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Dey A.,Thermal Systems Group | Mukhopadhyay A.K.,Indian Central Glass and Ceramic Research Institute
Ceramics International | Year: 2014

The evaluation of residual stress in bioactive hydroxyapatite (HAP) ceramic coating by nanoindentation technique has been attempted successfully for the very first time ever in the present work. The HAP coatings were deposited on surgical grade 316 L austenitic stainless steel and Ti-6Al-4V substrates by microplasma spraying (MIPS) process. The coatings had Ca/P ratio of 1.67 and were ∼80-90% crystalline. The results showed a residual compressive stress of ∼22 MPa for the MIPS-HAP coatings on the SS316L substrates. For the coatings deposited on the Ti-6Al-4V substrates, however, a residual tensile stress of ∼11 MPa was estimated. These data matched well with those obtained by XRD based technique. Thus, favorable data comparison provides further support to the efficacy of the nanoindentation based technique utilized in the present work for residual stress estimations. © 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Source

Bandyopadhyay P.,Indian Central Glass and Ceramic Research Institute | Dey A.,Indian Central Glass and Ceramic Research Institute | Dey A.,Thermal Systems Group | Roy S.,Indian Central Glass and Ceramic Research Institute | Mukhopadhyay A.K.,Indian Central Glass and Ceramic Research Institute
Journal of Non-Crystalline Solids | Year: 2012

Today the technological applications of glass span from everyday life to many advanced areas. These advanced applications require very accurate grinding and polishing that involve controlled removal of glass to achieve micron or even sub-micron surface finish. The major bottleneck in this connection is that the material removal mechanisms during such processes are yet to be fully understood. Since grinding involves many single pass scratch processes happening simultaneously, to develop better understanding about the effect of the normal load in affecting the material removal mechanisms; a number of single pass scratch experiments were conducted on a commercially available soda lime silica glass as a function of various normal loads (2-15 N) at a constant scratch speed of 100 μm.s - 1. The results showed that the tribological properties, the severity and the spatial density of damage evolution were sensitive to the applied normal loads and the resultant tensile as well as shear stresses. Extensive optical and scanning electron photomicrography of the surface and sub-surface deformation zones proved the existence of three distinct deformation zones in the immediate vicinity of the scratch grooves and led to the development of a qualitative model of the material removal mechanisms. © 2012 Elsevier B.V. Source

Karthikeyan B.,Annamalai University | Ramanathan S.,Annamalai University | Ramakrishnan V.,Thermal Systems Group
Materials and Design | Year: 2010

The need for lightweight, dimensionally stable materials for critical aerospace applications opened new frontiers of advanced materials. Metal-matrix composites can withstand the extreme conditions often encountered in space environment. The metal-matrix composites have been developed indigenously and tested in Thermo Mechanical Analyser (TMA). The measurement and characterization of thermo physical properties of MMC such as density, coefficient of thermal expansion (CTE), specific heat (Cp) and thermal conductivity plays a important role. It is essential to evaluate the new material for thermal stability and to evaluate CTE before actual use. Experimentally the CTE can be measured by TMA under the absolute methods. The experiments have been carried out in the temperature range -125°C to 550°C. The measurements of the thermal properties of materials help better understanding of the thermal design. Stir casting technique was used to fabricate the 7075 Aluminium Alloy and 7075 Al with different volume fractions of SiCp composites. The composites exhibited lower coefficient of expansion values than the alloy. © 2009 Elsevier Ltd. Source

Banker N.D.,Indian Institute of Science | Prasad M.,Thermal Systems Group | Dutta P.,Indian Institute of Science | Srinivasan K.,Indian Institute of Science
Applied Thermal Engineering | Year: 2010

A laboratory model of a thermally driven adsorption refrigeration system with activated carbon as the adsorbent and 1,1,1,2-tetrafluoroethane (HFC 134a) as the refrigerant was developed. The single stage compression system has an ensemble of four adsorbers packed with Maxsorb II specimen of activated carbon that provide a near continuous flow which caters to a cooling load of up to 5 W in the 5-18 °C region. The objective was to utilise the low grade thermal energy to drive a refrigeration system that can be used to cool some critical electronic components. The laboratory model was tested for its performance at various cooling loads with the heat source temperature from 73 to 93 °C. The pressure transients during heating and cooling phases were traced. The cyclic steady state and transient performance data are presented. © 2010 Elsevier Ltd. All rights reserved. Source

Sharma A.K.,Thermal Systems Group | Sridhara N.,Thermal Systems Group
Advances in Space Research | Year: 2012

A spacecraft with a passive thermal control system utilizes various thermal control materials to maintain temperatures within safe operating limits Materials used for spacecraft applications are exposed to harsh space environments such as ultraviolet (UV) and particle (electron, proton) irradiation and atomic oxygen (AO), undergo physical damage and thermal degradation, which must be considered for spacecraft thermal design optimization and cost effectiveness This paper describes the effect of synergistic radiation on some of the important thermal control materials to verify the assumptions of beginning-of-life (BOL) and end-of-life (EOL) properties Studies on the degradation in the optical properties (solar absorptance and infrared emittance) of some important thermal control materials exposed to simulated radiative geostationary space environment are discussed The current studies are purely related to the influence of radiation on the degradation of the materials; other environmental aspects (e.g.; thermal cycling) are not discussed The thermal control materials investigated herein include different kind of second-surface mirrors, white anodizing, white paints, black paints, multilayer insulation materials, varnish coated aluminized polyimide, germanium coated polyimide, polyether ether ketone (PEEK) and poly tetra fluoro ethylene (PTFE) For this purpose, a test in the constant vacuum was performed reproducing a three year radiative space environment exposure, including ultraviolet and charged particle effects on North/South panels of a geostationary three-axis stabilized spacecraft Reflectance spectra were measured in situ in the solar range (250-2500 nm) and the corresponding solar absorptance values were calculated The test methodology and the degradations of the materials are discussed The most important degradations among the low solar absorptance materials were found in the white paints whereas the rigid optical solar reflectors remained quite stable Among the high solar absorptance elements, as such the change in the solar absorptance was very low, in particular the germanium coated polyimide was found highly stable © 2012 COSPAR Published by Elsevier Ltd All rights reserved. Source

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