Showing papers by "Defence Research and Development Laboratory published in 2020"

Micro-machining through electrochemical discharge processes: a review

Abstract: The present study reviews the state-of-the-art mechanism for the generation of spark by means of micro-electrochemical discharge machining (µ-ECDM) process. It also describes various electr...

Electron-beam welding of high-entropy alloy and stainless steel: microstructure and mechanical properties

Abstract: An autogenously dissimilar Al0.1CoCrFeNi-high entropy alloy/stainless steel (i.e., AISI 304) weld joint was produced by an electron-beam welding technique. The weld metal followed mode A of solidif...

COVSACK: an innovative portable isolated and safe COVID-19 sample collection kiosk with automatic disinfection

Abstract: The Corona VIrus Disease 2019 (COVID-19) is one of the significant medical disaster that changed the life of humankind in the 21st century The deadly virus is transmittable from infected person, through his nasal droplets, to surrounding people among whom, the healthcare personnel are the utmost affected The present article brings out an innovative chamber, which is used for collection of throat, or nasal swabs/samples for diagnosis of COVID-19 suspected persons The chamber, called COVid SAmple Collection Kiosk (COVSACK), eliminates the transmission of the deadly virus to the health care personnel while collecting the sample The kiosk is designed based on CFD simulations for effective spread of disinfectant in fine droplet form, built with a lightweight composite that is sustainable in extreme weather conditions and the kiosk can be easily sanitized within 3 min after sample collection The chamber is first positioned in ESI Hospital, Hyderabad, and other hospitals and diagnostics centres across India, extensively being used for testing the COVID-19 patients at a faster rate, with a drastic reduction in use of personal protection equipment (PPE) This technological innovation, to certain extent, has changed the way the testing of COVID-19 patients carried out in the country

Forward and reverse modelling of flow forming of solution annealed H30 aluminium tubes

Abstract: Modelling of flow forming of tube-shaped solution annealed H30 Aluminium alloy is considered in the present study. Initially, a total of 136 experiments have been conducted to realize the process and subsequently influences of three inputs (feed–speed ratio, roller infeed and axial stagger) on the three outputs, viz. internal diameter, springback and ovality have been studied. Three neural network-based approaches (back-propagation neural network, limited-memory BFGS network and genetic neural system) have been developed for forward as well as reverse modelling of the process. During forward modelling, the performances of the three neural network-based approaches have been compared with the regression model. It is seen that GANN has performed much better compared to the other methods. Percentage accuracy in predicting ovality using regression analysis is the worst, and it necessitates consideration of more input process parameters for better prediction accuracy. However, NN-based approaches adapted such cases well. Comparison of all the three NN-based approaches among themselves has been made during reverse modelling. During this process, prediction accuracy, using LBFGSNN, is found to be better than the other two methods. Thus, it is perceived that NN-based models might suit better for prediction of shape accuracy of flow-formed shell.

Thermal Design Methodology for Regenerative Fuel-Cooled Scramjet Engine Walls

Abstract: Thermal protection of scramjet engine combustor wall for long-duration operation is one of the major challenges. Regenerative cooling of the combustor walls using hydrocarbon fuel as a coolant is one of the best solutions to withstand high heat transfer rates for the long duration application. In such a case, before embarking on materials development and fabrication, it would be most beneficial to have a procedure that simultaneously selects the preferred material and design. Thermal design methodology of regenerative cooling system for hydrocarbon fueled air-breathing engine walls is presented in this paper. The main ingredient is three-dimensional heat transfer analysis coupled with fluid flow based on FEM that can be used for the thermal management study of regenerative cooled panel configurations and selection of materials including Thermal Barrier Coatings (TBCs). The procedure is applied for the thermal design of fuel-cooled scramjet combustor walls exploiting physical heat sink of hydrocarbon fuel. High-temperature materials, viz., Cb-752, C-103, and C-SiC are considered as the candidate materials along with TBC. Results of the analysis carried out for several combinations of material of construction, TBC with suitable bond coat material, wall thickness, and channel location are presented. It is inferred that TBC along with regenerative cooling is playing a major role in reducing the engine wall temperature thereby maintaining the fuel temperature inside the channels within desirable limit. The Cb-752 material coated with Y2O3 TBC remains viable solution for thermal management of scramjet engine walls for the long-duration application.

CFD Methods in High-Speed Airbreathing Missile Propulsion Design

Abstract: Application of CFD tools in the design and analysis of high-speed airbreathing systems is described. Three-dimensional Navier-Stokes equations are solved along with SST-k-ω turbulence model. Lagrangian particle tracking method for kerosene droplet and single-step chemical reaction based on fast chemistry is used to model kerosene–air reaction. The computational tool is extensively validated against reliable experimental data before applying to design exercise. Better insight obtained from numerical simulations about the mixing and combustion process inside the combustor has enabled the placement of fuel injection struts and the injectors to obtain optimized combustor performance and benign thermal environments for a flight-sized hydrocarbon-fuelled scramjet combustor. Computed wall pressure matches nicely with experimental data for both non-reacting and reacting flows. Computed convective heat flux obtained through well-resolved thermal boundary layer simulations is used in the thermo-structural analysis of the scramjet combustor. End-to-end simulations integrating both external (non-reacting) and internal (reacting) flow are carried out of a complete hypersonic airbreathing vehicle to obtain complete aerodynamics and propulsion parameters of the vehicle for mission design. The evaluated installed air intake performance in terms of pressure recovery and mass capture ratio matches very well with experimental data. For higher angles of attack, windward and leeward side intakes show different performances, and leeward side intake experiences subcritical operation faster. The interaction between forebody boundary layer and intake shock system causes significant spillage. The starting and unstarting characteristics of a hypersonic intake are evaluated through unsteady RANS simulations. Both started flow and unstarted flow with large pressure oscillation are captured for different Mach numbers. The use of CFD tools has reduced the dependence of experimental testing in the design of high-speed airbreathing Propulsion Systems.

Microstructures and Mechanical Properties of Dissimilar Metal Gas Tungsten Arc Welds of 15CDV6 Steel and AISI 304 Stainless Steel

Abstract: The pressure pipeline applications demand high strength steels and stainless steels based on the requirement of strength and corrosion point of view, respectively Welding is one of the widely practiced metal joining techniques in such kind of applications due to the high-pressure environment The present work is primarily aimed at understanding the feasibility and producing X-ray radiography quality gas tungsten arc welds of dissimilar steels, particularly, 15CDV6 steel and AISI 304 stainless steel The sound dissimilar GTA welds are subjected to evaluation of microstructures, mechanical properties such as microhardness across the weldment and tensile properties The mechanical properties are further correlated to microstructures of dissimilar weld joints The filler wire material has profound influence on the microstructures and mechanical properties (both tensile strength and hardness) of dissimilar steel weld joints The dissimilar weld made with 8CD12 filler wire demonstrated higher tensile strength and joint efficiency as compared to the dissimilar weld made with ER 308L filler wire

Estimation of the Grain Size Number and Microstructure Analysis of AA6061 Alloy Flow Formed Tubes

Abstract: Flow forming process is a chipless metal forming process used for the production of high accuracy axi-symmetrical cylindrical components. During this process there is an increase in tube length and decrease in thickness without any change in internal diameter. Generally forming is performed with a single roller or three rollers over a rotating mandrel and the present work is with three roller setup. The work material is plastically deformed in the radial direction by compression due the rollers and made to flow in an axial direction and the thickness reduction is achieved with single pass. The AA6061 aluminum alloy, usually used in defense components is considered for flow forming. The mechanical properties of this alloy are dependent on the rate at which the alloy is heated and quenched. Solution treatment has been carried out at 400 °C for 2 h followed by quenching in water. Microstructure of the finished product has been studied by using SEM and grain size is estimated for different reduction ratios and stagger distance using the intercept method.

Analysis of Characteristics of Launcher Missile System and Its Optimization to Reduce Tip-Off Effect During Launch

Abstract: This paper focuses on analyzing the motion characteristics of the launcher missile system and locations of interactions between missile shoes and launch rail. The deviation of direction of the thrust force from flight axis of the missile is known as thrust misalignment. And the deviation of direction of the missile is known as tipoff rate. The main objective of this paper is to analyze characteristics of launcher missile system and its optimization to reduce tipoff rate. The analysis is performed by modeling and simulating the launcher missile system using CAD package and ADAMS software.

Thermal Design and Testing of External Protuberance of Hypersonic Carrier Vehicle Airframe

Abstract: Hypersonic carrier vehicle airframe experiences high rate of heat transfer caused by aerodynamic heating due to very high-speed flow during flight. A wire tunnel over the carrier vehicle is used to accommodate the communication and electric cables routed along the external surface of rocket motor casing from electronics packages section to rear part of the carrier vehicle. The wire tunnel leading edge forms an external protuberance. The protuberances are subjected to severe heating during the flight, especially at hypersonic speed. Thermal design of the protuberance structure is imperative to ensure safe operation in the severe thermal environment experienced during flight. This paper describes the thermal design of wire tunnel protuberance. Further, the design of wire tunnel assembly is ascertained by thermal test conducted in the infrared heating facility for aerodynamic heating condition corresponding to the flight trajectory.

Design of Fixture for Trimming of a Composite Material Shim by Abrasive Water Jet Machining

Abstract: The fixtures required in manufacturing must correctly locate workpiece in a given orientation with respect to cutting tool. The present work aims at design of fixture for trimming of a component called shim which is made of composite material. The trimming is done by abrasive water jet machine. Machining by conventional methods compromise the strength of the composite materials and/or cause delamination, making it less suitable for aerospace applications, thus Abrasive Water Jet (AWJ) technology is used for machining composite materials. In present work, the shim made of composite material is required to be cut at specified orientation at given location in a circular path. Since the shim is a thin-walled structure, excess clamping force may deform it and it may not get cut at required positions, although sufficient support and clamping is required to hold the component during trimming operation by water jet machining. The fixture needs to be designed for an abrasive water jet machine in which the water jet nozzle head is stationary and automation, e.g., rotary table is not available for maintaining circular cut at specified location and orientation. A fixture is designed to meet the above requirements. The suitable rotational speed to cut the shim is found experimentally and the shim is cut in circular path at desired location on the fixture.

Development of Alignment Fixture for Precision Assembly of Aerospace Control Surfaces Incorporating Process and Assembly Variations

Abstract: Actuator alignment is crucial and of paramount importance in meeting high precision pointing and reliable control performance of Aerospace vehicle emission requirements. In this paper, a holistic approach has been made for precise alignment of the Aerospace control surfaces with the actuators through the development of an Assembly Fixture with the help of CAD software taking into account variations in fabrication and assembly for meeting the stringent specification requirements. The Assembly Fixture resulted in reduction of lead time for 3D inspection and also ensured repeatable functional performance of the actuator assembly.

Studies on thermal stability and life estimation of epoxy adhesive by thermogravimetric analysis for high-temperature applications

Abstract: Structural epoxy adhesive was investigated for its thermal stability and degradation behaviour in a thermo-oxidative environment by thermogravimetry analysis (TGA). Non-isothermal TGA was performed at temperatures between 30 and 600°C utilizing different heating rates. The ageing characteristics of material were determined by an accelerated ageing study using isothermal TGA at different temperatures for 5% threshold conversion. The activation energies from both non-isothermal TGA and isothermal TGA were estimated and the activation energy values for 5% degradation from both the methods were in good agreement. The epoxy adhesive with titanium dioxide as filler showed a shelf life exceeding 13 years at ambient conditions (27°C). Additionally, the lap shear strength of the adhesive joint was also tested after treating the samples at 70°C with 90% relative humidity to evaluate the hydrothermal effect on adhesive joint.

Fiber Laser Cutting of Nimonic C263 Alloy and Investigation of Surface Integrity

Abstract: Nimonic C263 is a super alloy which contains more than 50% nickel, and is mainly used in gas turbines and internal combustion engines. The present study deals with the fiber laser cutting of Nimonic C263 super alloy using nitrogen as assisting gas. Several experiments were performed by varying the process parameters, such as cutting speed, laser power, gas pressure, position of focus point with respect to the top surface of the workpiece and duty cycle, to observe their influences on the cut-surface integrity. The prepared samples were characterized by FESEM examination, microhardness test, optical microscopy and XRD technique. The average kerf width, heat-affected zone and surface roughness values varied from 201 to 261 µm, 7.96 to 9.30 µm and 2.02 to 3.42 µm.