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Khatavkar N.,Indian Institute of Technology BHU Varanasi | Balasubramanian K.,DIAT DU
RSC Advances | Year: 2016

Encompassment of radar communication in modern avionics provides the backbone for safe flight and tactical warfare. In the past few decades radar technology has achieved commendable precision and sophistication, but efficient communication relies upon effective transmission of electromagnetic waves through materials shielding the antenna and exhibiting high transparency for radio/microwaves. Since the structure of radomes in supersonic aircraft is dominated by aerodynamic standards, numerous challenges are encountered while selecting the materials apposite for construction having superior mechanical strength and resilience while displaying the minimum influence on the transmission profile of radio waves. The radome structure of aircrafts is subjected to sudden acceleration, drag forces and erosion due to rain and dust, which change the transmission characteristics due to change in shape/thickness of the structure. The problems are further complicated by the advent of supersonic/hypersonic aircrafts and missiles where high strength preservation and structural integrity is necessary at temperatures in excess of 350 °C. This review systematically throws light on the composite materials and existing technologies employed for the fabrication of high strength, low dielectric loss sandwich radomes for supersonic aircrafts. © The Royal Society of Chemistry 2016.

Badhe Y.,DIAT DU | Balasubramanian K.,DIAT DU
RSC Advances | Year: 2014

Numerous disasters of re-entry vehicles because of high kinetic and frictional forces have paved the way for the enhancement of thermal protection systems (TPS). These TPS protect the structures and payloads of re-entry probes during hypersonic flight from space to a planetary atmosphere, and insulate the surface by sacrificial pyrolysis and concomitant formation of tough refractory char over the surface of the insulator. The present perspective demonstrates the development of a novel hybrid composite of resorcinol formaldehyde with an ultra high temperature ceramic (UHTC), silicon carbide, aiming at fulfilling the thermal requirements of ablation resistant composite coatings with improved tenacity and adhesion to the substrate. These composites were synthesized via an in situ polymerization, which ensures molecular level dispersion. The ablation resistance with respect to mass loss was quantified by testing under an oxyacetylene flame up to 2300 °C for 60 s, which imitates the conditions of re-entry systems, notably reducing the mass ablation rate and linear ablation rates by 44 and 76%, respectively. The improved ablation resistance of SiC-RF can be attributed to the formation of glassy, fused nano silica upon its thermal oxidation, and effectively blocks oxygen from attacking the matrix. X-ray diffraction studies reveal and confirm the formation of SiO2, which protectively cover the surface and peaks at 24° and 44° attributing to (002) and (100), respectively, for turbostratic carbon formed during pyrolysis. FESEM imaging was employed to study surface topography, which confirms the same and reveals fused structures on carbonized surfaces and EDAX, quantitatively substantiating the presence of silica. TGA measurements, consummated up to 800 °C, show that the incorporation of well-dispersed SiC results in an increase in char residues up to 23% with respect to pristine RF, and a consistent improvement in thermal stability with an increase in concentration is evident. The results prove that the incorporation of silicon carbide exhibits positive effects on improving the ablation resistance and thermal properties of the RF resin by promoting the formation of fused nano silica structures on the surface. © 2014 The Royal Society of Chemistry.

Kushwaha N.,DIAT DU | Kumar R.,ARDE
IET Microwaves, Antennas and Propagation | Year: 2015

In this study, a new compact coplanar waveguide-fed wideband circularly polarised slot antenna is designed and fabricated. To achieve circular polarisation, the slot in the ground plane is truncated at one corner and excited by a modified L-shaped radiating element. To achieve wide axial ratio bandwidth (ARBW), one end of the L-shaped patch is connected with the ground via a slit. The ARBW is further improved by properly placing two additional narrow slots in the ground plane. The measured impedance bandwidth and ARBW at boresight are achieved 87.2% (from 2.2 to 5.6 GHz) and 81.05% (from 2.2 to 5.2 GHz), respectively. For the better understanding, the surface current distribution and parametric studies are presented. To characterise the antenna in the time domain, group delay and system fidelity factor (SFF) are measured. The measured group delay has less variation (of 0.5 ns) in the operating band and the measured SFF is found to be 0.89. The measured and simulated results are in good agreement. © 2015. The Institution of Engineering and Technology.

Krishna R.V.S.R.,DIAT DU | Kumar R.,ARDE
Journal of Electromagnetic Waves and Applications | Year: 2016

A V-shape slot antenna for dual slant polarization is proposed. The slot is the union of two stepped rectangular slots tilted at ±45° with the vertical. Each section of the slot is excited using a microstrip feed line printed on the other side of the substrate. The feed is also stepped and bent so as to cross the slot at right angles. The decoupling between the ports is provided by means of narrow rectangular stubs placed at the intersection of the slot arms. Measurements taken on the fabricated prototype indicate an impedance bandwidth from 3.3 to 12 GHz with isolation better than 15 dB across the band. The aperture electric field distributions as well as far field radiation patterns are used to verify the dual slant polarization achieved with the antenna. The time domain characterization of the antenna is done by calculating the fidelity factor which is found to be >0.75 indicating suitability of the antenna for pulse transmission. For determining the diversity behavior, the envelope correlation coefficient is calculated and found to be below 0.004. The antenna has a peak gain from 4 to 6 dBi. A modified design of the antenna is also presented with impedance bandwidth from 3 to 12 GHz and isolation better than 20 dB from 3.7 GHz onwards. With compact features and wideband return loss and isolation, the antennas are expected to be useful for diversity applications in ultra wideband communication devices such as MIMO wifi, imaging radars, and polarimetric sensing devices. © 2016 Informa UK Limited, trading as Taylor & Francis Group

Kumar R.,ARDE | Naidu P.V.,Symbiosis International University | Kamble V.,DIAT DU
Progress In Electromagnetics Research B | Year: 2014

A compact, coplanar waveguide (CPW) fed asymmetric slot antenna with dual operating bands is proposed. The slot is modi-ed rectangular in shape and asymmetrically cut in the ground plane. A hexagonal patch fed by a two-step CPW is used to excite the slot. The feed itself is slightly asymmetric (shifted, with unequal ground planes). The asymmetric cuts on the slot together with the feed line asymmetry have helped in obtaining ultra wideband impedance matching. An extra resonance at 2.4 GHz for Bluetooth applications is obtained by cutting an additional meandered narrow rectangular shape slit in the ground plane. The prototype of the proposed antenna has been fabricated and tested. The measured 10 dB return loss bandwidth of the proposed antenna is 200MHz (2.3-2.5 GHz) for the -rst band and 12.1 GHz (2.9-15.0 GHz) for the second band. The radiation patterns of the proposed antenna are obtained and found to be Omni-directional in H-plane and bi-directional in E-plane. The measured and simulated results are in good agreement.

Badhe Y.,DIAT DU | Balasubramanian K.,DIAT DU
RSC Advances | Year: 2014

Successful utilization of thermosetting resins as ablative materials for heat shields in thermal protection systems (TPS) has newer contemporary materials, surpassing the conventional resins in terms of thermal and physical properties. The present study demonstrates similar progress in ablative heat shielding materials, putting forward capable replacements for existing phenolic system. A novel three-dimensional network composed of a dihydric resorcinol formaldehyde (RF) has been synthesized successfully by modification with boric acid via an effortless and facile polymerization technique. The ablation and thermal properties were investigated with primary and cheap, yet effective test methods like the oxy-acetylene flame test, which explored the ablation rate in terms of mass loss and dimensional change, showing 40% and 70% curtailment respectively. X-Ray diffraction studies confirm the formation of insulative, turbostratic, carbonaceous char formed upon resin pyrolysis with peaks at 24°and 44°attributing to (002) and (100) for turbostratic carbon formed during pyrolysis. FTIR studies reveal change in the intensity and shifts in the peaks for pristine RF for the boric acid modified RF including stretch vibrations at 1429 and 1380 cm-1 corroborating modification of the ring. Atomic Force Microscopy showed the surface roughness which up surged with an increase in the concentration of boric acid in the system, making the composite sensitive to mechanical depletion due to increase reactivity. Interesting morphologies of the sample after ablation were observed with FESEM exposing glassy nanospheres of borate in the periphery and porous char of the depleted zone. Pristine RF has a char yield of 42%, which increased to 68% for 50 wt% of boric acid in RF at 800 °C, quantified by the TGA studies. Mathematical models and energy balance equations were idealized for the exchange in energies at the surface of the ablator. The results determined that the modification of the 3D network of the resin justifies its competency to replace conventional materials demonstrating augmented ablation resistance with faster reaction mechanisms. This journal is © the Partner Organisations 2014.

Banerjee B.S.,DIAT DU | Khaira S.S.,Sri Guru Granth Sahib World University | Balasubramanian K.,DIAT DU
RSC Advances | Year: 2014

The configuration of thin film polycarbonate (PC) is formulated, aiming for a financially efficient approach of the solvent casting method by grafting waste fly ash cenosphere (FAC) encapsulated with tetraethoxysilane (TEOS) as a grafting agent. The research study emphasized on the routine practice of controlled thermal dissipative electronic widgets by a systematic characterization analysis. FTIR exemplifies the surface adherence characteristics of the GFAC (Grafted Fly Ash Cenosphere) over PC, by confirming the efficient grafting between silane and FAC at 2950 cm-1 due to the flexible vibrations by the -OH group. The PC-FAC composite showed the characteristic triplet signature peaks of PC at 1152, 1188 and 1227 cm-1. Following the hierarchy, the morphological study analyzes the surface molecular interaction between the PC/GFAC and their electronic properties by FESEM. AFM confers the topographical study of pristine PC, which measures the surface roughness of pristine PC as 4.5 nm which mitigates to 0.7 nm for the PC/GFAC and justifies the homogenous dispersion of GFAC in PC, thus directing the consequential study of TGA. It examines controlled surface thermal conduction and authenticates the noble thermal stability of the PC/GFAC with a char yield of 36% (approximately more than twice that of pristine PC) at 800°C by TGA. The PC/GFAC affirms a 70°C lag in the onset of thermal degradation, at 430°C, as compared with pristine PC, which starts to decompose at 360°C. Thus, the silane grafted nano composites of PC expands the operable temperature range for the electronic elemental properties usage. The present investigation procures attention on the thermal characteristics of the PC/GFAC, illustrated by the conduction modeling parameter across the spherical wall of the cenosphere and the interfacial heat transfer for the PC/GFAC composite, pertaining to a worthwhile and serviceable thermal management praxis. © 2014 The Royal Society of Chemistry.

Katiyar N.,DIAT DU | Balasubramanian K.,DIAT DU
RSC Advances | Year: 2014

The disposal of Fly ash cenosphere is a heavy challenge for various coal and thermal power plants. In this perspective, the present research work aims at using the waste product of the thermal power plants as filler in engineering plastic as an alternative to thermosets as matrices for high performance composites. The Fly ash cenosphere (FAC) fillers reinforced polycarbonate (PC) composites were fabricated using an economically and environmentally viable method of melt extrusion with varying concentration of filler as 5, 10, 20, 30, 40 and 50 wt%. FESEM were carried out to examine the morphology of the composite, which reflects a good dispersion and strong interfacial interaction between PC and modified FAC than the unmodified counterpart. The characteristic peaks at 2363 and 2930 cm-1 in the FTIR corroborate the interaction between cenosphere particles and the silane coupling agent. Thermogravimetric analysis (TGA) substantiate that PC-FAC had good thermal stability with a high char yield of 70% (which is almost thrice than that for unfilled PC) at 700 °C in a nitrogen atmosphere. The XRD pattern displays the characteristic peaks at (002) (100) and (110) which affirms the presence of turbostratic carbon with a crumbled hexagonal structure. Effective thermal conductivity of the composite was mathematically expressed by the Maxwell model of thermal conductivity and the computed value was 0.13 W m-1 °C, with a 29% decrement compared to pristine PC. This journal is © the Partner Organisations 2014.

Banerjee B.S.,DIAT DU | Balasubramanian K.,DIAT DU
RSC Advances | Year: 2015

Nanoscale texturing of a nano-hydroxyapatite (n-HA) filler on a polycarbonate (PC) matrix is ameliorated by advanced engineered spray techniques viz. spray gun and centrifuged spray drying, concerned with modifying topographical properties for biomedical grade screw/plate coating application. Mathematical evaluation of the factors affecting the texture of the thin film PC/n-HA nanocomposite has been modelled for the centrifuged spray dryer concerning homogeneity and symmetric dispersion of n-HA pitching on the PC medium. FTIR illustrates the functional group vibration peaks of 1093 cm-1 and 603 cm-1 of PC/n-HA nanocomposites due to the presence of PO4 3-. XRD infers the average crystal size of n-HA ≤20 nm in the PC/n-HA nanocomposite, which possesses consistency in the FESEM micrograph, confirming the various dispersion comparisons between spray gun film and centrifuged spray dried film. Topographical analysis of PC/n-HA film acquired by the two modes of spraying exemplifies surface roughness of 81.4 nm by the spray gun and 132 nm by the centrifuged spray dryer technique, with increasing spikes affirming the uniform scaffold structure of the n-HA embedment over the PC medium, thus, providing the hydrophobic trait needed for corrosion resistant application. Contact angle analysis shows the wettability and adhesive property of the PC/n-HA nanocomposite and delivers a 131.7° contact angle for innovative centrifuged spray dryer technique. Hence, the modelled parameters emphasize the applicability of the innovative designed centrifuged spray dryer technique for biomedical coating applications. This journal is © The Royal Society of Chemistry 2015.

Thakur D.G.,DIAT DU | Ramamoorthy B.,Indian Institute of Technology Madras | Vijayaraghavan L.,Indian Institute of Technology Madras
International Journal of Advanced Manufacturing Technology | Year: 2012

The use of superalloy Inconel 718 is increasing in most of the sophisticated applications like aircraft engines, industrial gas turbines, rocket engines, space vehicles, submarines, etc. Hence, in-depth understanding of this material helps to determine the ability of this material to withstand severe conditions of stress, temperature, corrosion, and controls its longevity and reliability. In the present work, an attempt has been made to study the relationship of degree of work hardening and tool life as a function of cutting parameters like cutting speed, feed, depth of cut, untreated tungsten carbide and postcryogenic-treated tool. Work hardening and tool life are the major factors which need to be controlled/improved to enhance the machinability characteristics of superalloy Inconel 718. A significant performance in tool life was observed due to cryogenic treatment given to tungsten carbide tool. Moreover, it was observed that optimized cutting parameters not only minimized/controlled work hardening characteristics but also improved tool life while high-speed machining of Inconel 718. © Springer-Verlag London Limited 2011.

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