Showing papers by "Defence Research and Development Laboratory published in 2018"
TL;DR: In this paper, Artificial Neural Network (ANN) was used to model the relationship between the input parameters and the mechanical and corrosion properties (output) of the weld joints to obtain defect free weld joint with maximum weld strength.
Abstract: In this paper, parameter optimization of FSW of cryorolled AA2219 alloy was carried out to obtain defect free weld joint with maximum weld strength. To achieve this, artificial neural network (ANN) was used to model the relationship between the input parameters and the mechanical and corrosion properties (output) of the weld joints. The optimal FSW parameters were determined by genetic algorithm (GA). The feasible solution of the GA was tool rotational speed of 1005 rpm, tool travel speed of 20 mm/min and tool tilt angle of 3°. The feasible parameter was used to weld and check the ability of the parameter to produce better weld joint than the L9 orthogonal array parameters. The weld, subjected to the confirmation test, was investigated by means of metallurgical, mechanical, and corrosion testing. This process reduces the costs associated with trial runs to obtain optimal parameters and also the production cost of the cryorolled (CR) plate which is high.
65 citations
TL;DR: In this paper, three layers of stack was used for bonding of multilayered composite and preheated at 250 °C for 20 min, and the effects of rolling parameters on bond strength and deformation of the strips were analyzed.
Abstract: In the present study commercially pure magnesium and aluminum strips were fabricated using the process of accumulative roll bonding. It is a prominent solid state joining process to manufacture similar and dissimilar materials for various applications. Three layers of stack was used for bonding of multilayered composite and preheated at 250 °C for 20 min. The effects of rolling parameters on bond strength and deformation of the strips were analyzed. The interface between aluminum and magnesium were characterized to identify the formation of diffusion compounds, and are found to be the presence of Al12Mg17 intermetallic compounds. Tensile strength of the bonds was increased with the decreasing of thickness of the strips. The interface characteristics were analyzed using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDAX) to reveal the intermetallic compounds, micro cracks and bonding properties. The strength of the composites is varying with width of the intermediate strip and maximum strength values were obtained after three passes of the roll bonding.
43 citations
01 Mar 2018
38 citations
01 Mar 2018
TL;DR: In this paper, the interface microstructure formation between filler metal and substrates, and spreading of the filler metal were studied, and the micro hardness at the weld interfaces was found to be higher than the substrates owing to the presence of Fe2Al5 and CuAl2 intermetallic compounds.
Abstract: The dissimilar joining using gas tungsten arc welding - brazing of 304 stainless steel to 5083 Al alloy had been conducted with the addition of Al-Cu eutectic filler metal. The interface microstructure formation between filler metal and substrates, and spreading of the filler metal were studied. The interface microstructure between filler metal and aluminum alloy characterized that the formation of pores and elongated grains with the initiation of micro cracks. The spreading of the liquid braze filler on stainless steel side packed the edges and appeared as convex shape, whereas a concave shape has been formed on aluminum side. The major compounds formed at the fusion zone interface were determined by using X-ray diffraction techniques and energy-dispersive X-ray spectroscopy analysis. The micro hardness at the weld interfaces found to be higher than the substrates owing to the presence of Fe2Al5 and CuAl2 intermetallic compounds. The maximum tensile strength of the weld joints was about 95 MPa, and the tensile fracture occurred at heat affected zone on weak material of the aluminum side and/or at stainless steel/weld seam interface along intermetallic layer. The interface formation and its effect on mechanical properties of the welds during gas tungsten arc welding-brazing has been discussed.
34 citations
TL;DR: In this paper, a mathematical model of tensile braking load as a function of geometrical attributes of weld bead geometry is presented, which suggests the effective thickness of weld has the most significant influence on tensile breaking load of dissimilar weld joint.
32 citations
TL;DR: In this paper, a hybrid pin profiled tool that enables sound welds at speeds 7-times faster than a conventional tool (a conical threaded tool), without pin breakage is presented.
21 citations
TL;DR: The present proposed approach replaces the existing practice of physical search for tools from the databooks/tool catalogues with intelligent knowledge-based selection system that employs artificial intelligence based techniques such as artificial neural networks, fuzzy logic and genetic algorithm for decision making and optimization.
Abstract: With the increased trend in automation of modern manufacturing industry, the human intervention in routine, repetitive and data specific activities of manufacturing is greatly reduced. In this paper, an attempt has been made to reduce the human intervention in selection of optimal cutting tool and process parameters for metal cutting applications, using Artificial Intelligence techniques. Generally, the selection of appropriate cutting tool and parameters in metal cutting is carried out by experienced technician/cutting tool expert based on his knowledge base or extensive search from huge cutting tool database. The present proposed approach replaces the existing practice of physical search for tools from the databooks/tool catalogues with intelligent knowledge-based selection system. This system employs artificial intelligence based techniques such as artificial neural networks, fuzzy logic and genetic algorithm for decision making and optimization. This intelligence based optimal tool selection strategy is developed using Mathworks Matlab Version 7.11.0 and implemented. The cutting tool database was obtained from the tool catalogues of different tool manufacturers. This paper discusses in detail, the methodology and strategies employed for selection of appropriate cutting tool and optimization of process parameters based on multi-objective optimization criteria considering material removal rate, tool life and tool cost.
19 citations
TL;DR: It is brought out that the pattern search algorithm offers superior performance in comparison with the genetic algorithm for this class of optimization problem and offers a viable tool for optimizing trajectories for the considered class of vehicles.
Abstract: In this work, trajectory optimization of an aerodynamically controlled hypersonic boost glide class of flight vehicle is presented. In order to meet the mission constraints such as controllability, skin temperature, and terminal conditions etc., the trajectory is optimized using a pattern search algorithm with the lift to drag (L/D) ratio as a control parameter. It is brought out that the approach offers a viable tool for optimizing trajectories for the considered class of vehicles. Further, the effects of the constraints on trajectory shape and performance are studied and the analysis is used to bring out an optimal vehicle configuration at the initial stage of the design process itself. The research also reveals that the pattern search algorithm offers superior performance in comparison with the genetic algorithm for this class of optimization problem.
15 citations
01 Jun 2018
14 citations
TL;DR: Flow forming is an innovative form of cold and chipless metal forming process, used for the production of high precision, thin-walled, net-shaped cylindrical components as mentioned in this paper.
Abstract: Flow forming is an innovative form of cold and chipless metal forming process, used for the production of high precision, thin-walled, net-shaped cylindrical components. During this process, the length of a thick walled tube, commonly known as a preform, is increased with a simultaneous decrease in the thickness of the preform without any change in the internal diameter.
Forming of the preform is carried out with the help of one or more rollers over a rotating mandrel. By a pre-determined amount of thickness reduction in one or more number of forming passes, the work material is plastically deformed in the radial direction by compression and made to flow in an axial direction. The desired geometry of the workpiece is achieved when the outer diameter and the wall of the preform are decreased, and the available material volume is forced to flow longitudinally over the mandrel. Over the last three and a half decades the flow forming technology has undergone several remarkable advancements. The versatility of the process makes it possible to produce a wide variety of axi-symmetric, nearer to the net-shape tubular parts with a complex profile using minimum tooling changes. In this review article, process details of flow forming have been elaborated. The current state-of-the-art process has been described, and future developments regarding research and industrial applications are also reviewed.
13 citations
TL;DR: In this article, a finite element (FE) approach was adopted to determine the coefficient of friction at tool chip interface to obtain rational values of cutting force for the identified cutting range.
TL;DR: A detailed investigation on the formation of θ′ and θ″ precipitates in the Cryorolled (CR) material of AA 2219 alloy and the Friction Stir (FS) welded portion of CR AA2219 and their influence on material characterizations is presented in this paper.
TL;DR: Abrasive water jet machining (AWJM) is a non-conventional material removal process as discussed by the authors, which is superior to any other cutting techniques for processing various materials, particularly in processing difficult to cut materials.
TL;DR: This letter considers simultaneous primary user (PU) detection and channel estimation for censoring-based spectrum sensing in cognitive radio networks over fading channels and optimize the censoring parameter and the power allocation for throughput maximization under transmit and interference power constraints.
Abstract: This letter considers simultaneous primary user (PU) detection and channel estimation for censoring-based spectrum sensing in cognitive radio networks over fading channels. We formulate the problem mathematically for Rician and Rayleigh fading channels. Closed-form expressions are derived for the critical performance metrics in low SNR regime. Further, we optimize the censoring parameter and the power allocation for throughput maximization under transmit and interference power constraints. Our results demonstrate that simultaneous PU detection and channel estimation substantially improve the throughput of cognitive radio networks over an approach where PU detection and channel estimation are treated independently.
TL;DR: In this paper, the effect of aluminum addition on the micro structural, corrosion and mechanical properties of Al x CoCuFeNiTi (x = 0, 0.75, 1 atom %) High Entropy Alloys which were prepared by Arc melting route.
TL;DR: In this article, large eddy simulations of subsonic and supersonic boundary layers separating at backward facing steps are performed for validating a hybrid flow solver and testing the digital filtering approach for specifying the inflow turbulence.
Abstract: Large eddy simulations (LES) of subsonic and supersonic boundary layers separating at backward facing steps are performed for validating a hybrid flow solver and testing the digital filtering approach for specifying the inflow turbulence. The broadband spectra of eddies in the approaching boundary layers resulting from filtering properly trigger the shear layer instabilities leading to significant improvements in predictions of first and second order turbulence statistics when compared to those resulting from use of uncorrelated noise for generating inflow turbulence. This seems to be true even though the distance between the inflow boundary and the step is about the same or less than in most of the LES of this kind of flows reported in literature and not sufficient to establish an equilibrium boundary layer with correct phase information before the flow reaches the step. The density/entropy disturbances resulting from non-solenoidal inflow do not seem to adversely affect the predictions in the subsonic case. The digital filtering approach does, however, generate acoustic disturbances that contaminate the expansion fan generated at the corner and lead to slight overpredictions in turbulence levels downstream in the supersonic case.
TL;DR: In this article, the authors brought out the unique application of ultrasonic based thickness gauge and a practical approach made in thickness measurement of typical rocket motor casings, which is a critical parameter and plays an important role in performance of the aerospace vehicle.
01 Apr 2018
TL;DR: This work proposes a trajectory optimization formulation for hypersonic boost–glide class vehicles to achieve maximum range under various in-flight and terminal constraints and addresses the requirement of a certain minimum dynamic pressure to ensure aerodynamic controllability throughout the flight envelope for various ranges.
Abstract: In this work, a trajectory optimization formulation for hypersonic boost–glide class vehicles to achieve maximum range under various in-flight and terminal constraints is proposed. While most of th...
TL;DR: A polynomial based guidance law dependent on range-to-go, is proposed for interception of a non-maneuvering moving target, by a dual-seeker interceptor, and simulation results show the efficacy of the guidance law.
TL;DR: In this article, the authors developed novel glass fabric-reinforced polybenzoxazine-silicate composites with enhanced performances by copolymerization of bisphenol F benzoxazine using glass fabric, polyvinyl butyral as the coupling agent and various ratios of ethyl silicate.
Abstract: The aim of this study is to develop novel glass fabric-reinforced polybenzoxazine–silicate composites with enhanced performances, which can overcome the disadvantages related to the low crosslink density of glass fabric-reinforced polybenzoxazine composites. Glass polybenzoxazine silicate composites were prepared via the copolymerization of bisphenol F benzoxazine using glass fabric, polyvinyl butyral as the coupling agent and various ratios of ethyl silicate. FTIR and DSC were utilized to study the chemical reactions and curing optimization, respectively. It was found that complete polymerization occurred at 200 °C. DMA analysis of the prepared glass polybenzoxazine silicate composites showed enhanced stiffness, crosslink density, service temperature, and network branching with uniform phase distribution. The thermal oxidative decomposition temperatures and char yield obtained by TGA and interfacial adhesion by SEM for glass polybenzoxazine silicate composites were found to be improved when compared to that of the glass polybenzoxazine composites. The composites prepared by this method showed enhanced service temperature, stiffness, crosslink density, thermal oxidative resistance, and char yield when compared to glass fabric-reinforced homopolymerized polybenzoxazine composites. These newly developed glass polybenzoxazine silicate composites are promising materials to overcome various shortcomings associated with polybenzoxazine and other traditional resin composites.
TL;DR: In this paper, a mathematical model was developed considering pipe of uniform c/s and moving liquid-gas interface, and experimental studies have been done using water as working medium instead of actual propellant.
TL;DR: In this article, the influence of heat input on microstructure, microhardness, and mechanical properties of welded structures of DP 590 (Commercially known as DP 600 grade) grade steel of 1.6 mm thickness sheet was investigated.
TL;DR: In this paper, the FSW was carried out with pairs of 6 mm thick CR aluminium plates with different tool pin profiles and the results of the mechanical analysis revealed that the joint made by the hexagonal pin tool had good strength compared to other pin profiles.
Abstract: Friction stir welding (FSW) process was conducted on cryorolled (CR) AA2219 plate using different tool pin profiles such as cylindrical pin, threaded cylindrical pin, square pin and hexagonal pin profiles. The FSW was carried out with pairs of 6 mm thick CR aluminium plates with different tool pin profiles. The different tool pin profile weld portions' behaviors like mechanical (tensile strength, impact and hardness) and metallurgical characteristics were analyzed. The results of the mechanical analysis revealed that the joint made by the hexagonal pin tool had good strength compared to other pin profiles. This was due to the pulsating action and material flow of the tool resulting in dynamic recrystallization in the weld zone. This was confirmed by the ultra fine grain structure formation in Weld Nugget (WN) of hexagonal pin tool joint with a higher percentage of precipitate dissolution. The fractograph of the hexagonal tool pin weld portion confirmed the finer dimple structure morphology without having any interior defect compared to other tool pin profiles. The lowest weld joint strength was obtained from cylindrical pin profile weld joint due to insufficient material flow during welding. The Transmission Electron Microscope and EDX analysis showed the dissolution of the metastable θ ″, θ ′ (Al2 Cu) partial precipitates in the WN and proved the influence of metastable precipitates on enhancement of mechanical behavior of weld. The XRD results also confirmed the Al2 Cu precipitation dissolution in the weld zone.
TL;DR: In this paper, an ideal magnetohydrodynamics (MHD) solver for finite volume flows has been proposed, which is able to simulate the complex flows due to MHD interactions.
Abstract: This paper presents the baseline development of an ideal magnetohydrodynamics (MHD) solver towards enhancing the knowledge base on the numerical and flow physics complexities associated with MHD flows. The ideal MHD governing equations consisting of the coupled fluid flow equations and the Maxwell’s equations of electrodynamics are implemented in the three dimensional finite volume flowsolver, CERANS. Upwind flux functions such as AUSM-PW+, KFVS and the local Lax-Friedrichs schemes were used for solving the discretized form of governing equations. The solenoidal constraint which requires that the magnetic field to be divergence free all through the flow field evolution is ensured using the artificial compressibility analogy method or the Powell’s source term method. The code had been validated for standard MHD test cases involving complex flowfields such as the MHD shock tube, blast, vortex, cloud-shock interaction and cylinder shock interaction problems. The flow control effect of MHD interaction had been demonstrated for supersonic flow past a wedge and the results are compared with analytical results obtained by solving the MHD Rankine Hugoniot relations. Further, MHD flow control for high speed flows had been demonstrated for the hypersonic blunt body problem. Through rigorous testing and validation, it is observed that the CERANS-MHD code is able to mimic the complex flows due to MHD interactions and the comparison of results are found to be in good agreement with similar literature.
TL;DR: A novel formulation is presented for synthesizing optimal trajectory for interceptor of a hostile maneuvering target under an overbearing set of constraints using Evolutionary Optimization techniques.
TL;DR: In this article, three dimensional Reynolds-Averaged Navier Stokes equations along with turbulence models are solved to find the effect of transverse sonic slot injection into a supersonic flow.
Abstract: The knowledge of transverse sonic injection flow field is very important for the design of scramjet combustor. Three dimensional Reynolds-Averaged Navier Stokes equations alongwith turbulence models are solved to find the effect of transverse sonic slot injection into a supersonic flow. Grid sensitivity of the results is studied for various structured grids. Simulations with different turbulence models (i.e., k-e, k-ω, SST-kω, and RNG-ke) reveals that RNG-ke turbulence model better predicts the flow features. Computational fluid dynamics predicted wall pressure distribution for various injection pressures matches well with experimental data. The extent of upstream separated region increases with the increase of the injection pressure. The increase of slot width makes the interaction between transverse jet and free stream more intense and causes more spreading and penetration of injectant in the downstream region.
01 Jan 2018
TL;DR: This study investigates use of genetic algorithms (GA) as an optimization procedure in the flight trajectory planner to be used in the real-time environment.
Abstract: Mission planning is a critical stage in launching a cruise missile against highly defended targets It is required to generate an optimal trajectory during combat scenario (real time) just before launch Typically, this type of engagement is carried by cruise missiles flying at low altitudes below 100 m In addition to air defense, terrain features also need to be avoided by following certain way-points This study investigates use of genetic algorithms (GA) as an optimization procedure in the flight trajectory planner to be used in the real-time environment
TL;DR: The proposed framework has been used to design the heater for one of the known published data and it is found that the predicted performance of RSH is in good agreement with the published data, establishing the accuracy of the developed framework.
TL;DR: The paper addresses and solves the guidance loop stability problem arising due to body rate coupling to the seeker, which becomes acute due to fast guidance time constant and higher subsystem BW required in order satisfying very stringent mission requirement.
TL;DR: In this article, the authors presented the development of a Finite Element model of a contoured composite panel with co-cured stiffeners using ANSYS 15.0, and the response of the panel is observed for variation in stresses, deflections and failure criteria.
Abstract: Composite materials are emerging to be the best applied materials for aerospace applications. With rapid improvement in computational facilities, it is now possible to design the best composite lay up for a particular kind of application. This paper presents the development of a Finite Element model of a contoured composite panel with co-cured stiffeners using Finite Element Simulation. Commercial package ANSYS 15.0 is used for this study. Such half contoured panels find wide application in Aerospace industry. The panel is hinged at one of the ends and dynamically loaded at the other end over a relatively small surface area by transverse load. The response of the panel is observed for variation in stresses, deflections and failure criteria. The panel is expected to rotate about the hinge point by 4° from the initial point. The transient response of the composite panel has been observed for expected load and two test load cases and results reported in this paper. Analysis has become useful input for the design of panel.