Regional Center for Military Airworthiness

Bangalore, India

Regional Center for Military Airworthiness

Bangalore, India
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Tumuluri S.,Hindustan Aeronautics Ltd | Murugeshan P.,Hindustan Aeronautics Ltd | Mishra R.K.,Regional Center for Military Airworthiness | Subrahmanyam V.V.,Bangalore University
Journal of Failure Analysis and Prevention | Year: 2017

Direct metal deposition process has been adopted for repair of oil pump gear shaft of an aero engine. The process is first optimized for the specific application of oil pump gear shaft material on a specimen and then the actual part was applied with deposition. The deposition on the gear shaft is validated through stringent quality checks and functionality check of the oil pump during bench test and engine test. The successful adoption of the deposition process is able to prevent failures which would otherwise cause catastrophic failure of the aero engine. Oil pumps are now withdrawn from service at a predetermined time prior to its scheduled inspection and overhaul for application of metal deposition. © 2017 ASM International

Mishra R.K.,Regional Center for Military Airworthiness | Dileep S.,Aerospace Engine Research and Design Center
Journal of Failure Analysis and Prevention | Year: 2017

A novel and highly effective methodology is presented in this study to estimate the stresses and strains and also the life of gas turbine components operating in multiaxial variable amplitude loading conditions. The methodology uses a cyclic plasticity model based on multilinear kinematic hardening (MLKH) for estimation of stress-strain response and Wang and Brown algorithm for counting the reversals in the loading cycle. The stress and strain response extracted for each reversal using the MLKH model where then integrated with multiaxial fatigue damage model based on critical planes (Wang and Brown model) suitable for LCF applications, to predict the fatigue life. The proposed methodology was initially compared with experimental test results of 42CrMo4 low alloy steel specimen, under different loading conditions like proportional, non-proportional and sequential loadings available in the literature. To reinforce the life prediction capability of the methodology, an application level study was undertaken. An air-cooled high-pressure turbine disk of an aero gas turbine engine was used as the model for this study. The fatigue life obtained from the multiaxial fatigue damage model was then compared with the experimental LCF life of the disk obtained from the field data. In order to be conservative in approach, lower bound of the 95% confidence limit of the fatigue data fitted using Weibull probability distribution function was used to compare the numerical life. The study shows a good correlation between the fatigue life arrived experimentally and the predicted life using the proposed methodology. © 2017 ASM International

Shetty B.P.,Nitte Meenakshi Institute of Technology | Reddy S.,Nitte Meenakshi Institute of Technology | Mishra R.K.,Regional Center for Military Airworthiness
Journal of Failure Analysis and Prevention | Year: 2017

The present paper characterizes the structure of 3D model of an aircraft wing leading edge of a passenger aircraft considering GLARE laminates as one of the candidate materials through finite element analysis. The investigation is carried out on different types of GLARE configurations and the results of finite element analysis are well compared analytically with benchmark tests to demonstrate the performance of the modeling technique adopted. The GLARE laminate materials are found suitable for their application in the wing leading edge with some reservation on GLARE 3/2 and GLARE 4/3 for Al alloy 2024-T3 thickness, between 0.2 and 0.4 mm. The finite element approach is able to predict the mechanical behavior of structural elements fast enough so that the results can be incorporated into normal design iteration processes. © 2017 ASM International

Nirmala S.,Regional Center for Military Airworthiness | Ananda C.M.,National Aerospace Laboratories, Bangalore
Proceedings - 2015 International Conference on Cognitive Computing and Information Processing, CCIP 2015 | Year: 2015

Communication in Micro Air Vehicles (MAV) swarm flying is challenging and critical for functional integrity of the swarm network. MAVs are deployed in groups to realise useful applications from MAV. Such mode of deployment of MAVs in-group demands dedicated and well defined communication method, protocol, simplified control and data paths along with the redundancy management to mitigate the failures. On the fly communication failures or complete system failure is addressed by dynamic reconfiguration of fellow MAVs to restructure the network as per Binary Search Tree network (BSTN). BST based network for swarm flying enables simplified and structured network with ordered, dynamic and unique data paths. Reconfiguration of MAV nodes in the BSTN is critical for continued swarm and hence completion of intended function. The paper presents the BST based network for MAVs, communication protocol, metrics for configuration, failure scenarios and redundancy management. © 2015 IEEE.

Mishra R.K.,Regional Center for Military Airworthiness | Kishore Kumar S.,Gas Turbine Research Establishment | Chandel S.,Indian Defence Institute of Advanced Technology
International Journal of Turbo and Jet Engines | Year: 2015

Lean blow out characteristics in a swirl stabilized aero gas turbine combustor have been studied using computational fluid dynamics. For CFD analysis, a 22.5° sector of an annular combustor is modeled using unstructured tetrahedral meshes comprising 1.2×106 elements. The governing equations are solved using the eddy dissipation combustion model in CFX. The primary combustion zone is analyzed by considering it as a well stirred reactor. The analysis has been carried out for different operating conditions of the reactants entering into the control volume. The results are treated as the base-line or reference values. Combustion lean blow-out limits are further characterized studying the behavior of combustion zone during transient engine operation. The validity of the computational study has been established by experimental study on a full-scale annular combustor in an air flow test facility that is capable of simulating different conditions at combustor inlet. The experimental result is in a good agreement with the analytical predictions. Upon increasing the combustor mass flow, the lean blow out limit increases, i.e., the blow out occurs at higher fuel-air ratios. In addition, when the operating pressure decreases, the lean blow out limit increases, i.e., blow out occurs at higher fuel-air ratios. © 2015 by De Gruyter.

Kale S.S.,Regional Center for Military Airworthiness Foundry and oForge | Raja V.S.,Indian Institute of Technology Bombay | Bakare A.K.,Regional Center for Military Airworthiness
Corrosion Science | Year: 2013

Studies were conducted to investigate the effect of polymer matrix composite stiffener (patch) on environmentally assisted cracking (EAC) susceptibility of pre-cracked alclad Al-Zn-Mg-Cu-Cr alloy in 3.5wt.% NaCl environment. The EAC threshold stress intensity of the peak and two-step aged alloy was reduced from 26 to 7MPam1/2 and 31to 8MPam1/2 respectively under the influence of patch. The plateau crack velocity was increased from 2.5×10-9 to 5.1×10-9m/s for peak aged and 1.2×10-9 to 2.0×10-9m/s for two-step aged tempers in patched condition. The significant increase in EAC susceptibility was attributed to crevice effect generated by the stiffener. © 2013 Elsevier Ltd.

Kale S.S.,Regional Center for Military Airworthiness Foundry and Forge | Raja V.S.,Indian Institute of Technology Bombay | Bakare A.K.,Regional Center for Military Airworthiness
Corrosion Engineering Science and Technology | Year: 2014

Stiffening of Al alloy aircraft structures with carbon fibre reinforced plastic laminate called 'patches' is considered as a viable option to enhance fatigue life. Interface so created between the reinforcement and Al alloy structure is potential site for crevice corrosion attack. Therefore, studies were conducted to investigate the interface corrosion behaviour of peak and two-step aged Al-Zn-Mg-Cu-Cr alclad alloy with and without the patch and examine the possibility to control the interfacial attack with the addition of cerium chloride inhibitor exposed to 3.5 wt-% NaCl solution for the durations of 2 and 168 h. Electrochemical impedance spectroscopy revealed that the interface attack was significantly reduced by the addition of 1000 ppm cerium chloride. The response of the peak and two-step aged alloy for such an addition was further investigated and found that the alloy under step aged condition behaves better than that of the peak aged condition.©2014 Institute of Materials, Minerals and Mining.

Mishra R.K.,Regional Center for Military Airworthiness | Srinivasan K.,Hindustan Aeronautics Ltd
Journal of Failure Analysis and Prevention | Year: 2016

Failure of low-pressure (LP) turbine rotor blades in low bypass military turbofan engines is a great concern for designers, manufactures, repair and overhaul agencies, operators, and airworthiness authorities. The present paper analyzes the LP turbine blade failure cases to determine its root cause. Forensic and metallurgical investigations are carried out on the failed blades. In most cases, the failure was originated from the leading edge and had propagated toward the trailing edge. Intergranular features and high oxidation on the fractured surface have been found as the cause of fatigue failure. Operation at elevated temperatures for considerable time was found responsible for these fatigue failures. Malfunction of fuel system, failure in control sensors, and nonuniformity in atomizer characteristics were the root cause of high temperature in turbine leading to the failure of blades. The paper also presents various remedial measures to address the blade failures from manufacturing and operational points of view. © 2016, ASM International.

Sahoo B.,Regional Center for Military Airworthiness | Satpathy R.K.,Regional Center for Military Airworthiness | Panigrahi S.K.,Indian Defence Institute of Advanced Technology
International Journal of Turbo and Jet Engines | Year: 2016

This paper deals with failure analysis of a low-pressure turbine blade of a straight flow turbojet engine. The blade is made of a wrought precipitation hardened Nickel base superalloy with oxidation-resistant diffusion aluminizing coating. The failure mode is found to be fatigue with multiple cracks inside the blade having crack origin at metal carbides. In addition to the damage in the coating, carbide banding has been observed in few blades. Carbide banding may be defined as inclusions in the form of highly elongated along deformation direction. The size, shape and banding of carbides and their location critically affect the failure of blades. Carbon content needs to be optimized to reduce interdendritic segregation and thereby provide improved fatigue and stress rupture life. Hence, optimization of size, shape and distribution of carbides in the billet and forging parameters during manufacturing of blade play a vital role to eliminate/reduce extent of banding. Reference micrographs as acceptance criteria are essential for evaluation of raw material and blade. There is a need to define the acceptance criteria for carbide bandings and introduce more sensitive ultrasonic check during billet and on finished blade inspection. © 2016 by De Gruyter.

Mishra R.K.,Regional Center for Military Airworthiness | Ahmed S.I.,ORDAQA Engines | Srinivasan K.,Hindustan Aeronautics Ltd Engine Division
Journal of Failure Analysis and Prevention | Year: 2013

This paper investigates a bird strike incident of a military gas turbine engine. The jet pipe temperature of the engine shoot up and rotor speed reduced suddenly during takeoff roll. Long flame was noticed from the engine and aircraft crashed at runway end. Forensic analysis of remnants collected from flow passages confirmed the bird ingestion. Blockage of flow passages due to the presence of bird has led to engine surge and high gas temperature resulting in extensive damage of low pressure turbine module. The paper also proposes remedial measures to avoid such bird strikes during flight. © 2013 ASM International.

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