Showing papers by "Defence Research and Development Laboratory published in 2019"

Dissimilar Welding of Maraging Steel (250) and 13-8 Mo Stainless Steel by GTCAW, LBW and EBW Processes

Abstract: The frequently used aerospace materials, i.e., ultra-high-strength maraging steel (250) and corrosion-resistant 13-8 Mo stainless steel in the solution-annealed and cold-worked condition, have been joined by three fusion welding processes, namely interpulse TIG welding, and high energy density fusion processes like electron beam welding (EBW) and laser beam welding (LBW). The interpulse TIG welding process was carried out by using W2 grade maraging steel filler wire. The dissimilar joints were welded by EBW and LBW processes without any filler wire. All the dissimilar welded joints were characterized by microstructural observations and validated by mechanical properties in the as-welded as well as precipitation-hardened conditions after welding. The weld microstructures and microhardness profiles were correlated to the tensile strength of weld. Electron beam welded joint with precipitation hardening after welding, i.e., soaking at 510 °C and subsequent air cooling, demonstrated the superior mechanical properties among all the welds.

Compressibility, Damage and Age Hardening effects of Solid Propellants using Finite Strain Constitutive Model

Abstract: In this paper, the finite strain viscoelastic constitutive model for particulate composite solid propellants is proposed considering strain rate, large deformation/large strain, thermorheological behavior, stress softening due to microstructural damage, compressibility, and chemical age hardening. The compressible Mooney–Rivlin hyperelastic strain energy density function is used along with the standard model of viscoelasticity. To model the compressibility, the dilatational strain energy is taken as the hyperbolic function of the determinant of deformation gradient. The stress-softening phenomenon during cyclic loading (Mullin's effect) due to microstructural damage is described by an exponential function of the current magnitude of intensity of strain and its previous maximum value. The variation of material properties with time are studied using the isothermal accelerated aging technique through simulation and experimental investigation. The comparison of predictions based on the proposed model with the uniaxial experimental data demonstrates that the proposed model successfully captures the observed behavior of the solid propellants.

An intelligent gain-based ant colony optimisation method for path planning of unmanned ground vehicles

Abstract: In many of the military applications, path planning is one of the crucial decision-making strategies in an unmanned autonomous system. Many intelligent approaches to pathfinding and generation have been derived in the past decade. Energy reduction (cost and time) during pathfinding is a herculean task. Optimal path planning not only means the shortest path but also finding one in the minimised cost and time. In this paper, an intelligent gain based ant colony optimisation and gain based green-ant (GG-Ant) have been proposed with an efficient path and least computation time than the recent state-of-the-art intelligent techniques. Simulation has been done under different conditions and results outperform the existing ant colony optimisation (ACO) and green-ant techniques with respect to the computation time and path length.

A review: advancements in fluoro-based polymers for aggrandizing anti-galling and wear resistant characteristics

Abstract: Galling is the surface phenomenon which involves adhesion of local contact points and creation of protrusions on the juxtaposition of surfaces owing to high friction, inappropriate tribological loading, starved lubrication and high contact pressure (~ 1000 kPa). All these factors result in severe plastic deformation varying from 8000 to 10,000 µe (e-strain) and diffusion of materials into one another, which consequently results in fatigue wear, surface roughness, tribocorrosion and seizing up of critical parts. The aim of the review is to analyze and summarizes the issue of galling, concurrently it also deals with the novel and economical mitigation method i.e. use of fluorine based coatings e.g. PTFE, owing to their lowest friction coefficient from 0.02 to 0.2 among other solids, high stiffness, high thermal stability and non-adherent characteristics that augments the mechanical and tribological properties and concurrently protect against hostile environments that eventually upsurges the life of components.

Effects of Angle of Attack and Bluntness on Heating Rate Distribution of Blunt Models at Hypersonic Speeds

Abstract: The effects of nose radius on stagnation and surface heat transfer rate along the surface are addressed in this research paper. Experiments are carried out in hypersonic shock tunnel, at hypersonic Mach number of 6.56 for 11.38° apex angle blunt cone with nose radius of 0.2R, base radius of R. Similarly, experiments are carried out at Mach 7.32 for 13.87° apex angle blunt cone models with nose radius of 0.18R′, base radius of R′. Test is performed at stagnation enthalpy of 1.4 and 2 MJ/kg with effective test time of 3.5 ms. Convective heat transfer measurements have been carried out on the test model at two different angles of attack, namely 0° and 5° with angle of rotation of 0°, 90°,180° with platinum thin film sensors. ANSYS-Fluent used to simulate the flow over the blunt models at different Mach numbers. The measured shock standoff distance from Schlieren visualization images compared with theory and computational fluid dynamic study for both configurations. The measured stagnation heating value is compared with theoretical value estimated using Fay-Riddell expression and numerical simulation. The measured heat transfer rate is higher for configuration 1 than configuration 2. The increases in heat transfer rate is due higher density ratio across the shock wave and the reduced shock layer thickness. The measured shock layer thickness is 2.06 mm for Mach 6.56 and 3.45 mm for Mach 7.32. The heat transfer rate is higher for Mach 6.56 as compared to Mach 7.32.

Evaluation of structural integrity of tactical missile ceramic radomes under combined thermal and structural loads

Abstract: Radome is a thermo-structural member used in tactical missiles and houses the avionic systems like seeker. It is subjected to severe thermal as well as structural loads during the flight. The material of the radome is chosen such that it is transparent electromagnetic radiation. The ceramic radome is attached to the metallic bulkhead with high temperature glue. In the present manuscript, the experimental evaluation methodology implemented for evaluation of the structural integrity of the ceramic radome under combined thermal and structural loads is presented. Initially axial load, to simulate the resultant drag force and a distributed lateral load, to simulate the bending moment, are applied via a pre-casted contoured Teflon mock sections, up to proof load and then time varying temperature is applied. The time-varying temperature profile is applied via a closed loop control based on PID and the heating environment is created using short wave infra-red radiation. Exhaustive instrumentation is used in the experiments. Detailed results are also presented in the manuscript up to the structural failure.

Convective heat-transfer rate and surface pressure distribution over a cone model at hypersonic speeds:

Abstract: In this article, experiments are carried out in a hypersonic shock tunnel with helium as driver gas and air as the test gas to obtain the convective heating rate and surface pressure distribution o...

Dynamic pressure based mid-course guidance scheme for hypersonic boost-glide vehicle:

Abstract: In this study, a guidance scheme for an aerodynamically controlled hypersonic boost-glide class of flight vehicle is proposed. In this work, optimum glide dynamic pressure corresponding to maximum ...

Censored Spectrum Sharing Strategy for MIMO Systems in Cognitive Radio Networks

Abstract: Multi-antenna technologies have been widely used in modern wireless communication systems to achieve diversity gain, spatial multiplexing gain, and better interference suppression. Beamforming has been considered as a potential candidate for throughput maximization in MIMO cognitive radio networks. However, the efficient implementation of beamforming demands for accurate knowledge of channel estimate. Conventional spectrum sharing strategies treat the detection and estimation problems in uncoupled manner, which may not result in the overall optimum performance. In this paper, we propose a censored spectrum sharing strategy which considers both the detection and estimation performances simultaneously and is capable of improving the throughput of MIMO cognitive radio network. We derive analytical expressions for the critical parameters and provide simulation results to validate our derivations.

Physical layer security using an adaptive modulation scheme for improved confidentiality

Abstract: Establishing secured communication among the intended users of wireless networks is a major concern. Especially, providing confidentiality is a critical requirement in a wireless communication system which is more susceptible to eavesdroppers. Prevailing cryptographic methods were proven to meet the security needs to some extent. Sophisticated encryption techniques cannot be always deployed in wireless devices, where the resources are limited. However, physical layer security is recently emerging into a promising paradigm to aid security in wireless networks by exploiting the dynamics of wireless channel. In this study, a physical layer security technique was proposed to enhance confidentiality which selects the modulation type adaptively, based on both channel signal-to-noise ratio and phase between transmitter and receiver. The performance of the proposed technique is evaluated for two types of eavesdroppers such as random and intelligent attackers through simulations. The proposed method improves confidentiality and throughput while maintaining the targeted symbol error rate than the existing algorithms.

Condition Monitoring of Abrasive Waterjet Milling Using Acoustic Emission and Cutting Force Signals

Abstract: Abrasive waterjet machining (AWJM) is widely used in the industries with the distinct advantages of no thermal distortion, high flexibility, small cutting forces, etc. In this work, the influence of abrasive waterjet milling (AWJ milling) process parameters such as waterjet pressure (P), traverse rate (TR), abrasive flow rate (AFR) and standoff distance (SOD) on the depth of cut (DOC), material removal rate (MRR) and surface roughness (Ra) were studied. An attempt has also been carried out to monitor the AWJ milling using two sensors namely, acoustic emission (AE) and cutting force dynamometer. The acquired AE sensor signal is analysed in the time- and frequency domains, whereas the cutting force signal is analysed in the time domain. The result indicated that AE and cutting force signals are influenced by the changes in the input process parameters conditions.

Effect of Helical Winding Angle on External Pressure based Buckling of Partially Filled Thin Composite Cylindrical Shells

Abstract: Effect of helical winding angle on buckling load of thin composite tubes is investigated in this work. Experiments are conducted on both empty and partially filled S2 glass tubes to estimate contribution of strength to the tubes by the filler material. Chosen filler material mechanically simulates behavior of typical solid propellant used in aerospace application. FE analysis with non-linear effect correlates well with the experimental data. Three series of experiments are conducted to quantify effect of helical winding angle and increase in volumetric loading fraction(VLF). Results confirm appreciable improvement in strength of filled tubes for higher VLF. For the chosen pattern of winding, lower winding angle provides more strength to the tubes against external pressure buckling.

Fixed Final Time Field of View and Impact Angle Constrained Guidance

Abstract: A three-dimensional strap-down seeker based field of view and impact angle constrained guidance law for the interceptor is proposed in this paper. When the interceptor is guided based on strap-down seeker measurements, the field of view limit throughout the flight trajectory is one of the major concerns to guarantee tracking of the target. Also, while approaching a target, to enhance the capability of warhead, the interceptor needs to satisfy the desired impact angles. To meet these requirements, the proposed guidance is designed using the computationally efficient, suboptimal state constrained generalised model predictive static programming technique in a specified final time framework. This law also ensures near zero miss-distance with minimal control (lateral acceleration) effort and fixed interception time. The robustness of the proposed guidance design is studied in presence of uncertainty in aerodynamic parameter.

A Low-Cost, High-Performance Implementation of RSA Algorithm Using GPGPU

Abstract: Information security has been of great use in various civilian and defence domains. However, the arduous procedures involved in securely establishing a common key lead to asymmetric-key encryption. The high computational needs of asymmetric-key encryption process made them impractical to be used for real-world applications. The proliferation of low-cost, high-performance computing through GPGPUs made many applications with high-performance requirements feasible to implement and use in real-world applications. A successful attempt has been made to implement RSA algorithm using GPGPU and the results are presented in this paper.

Heat transfer rate and surface pressure measurements in short duration hypersonic flow

Abstract: Experiments were carried out with air as the test gas to obtain the surface convective heating rate and surface pressure distribution on blunt and sharp cone models flying at hypersonic speeds. Tests were performed in a hypersonic shock tunnel at two different angles of attack: and with angles of rotation , and . The experiments were conducted at a stagnation enthalpy of 1.4MJ/kg, flow Mach number of 6.56 and free stream Reynolds number based on the model length of . The effective test time of the shock tunnel is 3ms. The results obtained for cone model with a bluntness ratio of 0.2 were compared with sharp cone models for . The measured stagnation heat transfer value matched well with the theoretical value predicted by the Fay and Riddell correlation and with the CFD results.

Design of an Attachment Scheme of a Vehicle to a Typical Fighter Aircraft

Abstract: Design of an attachment scheme of a flight vehicle to a fighter aircraft is a critical task. Here, flight vehicle is a cylindrical body and it is attached to fighter aircraft with the help of a component called launch lug. Loads experienced by the flight vehicle in captive condition have been estimated by using aircraft parameters obtained during previous missions of similar kind of vehicles. This paper provides state of the art design consideration of the attachment scheme (launch lug and shell assembly) of the flight vehicle to the fighter aircraft. The structural integrity of the flight vehicle and its attachments scheme to the fighter aircraft has been verified at various aircraft manoeuvring conditions in its flight envelope through analysis. Design is verified using laboratory testing and in field trials. Finally this flight vehicle with the attachment scheme was used in flight trials.

Geometric imperfection modelling for buckling of filled thin composite cylinders

Abstract: Initial geometric imperfection plays a vital role in determining realistic buckling load of any structure. Thin cylindrical shells are prone to dimensional imperfection depending on the man...

Development of Welding Fixture for Rocket Motor Casing Assembly

Abstract: Rocket motor casing assembly is the critical and most significant assembly for an aerospace vehicle. Rocket Casing assembly is welded construction, consists of flow formed shell, front flange, aft flange, and external components like launch shoe, wing brackets, and wire tunnel lugs. The assembly of these components is carried out in two stages by tungsten insert gas welding. First stage is assembly of flanges to the shell and second stage is the assembly of external components to the flange subassembly. Four welding fixtures are developed for realization of rocket motor casing assembly. First fixture is designed for stage one (flange subassembly) to maintain correct relationship and alignment between flanges and shell. Remaining fixtures to align, locate the launch shoe, wing brackets, and wire tunnel lugs in a given orientation and position with respect to motor casing. Designed, developed, and utilized welding fixtures for realization of rocket motor casing.

Challenges in Machining of Silica–Silica Cone for Aerospace Application

Abstract: Silica–silica composites are generally used in high-end aerospace applications. They are highly temperature resistant, have low thermal conductivity and low density, and are abrasive in nature. Additionally, due to the soft and brittle nature of the material, it poses challenges during the machining and clamping of the workpiece for achieving the required shape and size. In realizing quality hardware, it becomes very critical to suitably plan the machining strategy. A manufacturing methodology is established to carry out machining of silica-based composite with primary focus on the development of special turning fixtures as a shop setup. This paper discusses the criticalities involved in the machining of the silica material using suitably developed fixtures.

Galvanic Interactions of 15CDV6/MDN138 & 15CDV6/MDN250 Alloys in Natural Seawater

Abstract: The galvanic corrosion behavior of the metal combinations 15CDV6/MDN138 and 15CDV6/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 15CDV6 of the individual metal, the galvanic potential and galvanic current of the couples 15CDV6/MDN138 and 15CDV6/MDN250, were periodically monitored throughout the study period. The calcareous deposits on MDN138 and MDN250 in galvanic contact with 15CDV6 were analyzed using XRD. The electrochemical behavior of MDN138, MDN250, and 15CDV6 in seawater was studied using an electrochemical work station. The surface characteristics of MDN138 and MDN250 in galvanic contact with 15CDV6 have been examined with a scanning electron microscope. The results of the study reveal that the galvanic protection offered by 15CDV6 to MDN250 and MDN138 in natural seawater amounts to 93% and 98%, respectively, implying that the galvanic protection offered by 15CDV6 is continuous and effective, which has been further evinced from the adherent nature of the calcareous deposit film comprising compounds such as CaCO3 (calcite, aragonite, and vaterite), MgCO3 (magnesite), Mg(OH)2 (brucite), and MgO (brucite).