Defence Science Journal
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A Unified Mechanics Theory based Damage Model for Creep in Nickel based Superalloys
Full text linkUnified Mechanics Theory’s (UMT) entropy-based damage parameter, also known as the “Thermodynamic State Index” has been proven to be consistent and useful in predicting the fatigue life of different metal alloys. In recent times, studies have also demonstrated its applicability towards creep damage in nickel-based superalloys under a limited set of conditions. However, the usefulness of the “Thermodynamic State Index” in estimating damage at different temperatures, and creep loads for different metal alloys has not been evaluated yet. In this paper, creep in INCONEL 600 alloy is modeled using Norton’s creep law modified with entropy-based damage (Thermodynamic State Index). The model is calibrated to predict both damage and creep strains for any given input of stress, temperature, and time. The available database on INCONEL 600 is used in parts to both calibrate and validate the prescribed model. The damage evolution for different cases is compared and imminent conclusions are drawn
A A New Approach in Realisation of DGS Microstrip Patch Antennas With Fractal Geometry
No full textA new approach in realization of Defected Ground Structure Microstrip Patch antennas with Fractal Slots cutin the ground plane has been presented. The presented approach resulted in miniaturization of radiating patches and avoidance of multiple resonances which are prime considerations in antennas for Wi-Fi applications. A rectangular Microstrip patch is taken as a basic radiating patch. In the ground plane, square and circular slots following Sierpinski Carpet Fractal Geometry are cut resulting in Defected Ground Structure (DGS) Microstrip Patch antenna. The antenna is designed to operate at 2.4 GHz and the performance characteristics have been simulated using HFSS software. The proto-type DGS Microstrip patch antenna with square fractal slots is fabricated and tested. The measured results are in good agreement with the simulation studies. The technique has also resulted in size reduction of radiating patch compared to the standard microstrip patch antenna operating at the same frequency
Design of a Low Profile Archimedean Spiral Antenna using Compact Defected Ground Structure as a Reflector
Full text linkIn this paper, design and realisation of a low profile Archimedean spiral antenna is presented. The low profile Archimedean spiral antenna is printed on a substrate and backed by a reflector consisting of DGS. The DGS unit cell consists of a parallel combination of meander line inductors and inter-digital capacitors. This, DGS is one of the forms of electromagnetic band gap (EBG) structures providing electromagnetic band gap characteristics. It is used as a reflector with spiral antenna to achieve unidirectional radiation properties and a low profile of antenna. A modified version of uniplanar EBG cell is used as a DGS cell. This cell is used for configuration of the DGS ground plane. This ground plane is evaluated for its electrical characteristics and used as a reflector for the spiral antenna. Archimedean Spiral antenna is designed and simulated in the frequency band of 1-6GHz with DGS as a reflector. The antenna characteristics are studied for physical parameters of the antenna. These parameters are optimized for better electrical characteristics. The performance of the proposed antenna is also compared with conventional metallic (PEC) reflectors. Simulated results of an antenna are validated by measurement. Antenna height reduction of 60% is achieved compared to conventional cavity-backed spiral antennas
Design Validation and Reliability Assurance of Electronic Systems Using the Next Generation RGT Models
Full text linkArrhenius Accelerated Growth Model (AAGT) is the next generation accelerated testing models used for design validation and reliability assurance of electronics systems. These models are used in design and manufacturing phases towards reliability enhancement of the system respectively. AAGT Models uses Highly Accelerated Stresses for screening of the components towards uncovering Compared to traditional qualification test methods, design flaws, latent defects, component selection problems, and manufacturing flaws can be detected fast. The procedure includes thermal dwells and quick temperature changes while subjecting the test unit to increasing degrees of stress. Dynamic stresses (Pseudo-Random Vibration covering all 6DOF systems) and a combination of thermal and dynamic PSD stresses towards quickly precipitating inherent/hidden defects quickly. These Accelerated models used to qualify modern active array radar modules like Transmit Receive Modules (TRMs) which will be in large numbers and It will be difficult and time-consuming to filter these modules individually using the traditional way. To increase the quality and dependability of electronic devices, much accelerated life tests have been extensively adopted. However, extremely accelerated life tests may only be used as a qualitative approach to assess a product's dependability; they cannot be used to quantify a product's reliability, such as MTBF/MTTF. Consequently, in order to efficiently assess the level of product reliability while improving product reliability in a timely manner. HALT/HASS uses Arrhenius Accelerated Growth Model that is an effective technique used for screening of the module with in short period. This paper discuss in detail with a case study on active array modules deliberating about the test methodology, challenges faced during Using Arrhenius accelerated test models, rapid testing and assessment of these Four channel TRMs used for airborne Fire Control Radar for combat operations
Analysis of Pilot Distance Estimation in Different Lighting and Visibility Conditions
Full text linkSeveral studies on distance and size estimation have focused on normal and night vision goggles (NVGs), but none of them have been performed during the twilight period. Hence, in this study, distance was estimated for the first time during nautical twilight. According to the findings, the accuracy of distance estimation reduces as visibility decreases and is restricted. When compared with Day Limited Helmet Mounted Display Vision (M = 5.27, SD = .59), Twilight Normal Vision (M = 5.33, SD = .69) and Twilight Helmet Mounted Display Vision (M = 5.20, SD = .61), NVG (M = 4.79, SD = .57) appears to have a lower error rate. In this study, distance was estimated considering objects determined during the helicopter flight by the pilots in different visibility conditions, which are significant in the field of aviation. This work is unique owing to its coverage of helicopter pilots and the estimation during the twilight period. In view of our findings, it may be reasonable to postpone the planned helicopter flights during poor visibility conditions
Analysis of Pleated Discrete Pore Non Woven Layer Type Filter Element for Naval Applications
Full text link In naval applications generally, the pleated discrete pore non-woven layer filter element is used. Filters used for such applications require maximized filtration rate, lower pressure drop, higher permeability, effective pore size distribution and good filtration efficiency. In other most common wire mesh filter element types, the geometric parameters are well defined and can easily be modelled. In the case of non-woven layer filter elements the pores are arranged in a randomly distributed manner and the modelling becomes difficult. In this present study a new approach was contemplated for modelling the same. The fluid flow through the filter element is by percolation phenomenon. Using Darcy’s law approach, the pressure drop across the filter element for different flow rates, were found analytically by considering the flow resistance in axial, radial and circumferential directions. The theoretical prediction made by CFD analysis is correlated with actual model behaviour and a good degree of correlation is obtained which shows the efficacy of this method for wider use in similar application.
 
Simulation of Explosion Crater of Earth Penetrating Nuclear Bomb Based on Equivalency to TNT Mass
Full text linkThe structure size of the crater formed by the earth-penetrating nuclear bomb explosion is one of the important parameters for evaluating the earth-penetrating nuclear bomb damage power. Obtaining the structure size of the crater formed by the earth-penetrating nuclear bomb explosion with different yields is great significance for the evaluation and design of the nuclear bomb damage power. In this study, considering the contradictory relationship between the structure size of the earth-penetrating nuclear bomb and the structure size of the equivalent TNT mass, we propose to use the equivalent energy mapping method to realize the finite element numerical simulation of the earth-penetrating nuclear bomb exploding into craters analyzed and compared the simulation results with the structure size of the crater formed by the ESS nuclear bomb explosion in the United States. The analysis results show that the error between the simulated crater radius and the real crater radius is 3.26%, and the error between the simulated crater depth and the real crater depth is 28.57 %. It meets the calculation accuracy error range of crater formation from nuclear explosion to chemical explosion. Therefore, this method provides an effective numerical simulation method and a means of obtaining the structural size data of the explosion crater for the earth-penetrating nuclear bomb cratering
Experimental study on dynamic mechanical properties of projectile 155mm ERFB BT material
Full text linkArtillery projectile 155mm high explosive (HE) extended range full bore boat tail (ERFB BT) and its components experience a high pressure loading of the propellant during gun launch. Mechanical properties of an engineering material are measured using quasi-static tensile test at room temperature. The materials of the projectile and its components are expected to survive time dependent propellant pressure loading inside the gun, which lasts for few microseconds. To investigate dynamic mechanical properties of the projectile and its components at medium strain rates and elevated temperature, the experimental analysis is undertaken. This research paper aims to examine the effect of medium strain rates and elevated temperatures on flow properties of the materials used in the projectile. The uniaxial tensile tests at the medium strain rates between 0.01 s-1 to 1s-1 and at elevated temperatures ranging between 150°C to 500°C are performed separately. The Considѐre criterion was applied to evaluate strain hardening exponent of the materials. Values of strain hardening exponents of shell body and boat tail materials are less than that of driving band material. Strain rate sensitivity of the materials is observed to be very low, thus indicating a good resistance to plastic deformation. The yield strength and true yield strength of the materials fall with increase in temperature.
 
Development of Tribological Coatings for Aerospace and Missile Applications
Full text linkTribological coatings play a key role in enhancing the performance and service life of engineering systems and components. Over the years, DMRL has worked extensively in studying various aspects of tribological coatings used in aerospace and missile propulsion systems where harsh and hostile environments prevail. The coatings have been deposited mostly by thermal spray processes for these applications. The studies have been done to understand the relationship between microstructure, mechanical properties and tribological behaviour of coatings. In this work, a cermet coating based on carbide to resist wear and an abradable coating based on cobalt alloy to control clearance between the blade tip and shroud for gas turbine aeroengine application and a low friction coating developed for a missile application will be discussed.