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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.

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.

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.

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.

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.

Ram Prabhu T.,Center for Military Airworthiness and Certification | Varma V.K.,Center for Military Airworthiness and Certification | Vedantam S.,Indian Institute of Technology Madras
Wear | Year: 2014

In this paper we studied the tribological behavior of iron matrix composites at high sliding speeds (25-35. m/s) typical of aircraft braking conditions. We developed two types of Fe matrix composites with different elastic modulus reinforcements: silica (71. GPa) and mullite (143. GPa) particulates using powder metallurgy. Two different size ranges: large (150 - 250 μm) and small sizes (1 - 10 μm) and a range of volume fractions of the particulates were also considered. The dry sliding wear and braking performance of the composites were investigated using a sub-scale disc braking dynamometer. The wear tests of the composites show that large size and high volume fraction of reinforcement particles provides better wear resistance and braking performance at high sliding speed conditions (25. m/s-35. m/s) for both Fe/silica composites and Fe/mullite composites. Significantly, Fe/mullite composites at lower volume fractions showed greater wear resistance than the Fe/silica composites due to the higher elastic modulus of the mullite particles. A wear track examination of composites showed that different wear mechanisms were operative at the different speeds. Our results indicate that composites with a high volume fraction of large sized reinforcement particles of high elastic modulus are to be preferred for braking performance and low wear loss at high sliding speed applications. © 2013 Elsevier B.V.

Ram Prabhu T.,Center for Military Airworthiness and Certification | Varma V.K.,Center for Military Airworthiness and Certification | Vedantam S.,Indian Institute of Technology Madras
Wear | Year: 2014

In this work we investigated the friction and wear properties of Fe/SiC/graphite hybrid composites using a sub-scale dynamometer disk brake testing system. Two particle size ranges (1-30μm and 150-180μm) and three particle volume fractions (10%, 15% and 20%) of SiC were considered. The sliding speed conditions considered in this study (25-35 m/s) were comparable to that experienced by brake materials in high speed braking applications in aircrafts, race car and high speed trains. We examined the effect of coating the SiC particles with BaSO4 to improve interfacial properties and prevent potential undesirable interfacial reactions. The wear loss was found to decrease with increasing volume fraction of SiC for all particulate sizes. At low sliding speeds the composites with large particle sizes and high volume fractions were found to be more effective in controlling wear. On the other hand, at higher sliding speeds the high volume fraction composites were found to be more effective in controlling wear for all particle sizes. This is attributed to a transition in the wear mechanism at higher sliding speeds. © 2013 Elsevier B.V. All rights reserved.

Prabhu T.R.,Center for Military Airworthiness and Certification | Varma V.K.,Center for Military Airworthiness and Certification | Vedantam S.,Indian Institute of Technology Madras
Journal of Materials Engineering and Performance | Year: 2014

In this work, we studied the high-speed tribological and mechanical properties of layered SiC particulate reinforced iron matrix composites. The layered composites consisted of a surface layer with high volume fraction of the reinforcement particles and a layer with low volume fraction in the bulk. The layered composites are a form of functionally graded materials with high wear resistance near the surface and high thermal conductivity in the bulk. The composites were prepared by standard powder metallurgy techniques. The tribological behavior of the composites was evaluated at 25 to 35 m/s sliding speeds using a sub-scale dynamometer disk brake testing system. The properties of the layered composites were compared to those of uniform composites. The results showed that the layered composites have better wear resistance and braking effectiveness in the range of braking speeds considered. The layered composites also showed higher bending strength than the monolayer composites due to the presence of the interfaces between the layers. © 2014, ASM International.

Ram Prabhu T.,Center for Military Airworthiness and Certification | Varma V.K.,Center for Military Airworthiness and Certification | Vedantam S.,Indian Institute of Technology Madras
Wear | Year: 2014

In this paper, we study the wear resistance of multi-layered composites of Cu/SiC + Gr hybrid composites prepared by layer compaction and pressure sintering. The tribological behavior and wear resistance of the composites were evaluated at a range of sliding speeds (5, 10, 30 and 35m/s) in a laboratory scale inertia brake dynamometer for brake friction material applications. The wear surface morphology and mechanisms were studied using scanning electron microscopy (SEM), XRD, and stereoscopy. The microstructure of the composites was also characterized using SEM and optical microscopy and the mechanical response in compression and flexure was evaluated. The results of these tests indicate that the density, wear resistance, braking behavior and mechanical response can be significantly improved by the presence of a layer of copper away from the sliding surface. The presence of the layer also improved friction and wear resistance significantly. The formation of mechanically mixed tribolayer and oxides (Fe3O4) reduced the wear rate and stabilized the friction coefficient at 30 and 35m/s. Finally, crack deflection and branching at the interface between the composite and Cu layers improved the flexural strength of the layered composites. The fractography analysis indicates a quasi-cleavage intergranular fracture in the composite layer and a purely ductile fracture in the Cu layer. © 2014 Elsevier B.V.

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

In the present study, the effects of solid lubricants, braking load and sliding speed on the tribological behavior of Cu/silica composites were investigated using design of experiments and statistical methods. Three types of composites were prepared using different types of solid lubricants (h-BN, graphite, and MoS2) by powder metallurgy. The wear and friction behavior of the composites were evaluated for a range of braking loads (300, 600, and 900N) and sliding speeds (3, 6, and 9m/s) in a subscale dynamometer. The composites were characterized for density, hardness, microstructure, wear surface morphology and surface roughness properties. A statistical model was developed to identify the significant factors affecting the wear resistance of the composites. The key findings of our study are: (1) MoS2 reinforced composites possess the highest density, densification, hardness, and lowest surface roughness among the composites, (2) MoS2 is the most effective lubricant in improving the wear resistance of the composites for the selected experimental domain, (3) Amongst the solid lubricant, brake load and sliding speed, the solid lubricant is the most significant factor affecting the wear resistance of the composites, (4) graphite reinforced composites provide higher braking performance at 3m/s for all loading conditions whereas both h-BN and MoS2 reinforced composites provide better braking performance among composites at higher speed (>3m/s) and load (>300N) conditions. © 2015 Elsevier Ltd.

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