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Prabhu T.R.,Center for Military Airworthiness and Certification
Bulletin of Materials Science | Year: 2015

Discrete functionally graded composites are the novel composites which have high potential in the brake friction material applications. In this paper, we have prepared discrete functional graded Cu/10%SiC/ 20%graphite(Gr)/10%boron nitride (h-BN) hybrid composites by the layer stacking compaction and pressure sintering techniques. We have considered two types of composites based on h-BN particle sizes. The size ranges of h-BN used were 140-180 and 3-25 μm. The friction and wear properties of the composites were evaluated in a laboratory scale brake inertial dynamometer at low (5, 10 m s-1) and high sliding speeds (30, 35 m s-1) and, high braking load (2000 N) conditions. In addition, we have performed microstructure characterization, density, hardness and flexural strength measurements. Wear surface morphology studies were also carried out using stereoscope and scanning electron microscope. Our experiments lead to the following important results: (1) the large size h-BN particle improves the densification of the hybridized composite layer and provides higher wear resistance and better braking performance at all sliding speeds, (2) the wear loss (by mass) and the stopping distance/time increase with sliding speeds due to the increase in the braking energy, (3) at low sliding speeds (5, 10 m s-1), abrasive wear is the main wear mechanism, whereas many different wear mechanisms (delamination, oxidation, abrasive) are cooccuring at higher sliding speeds (30, 35 m s-1), (4) the mechanical properties (flexural strength and surface hardness) of composites are not affected by the h-BN particle size, (5) the incorporation of copper layer in the discrete layer structure deflects and arrests the crack at the copper/composite layer interface, thus improving the fracture resistance in addition to improving the bulk thermal conductivity. © Indian Academy of Sciences. Source


Mishra R.K.,Center for Military Airworthiness and Certification
Proceedings of the ASME Turbo Expo | Year: 2010

Qualification of afterburner thrust augmentation system in stand-alone mode prior to its flight trials plays a vital role in aero engine application. A full-scale afterburner system was studied to demonstrate its performance parameters such as pressure loss, combustion efficiency, liner temperature at full and part load conditions. Light-off characteristics at different altitude-flight Mach combination were also established. The afterburner system also was activated for considerable time to validate its integrity and performance. The paper presents the various tests carried out on the afterburner and their results. The paper also highlights the jet nozzle matching at various throttle position and studies on combustion instability from qualification point of view. Satisfactory demonstration of performance of the afterburner without encountering screech or buzz over the operating range qualifies the system for its application in the aero engine for limited operation. Copyright © 2010 by ASME. Source


Samuel M.P.,Center for Military Airworthiness and Certification | Srivastava S.,Gas Turbine Research Establishment
International Journal of Performability Engineering | Year: 2013

In this paper a few issues of handling maintenance inventory with heterogeneous part characteristics have been discussed. A typical aeroengine having several years of operational history has been utilized to highlight the differential inventory management approach based on the relative significance of the parts. The replacement rate of the operationally significant components has been evaluated using the maintenance data and it serves as a direct input for assessing the dynamic demand for spare parts. In the overall view, this paper documents the process of identifying the operationally significant high value components, assessing their spares requirement under realistic operational/maintenance conditions and managing the maintenance inventory in a simple manner. © RAMS Consultants. Source


Samuel M.P.,Center for Military Airworthiness and Certification
Defence Science Journal | Year: 2014

The helicopters used for marine operations encounter harsh environment laden with salt mist, sand and dust which could accelerate the deterioration of components. Assessment of the effect of operational environment on component degradation of such helicopter engines is crucial in scheduling their maintenance and ensuring flight safety. The objective of this study is to understand and assess the differential degradation pattern of aeroengines operated in marine environment in comparison to their counterparts operated in non-marine environment. In this study, a sample of 257 ex-service aeroengines of same type and make, operated in marine and non-marine environment were randomly selected and their degradation pattern observed. After obtaining the data on component degradation, further statistical analysis was carried out and the statistical significance of the observations were computed. Out of the ten major components considered in this study, five of them were found to have statistically significant differential degradation due to operation in marine environment. For the remaining components adequate evidence was not available to substantiate differential degradation due to operation in marine environment. These findings serve as valuable input for maintenance inventory planning as well as component improvement programme. © 2014, DESIDOC. Source


Zafir Alam M.D.,Defence Metallurgical Research Laboratory | Hazari N.,Defence Metallurgical Research Laboratory | Varma V.K.,Center for Military Airworthiness and Certification | Das D.K.,Defence Metallurgical Research Laboratory
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011

The tensile behavior of a directionally solidified (DS) Ni-base superalloy, namely, CM-247LC, was evaluated in the presence of a Pt-aluminide bond coat. The effect of the thermal cycling exposure of the coated alloy at 1373 K (1100 °C) on its tensile properties was examined. The tensile properties were evaluated at a temperature of 1143 K (870 °C). The presence of the bond coating caused an approximately 8 pct drop in the strength of the alloy in the as-coated condition. However, the coating did not appreciably affect the tensile ductility of the substrate alloy. The bond coat prevented oxidation-related surface damage to the superalloy during thermal cycling exposure in air at 1373 K (1100 °C). Such cyclic oxidation exposure (up to 750 hours) did not cause any further reduction in yield strength (YS) of the coated alloy. There was a marginal decrease in the ultimate tensile strength (UTS) with increased exposure duration. Because of the oxidation protection provided by the bond coat, the drastic loss in ductility of the alloy, which would have happened in the absence of the coating, was prevented. © 2011 The Minerals, Metals & Materials Society and ASM International. Source

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