Showing papers by "National Aerospace Laboratories published in 2020"

Effect of Electrolyte Temperature and Anodization Time on Formation of TiO2 Nanotubes for Biomedical Applications

Abstract: We have investigated the formation of self-organized titanium oxide nanotube layers by anodic oxidation on titanium alloys in electrolyte solutions with different temperatures (5, 10, 25, 30, 50 and 70 °C). Pore diameter and the wall thickness of nanotube arrays were controlled by varying anodization time and temperature. We have observed significant outcomes in the formation of TiO2 nanotube arrays at 25 °C with an average inner pore diameter of 125 nm, length of ∼250 nm, the wall thickness of 30 nm and an inter-tube space 35 nm. Nanotube arrays were smooth and circular without any defect in morphology. In addition, anodization of Commercially Pure Titanium (CP Ti) and titanium alloys (Ti-6Al-4 V, Ti-6Al-7Nb, Ti-13Nb-13Zr, and β-21 s) was carried out at optimized parameter to understand their significance on TiO2 nanotube arrays formation.

Sputter deposited p-NiO/n-SnO2 porous thin film heterojunction based NO2 sensor with high selectivity and fast response

Abstract: In this work, we report fabrication and characterization of porous, single layer n-SnO2, p-NiO and bilayer thin film heterojunction devices developed using pulsed DC magnetron sputtering for NO2 detection. Template-free, NiO/SnO2 heterojunction devices were deposited both in top-bottom and in-plane electrode configurations. All the devices showed an optimum sensing temperature of 200 °C. Systematic comparison of the fabricated devices revealed that the heterojunction devices with top-bottom electrodes improved performance. Electrical characterization confirmed the formation of heterojunction across the interface. The response values of the heterojunction sensor ranged from 57 to 144 % for the NO2 concentration range of 2–10 ppm. The heterojunction device showed high selectivity against CO and NH3 with selectivity coefficients of 90 and 26, respectively. The heterojunction sensor exhibited fast response and recovery times of 37 and 98 s, respectively. The device showed excellent stability with

Fluid Density Sensing Using Piezoelectric Micromachined Ultrasound Transducers

Abstract: We report on the suitability of a Piezoelectric Micromachined Ultrasound Transducer (PMUT) based system for fluid density measurement in both static and dynamic conditions. We exploit the well-known phenomenon of the virtual added mass induced changes in the resonant frequency of a structure vibrating in a fluid medium to design, fabricate and test a unique PMUT-fluid-PMUT (PFP) system as a fluid density sensor. The proposed system uses through-transmission of ultrasound waves from one PMUT transducer to another identical transducer with the test fluid in between and records the shift in the resonant peak of the receiver PMUT. We also study the sensitivity of the system using different sized PMUTs with resonant frequencies ranging from 140 kHz to 1.8 MHz and show how the system can be designed for a desired sensitivity. Further, we carry out experiments with dynamic density changes by mixing fluids to study how the system could be used to track changes in the density of a flowing liquid in real-time. We also study the effect of the distance separating the transmitter and the receiver to establish the utility of the system in both micro and macro scales in static as well as dynamic conditions.

Solid particle erosion and corrosion resistance performance of nanolayered multilayered Ti/TiN and TiAl/TiAlN coatings deposited on Ti6Al4V substrates

Abstract: Solid particle erosion by air born dust particles and corrosion by humid air and sea salt cause severe damage to the gas turbine blades and wind turbines. Combination of erosion and corrosion accelerates the damage process compared to the individual effects. The damage leads to the economic loss, pollution and low safety. In order to protect these components, ultra-thin multilayered erosion and corrosion resistant Ti/TiN and TiAl/TiAlN coatings with stress absorbing layers were developed on Ti6Al4V substrates using un-balanced magnetron sputtering process. Erosion resistance of Ti/TiN and TiAl/TiAlN coatings was tested according to the ASTM-G76-13 standards at four different impinging angles: 90°, 60°, 45° and 30°. Erosion tests were conducted at 400 °C with increasing erodent velocity (30 to 90 m/s) using alumina and silica erodent particles. Average erosion resistance of Ti/TiN and TiAl/TiAlN coatings was significantly higher than Ti6Al4V substrate. Corrosion resistance of the coatings was found to be almost one order better than Ti6Al4V substrate in 3.5% NaCl solution. Morphology and spectroscopic analysis of the erosion scars were studied using field emission scanning electron microscopy and micro-Raman spectroscopy, respectively. Chemical stability of TiAl/TiAlN was found to be better than Ti/TiN in 3.5% NaCl solution.

Interaction of convective organization with monsoon precipitation, atmosphere, surface and sea: The 2016 INCOMPASS field campaign in India

Abstract: The INCOMPASS field campaign combines airborne and ground measurements of the 2016 Indian monsoon, towards the ultimate goal of better predicting monsoon rainfall. The monsoon supplies the majority of water in South Asia, but forecasting from days to the season ahead is limited by large, rapidly developing errors in model parametrizations. The lack of detailed observations prevents thorough understanding of the monsoon circulation and its interaction with the land surface: a process governed by boundary‐layer and convective‐cloud dynamics. INCOMPASS used the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe‐146 aircraft for the first project of this scale in India, to accrue almost 100 h of observations in June and July 2016. Flights from Lucknow in the northern plains sampled the dramatic contrast in surface and boundary‐layer structures between dry desert air in the west and the humid environment over the northern Bay of Bengal. These flights were repeated in pre‐monsoon and monsoon conditions. Flights from a second base at Bengaluru in southern India measured atmospheric contrasts from the Arabian Sea, over the Western Ghats mountains, to the rain shadow of southeast India and the south Bay of Bengal. Flight planning was aided by forecasts from bespoke 4 km convection‐permitting limited‐area models at the Met Office and India's NCMRWF. On the ground, INCOMPASS installed eddy‐covariance flux towers on a range of surface types, to provide detailed measurements of surface fluxes and their modulation by diurnal and seasonal cycles. These data will be used to better quantify the impacts of the atmosphere on the land surface, and vice versa. INCOMPASS also installed ground instrumentation supersites at Kanpur and Bhubaneswar. Here we motivate and describe the INCOMPASS field campaign. We use examples from two flights to illustrate contrasts in atmospheric structure, in particular the retreating mid‐level dry intrusion during the monsoon onset.

Urban Heat Island studies: Current status in India and a comparison with the International studies

Abstract: Urbanization has resulted in many critical issues like increase in pollution levels, sudden climatic changes and the rise of temperature in the urban area, that is the formation of Urban Heat Islands (UHI). As the density of population rises, most of the land areas are being converted into cities and cities grows very rapidly. Due to the UHI effect, the cities are becoming hotter day by day. In India, all the metropolitan cities are victims of UHI effect and the severity of heat formation, necessitates research in this area. The present paper evaluates the trends of UHI studies in Indian cities and its out reach till 2018. Heat Island classification, methods of studying UHI in India and their limitation are discussed. Eventually a comparison of new trends of UHI studies in the world and where India lacks its growth in UHI research are included in this paper. One of the findings is that numerical modelling studies are very limited in India in this field and more focus in this area is required.

Solution combustion synthesis, characterization, magnetic, and dielectric properties of CoFe2O4 and Co0.5M0.5Fe2O4 (M = Mn, Ni, and Zn).

Abstract: Nanocrystalline CoFe2O4 and Co0.5M0.5Fe2O4 (M = Mn, Ni, and Zn) ferrites were prepared by the solution combustion method using oxalyl dihydrazide as a fuel. These materials were characterized by several physicochemical techniques. X-ray diffraction (XRD) patterns indicate the cubic spinel structure of these ferrites. Field emission scanning electron microscopy (FESEM) images demonstrate the microporous nature of the materials because of the large amount of gas production during their synthesis. High resolution transmission electron microscopy (HRTEM) images show lattice fringes corresponding to the {220} and {311} planes of the spinel structure. Fourier transform infrared (FTIR) spectra exhibit absorption bands around the 500-600 cm-1 wavenumber region which are related to metal-oxygen bonds with tetrahedral coordination. Symmetric and asymmetric stretching and symmetric bending modes associated with tetrahedral and octahedral cations present in the spinel structures have been assessed by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) studies demonstrate the presence of Co2+, Mn2+, Ni2+, Zn2+, and Fe3+ in tetrahedral and octahedral coordinations in these ferrites. Co0.5Zn0.5Fe2O4 is observed to show the highest saturation magnetization among all these materials. The dielectric measurements reveal that the dielectric constant and loss values decrease with an increase in frequency and the ac conductivity increases at higher frequencies due to mobilization of the charge carriers.

The dynamic and thermodynamic structure of the monsoon over southern India: New observations from the INCOMPASS IOP

Abstract: Some of the highest summer monsoon rainfall in South Asia falls on the windward slopes of the Western Ghats mountains on India’s west coast and offshore over the eastern Arabian Sea. Understanding of the processes determining the spatial distribution and temporal variability of this region remains incomplete. In this paper, new Interaction of Convective Organization and Monsoon Precipitation, Atmosphere, Surface and Sea (INCOMPASS) aircraft and ground-based measurements of the summer monsoon over the Western Ghats and upstream of them are presented and placed within the context of remote sensing observations and reanalysis. The transition from widespread rainfall over the eastern Arabian Sea to rainfall over the Western Ghats is documented in high spatial and temporal resolution. Heavy rainfall offshore during the campaign was associated primarily with mid-tropospheric humidity, secondarily with sea surface temperature, and only weakly with orographic blocking. A mid-tropospheric dry intrusion suppressed deep convection offshore in the latter half of the campaign, allowing the build-up of low-level humidity in the onshore flow and enhancing rainfall over the mountains. Rainfall on the lee side of the Western Ghats occurred during the latter half of the campaign in association with enhanced mesoscale easterly upslope flow. Diurnal cycles in rainfall offshore (maximum in the morning) and on the mountains (maximum in the afternoon) were observed. Considerable zonal and temporal variability was seen in the offshore boundary layer, suggesting the presence of convective downdrafts and cold pools. Persistent drying of the subcloud mixed layer several hundred kilometres off the coast was observed, suggesting strong mixing between the boundary layer and the free troposphere. These observations provide quantitative targets to test models and suggest hypotheses on the physical mechanisms determining the distribution and variability in rainfall in the Western Ghats region.

Reference-Free Real-Time Power Line Monitoring Using Distributed Anti-Stokes Raman Thermometry for Smart Power Grids

Abstract: We report the experimental demonstration of a reference-free Distributed Anti-Stokes Raman Thermometry (DART) scheme for real-time power line monitoring in overhead power transmission (OPGW/OPC) cables. Our work is based on the loop configuration in which only the anti-Stokes intensity is captured and processed to determine the temperature, thereby providing a self-calibrated solution that is tailor-made for a rugged field measurement. Temperature experienced by the optical fiber embedded in the power cable is estimated through a simple heat transfer model and is experimentally validated using a homebuilt DART system with a root mean square (RMS) temperature error of 0.33 °C.

A High Accuracy Preserving Parallel Algorithm for Compact Schemes for DNS

Abstract: A new accuracy-preserving parallel algorithm employing compact schemes is presented for direct numerical simulation of the Navier-Stokes equations. Here the connotation of accuracy preservation is having the same level of accuracy obtained by the proposed parallel compact scheme, as the sequential code with the same compact scheme. Additional loss of accuracy in parallel compact schemes arises due to necessary boundary closures at sub-domain boundaries. An attempt to circumvent this has been done in the past by the use of Schwarz domain decomposition and compact filters in “A new compact scheme for parallel computing using domain decomposition,” J. Comput. Phys. 220, 2 (2007), 654--677, where a large number of overlap points was necessary to reduce error. A parallel compact scheme with staggered grids has been used to report direct numerical simulation of transition and turbulence by the Schwarz domain decomposition method. In the present research, we propose a new parallel algorithm with two benefits. First, the number of overlap points is reduced to a single common boundary point between any two neighboring sub-domains, thereby saving the number of points used, with resultant speed-up. Second, with a proper design, errors arising due to sub-domain boundary closure schemes are reduced to a user designed error tolerance, bringing the new parallel scheme on par with sequential computing. Error reduction is achieved by using global spectral analysis, introduced in “Analysis of central and upwind compact schemes,” J. Comput. Phys. 192, 2, (2003) 677--694, which analyzes any discrete computing method in the full domain integrally. The design of the parallel compact scheme is explained, followed by a demonstration of the accuracy of the method by solving benchmark flows: (1) periodic two-dimensional Taylor-Green vortex problem; (2) flow inside two-dimensional square lid-driven cavity (LDC) at high Reynolds number; and (3) flow inside a non-periodic three-dimensional cubic LDC with the staggered grid arrangement.

Low-Temperature Propylene Epoxidation Activity of CuO-CeO2 Catalyst with CO + O2: Role of Metal-Support Interaction on the Reducibility and Catalytic Property of CuOx Species

Abstract: Epoxidation of propylene into propylene oxide (PO) in the gas phase is a highly challenging reaction. Cu-based catalysts have been active for this reaction, but the state of Cu as an active species...

Processing of Cf/SiC composites by hot pressing using polymer binders followed by polymer impregnation and pyrolysis

Abstract: Continuous carbon fiber (Cf) reinforced silicon carbide (SiC) matrix composite (Cf/SiC) was processed through hot pressing (HP) using polycarbosilane (PCS) in matrix and polysilazane in interphase regions as polymer binders. HP experiments were conducted at 4 MPa, 1200 °C and 1 h; followed by PCS polymer impregnation and pyrolysis (PIP) at 1200 °C under vacuum. The BN/SiC-Si3N4 interphase formed on the Cf cloth during BN dispersed polysilazane polymer coating and pyrolysis. The influence of PCS quantity during HP experiments on Cf/SiC composites was studied. Results suggest that sintering of SiC matrix in Cf/SiC composite improves by increasing PCS content during HP; however, high PCS content increases the liquidity of SiC-PCS mixture to flow out of the composite structure. The Cf/SiC composites with relative density ranging from 79 to 83% and flexural strength from 67 to 138 MPa was achieved.

Microstructural evolution in Al–Mg–Sc alloy (AA5024): Effect of thermal treatment, compression deformation and friction stir welding

Abstract: Effect of thermal annealing and deformation in both compression and friction stir welding conditions on microstructural evolution in the cold rolled Al-4.36Mg-0.26Sc-0.09Zr (wt.%) alloy was investigated. To evaluate the thermal stability of the alloy, differential scanning calorimetry and static annealing experiments were carried out as a function of temperature. Microhardness measurements and quasi-static compression testing were performed on the as-received and annealed alloy samples. Friction stir welding was carried out on the as-received alloy sheet in butt configuration at two different tool traverse speeds of 250 and 500 mm/min. Upon annealing, the alloy showed continuous recrystallization with transformation of the elongated grain structure possessing strong rolling texture to coarse equiaxed microstructure with random orientation. The annealed alloy exhibited reduced hardness and compressive strength at room temperature. Detailed microstructural investigation of hot compression deformed and friction stir welded samples revealed formation of subgrain structure and followed by fine recrystallized grains with nearly random orientation. The analysis suggests that continuous dynamic recrystallization involving progressive subgrain rotation is the possible mechanism for microstructural changes occurring during hot deformation of Al–Mg-Sc alloy.

Hydrothermal synthesis of ZnO nanotubes for CO gas sensing

Abstract: Carbon monoxide (CO) gas sensing response of hydrothermally synthesized hexagonal ZnO nanostructures was examined with respect to its morphologies. Synthesized ZnO nanostructures were characterized by X-Ray diffraction (XRD), Field Emission Scanning Electron Microscope (FE-SEM), Energy Dispersive X- Ray Analysis (EDAX) and UV Visible spectroscopic techniques. The CO gas sensing response of ZnO nanostructures were investigated as change in resistance at different gas concentrations of 2, 4, and 6 ppm at room temperature (25 oC). ZnO nanostructures have shown high response to CO concentrations as low as 6 ppm. Response 1.7 s, 2 s and 3 s and recovery time was 2 s, 3 s, 4 s, respectively, for 2, 4 and 6 ppm. Response of the CO gas for ZnO nanostructures at room temperature (25 oC) was 75 %.

Effect of the addition of diurethane dimethacrylate on the chemical and mechanical properties of tBA-PEGDMA acrylate based shape memory polymer network.

Abstract: There is a great demand for the synthesis of acrylate based thermoset shape memory polymer (SMP) associated with one monomer and one crosslinker such as tert-butyl acrylate (t-BA) with poly (ethylene glycol) dimethacrylate (PEGDMA). The present work describes the synthesis of a new thermoset SMP wherein a second monomer such as diurethane dimethacrylate (DUDMA) has been added to the existing tBA + PEGDMA SMP matrix. The synthesized thermoset shape memory polymer exhibited a glass transition temperature (Tg) of 55 °C, higher Young's Modulus of 3.23 GPa, transmittance of 95% and 100% shape recovery. The SMP exhibited response to both thermal and chemical stimuli. The shape recovery rate of the SMP network is 20 s compared to 24 s observed for SMP based on tBA + PEGDMA. The obtained SMP is very transparent and possesses higher stiffness (8 MPa) and hence may be suitable for biomedical shape memory lens and orthopedic application.

Rheological properties of concentrated polyacrylonitrile co-polymer and lignin blend solution

Abstract: Polyacrylonitrile copolymers with different molecular weights (Mws) are synthesised by aqueous free-radical redox polymerisation technique. Polyacrylonitrile (PAN) and lignin-blended solutions are prepared in dimethyl sulphoxide solvent by varying the polyacrylonitrile/lignin content. The effect of lignin addition to PAN copolymer having different weight-average Mws on the rheological properties is explored. Rheological measurements indicate that the solution viscosity reduces with the increase in the lignin content. The Cole–Cole plot or Han plot and Casson plot are used to characterise the solution homogeneity. The slope value of the plot suggests that the molecular-level homogeneity of the solution is not affected much by the addition of lignin. Thermal-induced gelation of concentrated solution has been rheologically investigated to avoid overheating of solution during the dissolution, storage and transportation for further wet spinning process.

Citrate combustion synthesized Al-doped CaCu3Ti4O12 quadruple perovskite: synthesis, characterization and multifunctional properties

Abstract: Correction for 'Citrate combustion synthesized Al-doped CaCu3Ti4O12 quadruple perovskite: synthesis, characterization and multifunctional properties' by Kamalesh Pal et al., Phys. Chem. Chem. Phys., 2020, 22, 3499-3511, DOI: 10.1039/C9CP05005A.

Effect of hygrothermal aging on the mechanical properties of IMA/M21E aircraft-grade CFRP composite:

Abstract: Unidirectional carbon fiber-reinforced plastic (CFRP) IMA/M21E polymer composite was manufactured by standard autoclave curing method. This is a new aircraft-grade CFRP composite presently used in ...

Radar Absorbing Structures Using Frequency Selective Surfaces: Trends and Perspectives

Abstract: Microwave radar absorbers are widely used in the strategic sector and wireless communication systems to reduce the radar cross-section of a target and electromagnetic interferences, respectively. For airborne stealth platforms, it is desired to have wide bandwidth RAS with minimum thickness and adequate structural rigidity. However, the classical RAS structures are thicker with a narrowband of absorption. So the demand of thin and broadband absorber for a modern stealth platform can be accomplished by designing metallic or resistive frequency selective surfaces (FSSs) based radar absorbing structures (RAS). In view of this, a technological assessment on frequency selective surface (FSS)-based radar absorbing structure are presented in this paper, which includes historical review on radar absorber development, design techniques, physical models, and optimization techniques. Ultra-wideband absorbers with essentially thin structures can be realized by optimizing FSS and dielectric parameters. The genetic algorithm (GA) is identified as one of the effective searching algorithms among several numerical algorithms, which are discussed in detail for single and multi-layered FSS–RAS. The fabrication techniques of resistive FSS by printing the periodic pattern using resistivity-controlled ink is also addressed. For proof-of-the concept, a prototype of cross-dipole FSS based RAS is fabricated and measured.

Self-healing microcapsules encapsulated with carbon nanotubes for improved thermal and electrical properties

Abstract: Microcapsules are widely used by researchers in self-healing composites. In this study, multi-walled carbon nanotubes (CNT) were incorporated into the core of the microcapsules, along with the self-healing agent. Dicyclopentadiene (DCPD) and urea-formaldehyde (UF) were chosen as the core and shell materials respectively, and DCPD–CNT–UF based dual core microcapsules were synthesized. Two types of microcapsules, namely, DCPD–UF and DCPD–CNT–UF were successfully synthesized by the in situ polymerization technique. The novelty of this work is the development of dual core microcapsules with DCPD–CNT–UF combination. Surface morphology characterization and elemental analysis of the microcapsules were carried out using a scanning electron microscope (SEM-EDX). TGA and DSC analysis show that DCPD–CNT–UF microcapsules have better thermal stability than DCPD–UF microcapsules. These novel DCPD–CNT–UF microcapsules were found to be compatible with epoxy base resin for making resin castings. The presence of CNT is found to improve the mechanical, thermal and electrical properties of the resin cast specimens without compromising on self-healing efficiency.

Resistive FSS based Radar Absorbing Structure for Broadband Applications

Abstract: With rapid advancements in the field of target detection technologies, there is increased demand for radar absorbing materials with superior power absorption characteristics. However, the development of broadband, structurally stable and lightweight absorber which would function in the entire range of 2 GHz-18 GHz is still a herculean task. Resistive frequency selective surface (FSS) based absorbers present an efficient class of radar absorbing structures (RAS) where both ohmic losses as well as dielectric losses contribute towards achieving broadband absorption performance at reduced thickness. In this regard, the present paper proposes multi-layered RAS based on resistive FSS for broadband applications. Full wave simulation results clearly indicate that the percentage of power absorbed is greater than 90% over a broadband frequency range (2GHz to 22 GHz).