagram reported in the present paper could further be used as guidelines for controlling the reorientations/shape memory in nano-scale applications of FCC metallic nanowires. © 2012 IOP Publishing Ltd.

Ramasamy M.,Aeronautical Development Establishment | Ramasamy M.,Indian Institute of Science | Ghose D.,Indian Institute of Science
2016 International Conference on Unmanned Aircraft Systems, ICUAS 2016 | Year: 2016

In this paper, we present an algorithm called Learning-based Preferential Surveillance Algorithm (LPSA), which is specific to the problem of persistent surveillance by unmanned aerial vehicles. The novelty of the algorithm lies in providing the capability to a UAV to increase the probability of target detection through learning. The algorithm considers the neighborhood of a localized target as potential additional targets and motivates the UAV to verify if this is indeed true. Once a target is located in any of the neighborhood grid points, that point is visited more often than other points. Moreover, this technique uses the risk calculation method of an existing geometric reinforcement learning algorithm to reduce the frequency of visits to risky regions. Simulation results are used to demonstrate the effectiveness of the algorithm. © 2016 IEEE.

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