Showing papers by "Defence Research and Development Laboratory published in 2017"

Prediction and optimization of weld bead geometry for electron beam welding of AISI 304 stainless steel

Abstract: Electron beam welding, though considered a sophisticated welding process, still requires the operator to first carry out several trial welds to find the right combination of welding parameters based on intuition and experience. This archaic method is often unreliable, leading to unproductive manufacturing lead time, man hours, quality control tests, and material wastage. The current study eliminates this “trial and error” method by providing a reliable model which can predict the right combination of weld parameters to achieve a high-quality weld. Beads on plate welds were carried out on AISI 304 stainless steel plates using a low-kilovolt electron beam welding (EBW) machine. A model that can predict weld bead geometry and provide optimized output for minimum weld area condition without compromising on weld quality was developed. Experimental data were collected as per full factorial design of experiments, and the levels for each input parameter were established through pilot experiments. A multivariate regression analysis has been conducted to establish a relationship between four weld input parameters (three levels each) and four weld bead responses. Response surface methodology (RSM) has been used to study the interrelationship between input parameters and their effect on each response variable. Further, minimization of weld cross-sectional area was done using genetic algorithm for maximum penetration and minimum weld area condition. The optimized mathematical model convincingly establishes that the focusing current is a significant input parameter with very high influence over the weld bead geometry. Extensive material characterization and mechanical tests have been carried out to validate the regressed input-output relationship and the optimized mathematical model.

Thermo-mechanical characterization of laser textured LaMgAl11O19/YSZ functionally graded thermal barrier coating

Abstract: The ablation resistance and adhesion strength of laser textured and as-sprayed functionally graded LaMgAl 11 O 19 /YSZ based thermal barrier coating (FG-TBC) was studied and compared with a duplex coating of LaMgAl 11 O 19 and YSZ (DC-TBC). The thermal barrier coatings were sprayed over Hastelloy C263 using atmospheric plasma spray process (APS). The laser texturing was performed using a picosecond pulsed laser. The width-to-depth ratio and groove spacing were varied to analyse and correlate the significance of groove parameters in providing strain tolerance under extreme thermal loading conditions. The ablation behaviour of the coatings was investigated using a scramjet test rig. The shear force induced through the ablation load spalled the as-sprayed DC-TBC. The thermal stress mismatch instigated through the difference in coefficient of thermal expansion (CTE) between discrete YSZ and LaMgAl 11 O 19 layers led to the failure of the as-sprayed DC-TBC. The as-sprayed FG-TBC exhibited an improved ablation resistance. The varying thermo-mechanical properties along the ceramic layer thickness in as-sprayed FG-TBC minimise the concentration of thermal stress across the coating and imparts better thermal stability. The improved mechanical interlocking of molten splats during re-solidification of five discrete layers of ceramic composites inhibits the concentration of stress around the weak links. Compared to the textured DC-TBCs, the textured FG-TBCs exhibited minimal level of distortion and better resistance to ablation. The textured surfaces restrict the propagation of crack across the top surface and also provide improved strain tolerance. The graded structure minimises the stress built up and improves the coating resistance compared to textured DC-TBCs. The adhesion strength of all test surfaces was analysed following the standard test procedure. The textured surfaces having higher surface roughness (in terms of surface area) exhibited improved adhesion strength. The groove parameters were observed to have significant influence in improving the ablation resistance and adhesion strength of the coatings.

Influence of Welding Techniques on Heat Affected Zone Softening of Dissimilar Metal Maraging Steel and High Strength Low Alloy Steel Gas Tungsten Arc Weldments

Abstract: The present investigation reports on a study that has been taken up to understand and control the extent of softening in heat affected zone of dissimilar gas tungsten arc (GTA) welds of high strength steels: AISI 4130 steel and 18 % Ni maraging steel which are in hardened condition i.e., maraging steel in solution treated and aged condition and AISI 4130 steel in hardened and tempered condition before welding. The influence of welding technique on the width of soft zone and in-turn on the hardness has been investigated. All the dissimilar joints have been investigated for microstructures, microhardness and tensile properties. It is observed that continuous current GTA welding process results in a wider soft zone, leading to poor mechanical properties, which can be attributed to softer microstructural constituents.

Improvement of strain tolerance of functionally graded TBCs through laser surface micro-texturing

Abstract: Atmospheric plasma-sprayed thermal barrier coating made up of YSZ and LaMgAl11O19/YSZ was plasma-sprayed over nickel-based superalloy. The coated surfaces are textured using a picosecond pulsed laser for different groove geometries. The scanning parameters were optimised to minimise the occurrences of re-cast layer and horizontal cracks. The textured samples were subjected to thermal shock cycles to study their thermal stability. The width-to-depth ratio (W d) and the groove spacing between the adjacent texture were varied to analyse and correlate their geometrical influence in providing thermal stress–strain tolerance. The textured samples exhibit higher lifetime compared to the YSZ and LaMgAl11O19/YSZ as-sprayed surface. The induced thermal stress and minimal strain tolerance in the as-sprayed surfaces result in the traditional interface delamination failure where the failure occurs at the bond coat–ceramic layer interface. The textured grooves having higher W d restrain the propagation of crack across the coating thickness and provide improved strain tolerance. The horizontal cracks initiated at the edge propagates across the textured layer chipped the groove segments within the ceramic bulk layer. The LaMgAl11O19/YSZ-based textured sample having W d of 0.8 and 300 µm groove spacing exhibits higher lifetime of 219 thermal cycles. This implies the significance of groove density in improving the thermal shock resistance of TBCs.

Separation Dynamics of Air-to-Air Missile and Validation with Flight Data

Abstract: Prediction of flight characteristics of a store in the vicinity of an aircraft is vitally important for ensuring the safety of the aircraft and effectiveness of the store to meet the mission objective. Separation dynamics of an agile air-to-air-Missile from a fighter aircraft is numerically simulated using an integrated store separation dynamics suite. Chimera cloud of points along with a grid-free Euler solver is used to obtain aerodynamic force on the missile and the force is integrated using a rigid body dynamics code to obtain the missile position. In the present work, the suite is applied to a flight test case and sensitivity of trajectory variables on launch parameters is studied. Further, the results of the suite are compared with the flight data. The predicted body rates and Euler angles of missile compare well with the flight data.

Numerical Simulation of Hydrogen Air Supersonic Coaxial Jet

Abstract: In the present study, the turbulent structure of coaxial supersonic H2–air jet is explored numerically by solving three dimensional RANS equations along with two equation k–e turbulence model. Grid independence of the solution is demonstrated by estimating the error distribution using Grid Convergence Index. Distributions of flow parameters in different planes are analyzed to explain the mixing and combustion characteristics of high speed coaxial jets. The flow field is seen mostly diffusive in nature and hydrogen diffusion is confined to core region of the jet. Both single step laminar finite rate chemistry and turbulent reacting calculation employing EDM combustion model are performed to find the effect of turbulence-chemistry interaction in the flow field. Laminar reaction predicts higher H2 mol fraction compared to turbulent reaction because of lower reaction rate caused by turbulence chemistry interaction. Profiles of major species and temperature match well with experimental data at different axial locations; although, the computed profiles show a narrower shape in the far field region. These results demonstrate that standard two equation class turbulence model with single step kinetics based turbulence chemistry interaction can describe H2–air reaction adequately in high speed flows.

Experimental investigation on friction stir welding of cryorolled aa2219 aluminum alloy joints

Abstract: In this paper, experimental investigation on cryorolled aluminum AA2219-T87 plate by using friction stir welding (FSW) process is carried out. AA2219-T87 plates with a size of 200×100×22.4 mm were rolled and reduced to 12.2mm thickness (more than 45% of reduction in total thickness of the base material) at cryogenic temperature (operating temperature range −90–−30∘C). The cryorolled (CR) plates have reduced grain size, improved hardness and increased corrosion resistance property compared with the uncryorolled AA2219-T87 plates. FSW joints of cryorolled AA2219-T87 plates were prepared using cylindrical threaded FSW tool pin profile. Mechanical and metallurgical behaviors of friction stir welded joints were analyzed and the effects of the FSW process parameters are discussed in this paper. The variation of microhardness in the FSW joint regions were correlated with the microstructure of FSW joints. Cryorolled plate and FSW joints were tested for corrosion resistance using potentiodynamic polarization test. FSW joints shows better result during the corrosion resistance analysis compared to base AA2219-T87. The X-ray diffraction (XRD) test results showed that fine α-Al grains with eutectic phase (Al2Cu) were present in the weld nugget (WN). The large clusters of strengthening precipitates were reduced in size and merged with the weld nugget portion.

Effect of rocket exhaust of canisterized missile on adjoining launching system

Abstract: Transient numerical simulations are carried out to study missile motion in a vertical launch system and to estimate the effect of missile exhaust in the adjoining launch structure. Three-dimensiona...

Friction Buttering: A New Technique for Dissimilar Welding

Abstract: This work offers a fresh perspective on buttering, a technique often considered for fusion welding of dissimilar metals. For the first time, buttering was attempted in solid state using friction deposition. Using this new “friction buttering” technique, fusion welding of two different dissimilar metal pairs (austenitic stainless steel/borated stainless steel and Al-Cu-Mg/Al-Zn-Mg-Cu) was successfully demonstrated. The results show that friction buttering can simplify a tough dissimilar welding problem into a routine fusion welding task.

Assessment of droplet breakup models in high-speed cross-flow

Abstract: The breakup process in quiescent atmosphere and high-speed cross-flow is numerically simulated. Three-dimensional RANS equations with the K-ε turbulence model are solved using commercial CFD software. Different droplet breakup models, namely, TAB, ETAB, Ritz-Diwakar, and KH-RT models are studied to assess their predictive capability in characterizing spray in high-speed cross-flow. The validation test cases include liquid injection into quiescent atmosphere, and subsonic and supersonic cross-flow. Computed droplet velocity, droplet size, and spray penetration are compared with the experimental/numerical data available in the literature. For diesel injection in quiescent atmosphere, computed spray penetration matches reasonably well with the experimental data. For subsonic cross-flow, although the penetration height is underpredicted, SMD distribution and particle velocity match reasonably well with the experimental data. The ETAB model captures the SMD values at different locations and velocities better with experimental data in comparison to the TAB model. For the supersonic cross-flow case, penetration height and SMD have a good match with the experimental data. The Stokes drag model performs better than the high-Mach and dynamic drag models. Droplet drag law for supersonic flow needs to be revised to have better predictive capability of spray characteristics in high-speed flow.

Corrosion properties of cryorolled aa2219 friction stir welded joints using different tool pin profiles

Abstract: The purpose of this paper is to present the corrosion behavior of the Cryorolled (CR) material and its Friction Stir Welded joints. Due to the thermal cycles of Friction Stir Welding (FSW) process, the corrosion behavior of the material gets affected. Here, the cryorolling process was carried out on AA2219 alloy and CR material was joined by FSW process using four different pin tool profiles such as cylindrical, threaded cylindrical, square and hexagonal pin. The FSW joints were analyzed by corrosion resistance with the help of potentiodynamic polarization test with 3.5% NaCl solution. From the analysis, it is found that CR AA2219 material exhibits good corrosion resistance compared to the base AA2219 material, and also a hexagonal pin profile FSW joint exhibits high corrosion resistance. Among the weld joints created by four different tools, the lowest corrosion resistance was found in the cylindrical pin tool FSW welds. Further, the corroded samples were investigated through metallurgical investigations...

Effect of laser glazing on the thermo-mechanical properties of plasma-sprayed LaTi2Al9O19 thermal barrier coatings

Abstract: Conventional duplex (DL) and functionally graded (FG) LaTi2Al9O19 (LTA) coatings were deposited over C263 nickel alloy by air plasma spray (APS) and compared with subsequent laser glazing processes. The effect of laser glazing on adhesion strength and thermal barrier performance was investigated. The thermal barrier effect was measured using the temperature difference technique involving infrared (IR) rapid heater and the adhesion strength was measured using the scratch tester. The surface morphology and microstructure were analyzed by optical microscopy (OM), Scanning Electron Microscope (SEM) and 3D profilometer. Based on the experimental results, the laser glazing showed a remarkable temperature drop after IR rapid heating. The changes in porosity and grain refinement make more contributions to the temperature drop of the laser-glazed coatings than that of as-sprayed coatings. The temperature drop is about 110°C for laser-glazed LTA FG coating after 100 s of IR flash, while the drop in DL as-sp...

Evaluation of side spillage for a hypersonic air intake using computational fluid dynamic techniques

Abstract: Mass capture ratio of a hypersonic air intake is one of the most important performance parameters. However, no a priori estimate of its value exists for use in initial design exercise of a hypersonic vehicle. In the present work, an air intake of a non-axisymmetric scramjet engine, designed using stream thrust methodology, is studied using computational fluid dynamic techniques. A large amount of air mass flow rate is observed to spill from the sides, which is not accounted for in the initial design phase. In absence of even an approximate estimate of this spillage, computational fluid dynamic studies become the only available tool to evaluate the mass capture ratio. Simulations are also carried out with a side wall at the intake to stop spillage. Although mass capture ratio and static pressure at combustor entry improve, deterioration in other flow parameters such as static temperature, Mach number and total pressure is observed.

Effect of Mach Number on Shock Oscillations in Supersonic Diffusers

Abstract: Unsteady characteristics of shock wave oscillations are one of the most prevalent phenomena occurring in a supersonic diffuser. In such oscillations, significant boundary layer separation leads to a highly unsteady flow field resulting in inlet instability, aircraft buffeting, and aero-structure fatigue. From an engineering point of view, this phenomenon can have a significant impact on performance of supersonic diffusers operating near critical mass flow because of the complex interaction between the boundary layer and many shock waves. This includes a shock-wave/turbulent boundary-layer interaction (SBLI) followed by a subsonic region with an adverse pressure gradient and rapidly thickening boundary layer.

Nonlocal thermodynamic response of a rod

Abstract: Thermally induced behavior of a rod under the influence of a moving heat source is studied in the present work. The thermal behavior is modeled using the non-Fourier heat conduction model and the elastodynamic behavior of the rod is modeled using the nonlocal continuum mechanics. Laplace transformation and Riemann-sum approximation methods are used in the mathematical formulations. Based on the temperature history, the thermally induced nonlocal deformation and nonlocal stress behavior of the rod are studied. The influences of nonlocal scale parameter and speed of the heat source are studied in detail. The results presented in this work are helpful in the design of nanoscale welding, grinding, metal cutting devices, etc., that make use of the thermodynamic behavior within the nanoscale rod.

Numerical Simulation of Missile Jet Deflector

Abstract: A numerical simulation was carried out to estimate the heat flux on a jet deflector caused due to impingement of the rocket exhaust of a canisterized missile. Three-dimensional Navier–Stokes equati...

Damping numerical oscillations in hybrid solvers through detection of Gibbs phenomenon

Abstract: Summary A Gibbs phenomenon detector that is useful in damping numerical oscillations in hybrid solvers for compressible turbulence is proposed and tested. It is designed to function in regions away from discontinuities where commonly used discontinuity sensors are ineffective. Using this Gibbs phenomenon detector in addition to a discontinuity sensor for combining central and shock capturing schemes provides an integrated way of dealing with numerical oscillations generated by shock waves and contact lines that are normal to the flow. When complete suppression of numerical oscillations is not possible, they are sufficiently localized. Canonical tests and large eddy simulations show that inclusion of the proposed detector does not cause additional damping of “well resolved” physical oscillations. This article is protected by copyright. All rights reserved.

Development of ANFIS Model for Flow Forming of Solution Annealed H30 Aluminium Tubes

Abstract: Modeling of the cold flow forming process for manufacturing of tube shaped solution annealed H30 Aluminum alloy has been considered in this present study. Three inputs (feed-speed ratio, roller in-feed and roller axial stagger) and three outputs viz. spring back, ovality and internal diameter have been considered for the present study.. Adaptive network-based fuzzy inference system (ANFIS) in Matlab platform has used for modeling purposes and its performance is compared with regression model. ANFIS has completely outperformed the regression models. Percentage accuracy in predicting all the three responses are found to be very high with ANFIS models. Prediction of ovality against the test data using regression analysis is found to be extremely erroneous. It indicates that additional process parameters are involved in predicting ovality which are not captured during the experimentation.

Numerical Simulation of Non-Equilibrium Plasma Discharge for High Speed Flow Control

Abstract: Numerical simulation of hypersonic flow control using plasma discharge technique is carried out using an in-house developed code CERANS-TCNEQ. The study is aimed at demonstrating a proof of concept futuristic aerodynamic flow control device. The Kashiwa Hypersonic and High Temperature wind tunnel study of plasma discharge over a flat plate had been considered for numerical investigation. The 7-species, 18-reaction thermo-chemical non-equilibrium, two-temperature air-chemistry model due Park is used to model the weakly ionized flow. Plasma discharge is modeled as Joule heating source terms in both the translation-rotational and vibrational energy equations. Comparison of results for plasma discharge at Mach 7 over a flat plate with the reference data reveals that the present study is able to mimic the exact physics of complex flow such as formation of oblique shock wave ahead of the plasma discharge region with a resultant rise in surface pressure and vibrational temperature up to 7000 K demonstrating the use of non-equilibrium plasma discharge for flow control at hypersonic speeds.

Numerical simulation of fairing separation test for hypersonic air breathing vehicle

Abstract: Fairings are provided to cover hypersonic air breathing vehicle to protect it from adverse aerodynamic loading and kinetic heating. Separation dynamics of fairings is an important event in the launch of vehicle. Extensive computational fluid dynamics simulations are carried out for the design of fairings and vehicle and selection of time sequences of various separation events. A ground test of fairing separation is conducted in the sled facility to check the structural integrity and functionality of various separation mechanisms and flight hardware. Simulations have been carried out to study the separation dynamics of fairings at test conditions using grid-free Euler solver to get the aerodynamic loads and the loads are integrated to get the trajectory of fairings. The aerodynamic loads are provided to verify the structural integrity of various components and the trajectory of panels is used in the test planning. The pressure distributions on the vehicle are compared with the test results.

Galvanic interactions of HE15 /MDN138 & HE15 /MDN250 alloys in natural seawater

Abstract: HE15 is a heat treatable high strength alloy with excellent machinability find wide applications in aerospace and defence industries. In view of their excellent mechanical properties, workability, machinability, heat treatment characteristics and good resistance to general and stress corrosion cracking, MDN138 & MDN250 have been widely used in petrochemical, nuclear and aerospace industries. The galvanic corrosion behaviour of the metal combinations HE15 /MDN138 and HE15 /MDN250, with 1:1 area ratio, has been studied in natural seawater using the open well facility of CECRI’s Offshore Platform at Tuticorin for a year. The open circuit potentials of MDN138, MDN250 and HE15 of the individual metal, the galvanic potential and galvanic current of the couples HE15 /MDN138 and HE15 /MDN250 were periodically monitored throughout the study period. The calcareous deposits on MDN138 and MDN250 in galvanic contact with HE15 were analyzed using XRD. The electrochemical behaviors of MDN138, MDN250 and HE15 in seawater have been studied using an electrochemical work station. The surface characteristics of MDN138 and MDN250 in galvanic contact with HE15 have been examined with scanning electron microscope. The results of the study reveal that HE15 offered required amount of protection to MDN138 & MDN250.

A novel pressure sensor using eddy current principle for Harsh environment

Abstract: In Aerospace applications, transient pressure measurement in harsh environment using strain gauge type of pressure sensor, suffers due to the limitations of strain gauges and contact transduction method. In this paper, a novel pressure sensor using eddy current principle has been proposed with complete design to overcome the challenges faced by the other type of pressure sensors in harsh environment. Unlike magnet based transduction, the designed pressure sensor does not require recalibration after every use as the target will not loose its properties for short duration of high temperature exposure. The performance evaluation of the designed sensor supported by simulated test results is presented for analysis and improvement. Further scope of work towards improvement of accuracy, bandwidth and miniaturization has been concluded to aid sensor design in future.

Temperature monitoring system with remote calibration capability

Abstract: This paper proposes a novel implementation of self-calibration in a temperature monitoring system that employs thermocouple as a temperature sensor for propellant and highly inflammable storage facilities where human frequent intervention for calibration of temperature sensors is not affordable. In the proposed design, we have implemented a comparison methodology for calibration of these thermocouples. To realize this, a Peltier heater has been used as a heat source whose temperature is controlled by a micro-controller through MOSFET. A pair of thermocouples with different accuracies is mounted on each Peltier heater and the temperature difference between them is measured subsequently in steps. Flexibility to access the system both in wireless mode (using ZigBee module) or wired mode (using ETHERNET module) has been provided. A graphical user interface has been developed in LabVIEW to monitor the temperature, calibrate the thermocouples and also to simultaneously store the data. A detailed description of the system and relevant test results have been presented in the paper.

Plume Interaction and Base Flow Analysis of a Twin Engine Flight Vehicle

Abstract: 3D RANS simulations are performed to study the multi jet interactions of a twin engine gimbal configuration of an aerospace vehicle at different time instants. Simulations captured all the essential features of the flow field and interaction between the neighboring jets did not occur because of low altitudes and moderate under-expansion of the jets considered in the simulations. For higher gimbal angle, two jets were the closest but still did not interact. Detail exploration of the downstream flow field revealed that the distinct features of the jets are retained at the farthest downstream locations; although the pressure field reached the uniformity. Average base pressure ratios for the three different time instances are 0.91, 0.547 and 0.522 and maximum base temperature is of the order 800 K.

Numerical Simulations of Canted Nozzle and Scarfed Nozzle Flow Fields

Abstract: Computational fluid dynamics (CFD) techniques are used for the analysis of issues concerning non-conventional (canted and scarfed) nozzle flow fields. Numerical simulations are carried out for the quality of flow in terms of axisymmetric nature at the inlet of canted nozzles of a rocket motor. Two different nozzle geometries are examined. The analysis of these simulation results shows that the flow field at the entry of the nozzles is non axisymmetric at the start of the motor. With time this asymmetry diminishes, also the flow becomes symmetric before the nozzle throat, indicating no misalignment of thrust vector with the nozzle axis. The qualitative flow fields at the inlet of the nozzles are used in selecting the geometry with lesser flow asymmetry. Further CFD methodology is used to analyse flow field of a scarfed nozzle for the evaluation of thrust developed and its direction. This work demonstrates the capability of the CFD based methods for the nozzle analysis problems which were earlier solved only approximately by making simplifying assumptions and semi empirical methods.

Mitigation of shock-induced flow separation using magnetohydrodynamic flow control

Abstract: A numerical investigation is carried out to demonstrate a proof of concept, magnetohydrodynamics-based active flow control, for mitigation of laminar flow separation over a flat plate due to shock wave–boundary layer interaction. The CERANS-MHD code has been used to solve the governing resistive magnetohydrodynamic equations discretized in finite-volume framework. The AUSM-PW+ flux function is used in modelling the advection terms and central differencing is used in modelling the resistive terms. Powell’s source term method is used for divergence cleaning of the magnetic field. The Hartmann number is varied from 0 to 12,000 to effectuate mitigation of flow separation, with the magnetic field applied at the wall and oriented transverse to the flat plate flow direction. Due to the Hartmann effect, flow separation is observed to be suppressed with increase in Hartmann number beyond 6000. However, the overall magnitude of skin friction distribution increases drastically, resulting in large increase in skin friction drag as compared with the non-magnetic case, and is a cause of concern.