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 | Analytical Evaluation of Fibre Reinforced Plastic Corrugated Sheet
Author : Pathak, R.C. ;Gautam, C.K.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 105-113
Subject : 620.1 Material Science and Technology
Keywords : Materials science ;Fibre reinforced composites
Abstract : Fibre-reinforced composites play lead role as advanced materials in modern day structures. This paper reports fabrication and testing of fibre-reinforced corrugated sheet employing 4-point bend loading. An in-depth analysis has been carried out using ANSYS, a finite element method package. The theoretical results obtained are compared with the experimental values. The values of both inputs showed similar results conforming at a particular boundary condition. However, more similar experiments on such fibre-reinforced plastic corrugated sheets have been suggested for better comparison. |
| | Differential Ballistic response of Aramid Glass Fibre Laminates to Soft and Hard Shots
Author : Saraf, M.N. ;Rao, S.S.;Balakrishna Bhat, T.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 115-118
Subject : 623.45 Ammunition;623.4 Armaments and Ballistics
Keywords : Ball ammunition ;Glass fibre phenolic composites;Armour piercing bullets
Abstract : Ballistic performance of all-glass, all-aramid and aramid-glass fibre-reinforced phenolic resin composite laminates has been evaluated against 0.30 in. calibre soft ball and hard armour piercing (AP) bullets. It is observed that mass effectiveness of glass fibre phenolic composites against impacts by AP bullets can be improved by aramid fibre reinforcement in the back of laminate. The performance of aramid phenolic composites against ball ammunition can be improved by hybridisation with glass fibre reinforcement at the front. |
| | Burn Rate Modelling of Solid Rocket Propellants
Author : Chopra, A.K. ;Kumar, Ramesh;Chaudhary, K.L.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 119-123
Subject : 662.3 Propellants;629.76 Rockets and Missiles
Keywords : Buckingham theorem ;Solid rocket propellant
Abstract : A generalised model of burning of a solid rocket propellant based on kinetics of propellant has been developed. A complete set of variables has been formed after examining the existing models. Buckingham theorem provides the functional form of the model, such that the existing models are the subcases of this generalised model. This proposed model has been validated by an experimental data. |
| | Studies on Physico Mechanical and Explosive Characteristics of RDX HMX Based Castable Plastic Bonded Explosives
Author : Phadke, (Ms) V.K. ;Prakash, Vinay;Tadas, V.V.;Sinha, R.K.;Gharia, J.S.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 125-130
Subject : 620.261 Explosives
Keywords : Composite material;Plastic bonded explosive;Conventional cast explosives;Plasticizer ratios;Polybutadiene based castable
Abstract : Conventional cast explosives (RDX/TNT) have major drawbacks of poor mechanical properties, shrinkages and higher sensitivity. These properties can be improved by applying plastic binder systems. The plastic-bonded explosive (PBX) is a composite material in which solid explosive particles are dispersed in a polymer matrix. The present paper describes the development of a nitramine/hydroxy-terminated polybutadiene (HTPB)-based castable PBX. The PBXs were processed as per standard procedures. Bimodal/trimodal particle size system was selected to reach a solid loading of 88 wt per cent. High solid loading was made possible through proper combination of coarse/fine ratio of solid ingredients, which was based on a number of tap density experiments. Processability of the binder system was studied by using various wetting agents as well as by selecting binder/plasticizer ratios. Mechanical properties of the PBXs were enhanced by different crosslinking agents. The explosive properties of PBXs including detonation velocity, processability and sensitivity to different types of stimuli, were studied. The results show that PBXs can be manufactured with detonation properties better than those of composition B/octol with the added advantages of superior thermal and sensitivity characteristics. |
| | Recent Trends in Smart Technology
Author : Jain, V.K.;Jalwania, C.R.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 21-29
Subject : 621.315.592 Semiconductors
Keywords : Microflow meter ;Microelectromechanical systems;Miniaturised system;Microsensor
Abstract : Integration of a microsensor, microactuator and intelligent control at one place can provide a miniaturised system. Such devices go under different names, such as smart structures, smart sensors or microelectromechanical systems (MEMSs), etc. The functioning of these systems is analogous to biological pattern of functioning. The sensors gather information, analyse through electronic microprocessors and then actuate accordingly. These devices have applications in medicine, aerospace, automotive and defence systems. Though some systems have been developed, most of them are in the development stage or conceptual stage. This paper presents a review of smart technology and also describes a microflow meter integrated with an optical sensor developed in this Laboratory . |
| | Structure of II VI Lattice Mismatched Epilayers used for Blue Green Lasers for Underwater Communication
Author : Willander, M. ;Jain, Uma;Jain, S.C.;Maes, H.E.;Pinardi, K.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 31-43
Subject : 621.315.592 Semiconductors
Keywords : Residual strain ;Equilibrium theory;Semiconductor epilayers;Uncapped lattice;Critical thickness
Abstract : Critical thickness (h/sub c/) is calculated for capped and uncapped lattice mismatched II-VI semiconductor epilayers. Both the old equilibrium theory and the improved theory have been used. The calculated values are compared with the experimental data on epilayers of several II-VI semiconductors and alloys. The observed values of h/sub c/ are larger than the calculated values. However the discrepancy is much smaller than that found in InGaAs/GaAs and GeSi/Si layers. Moreover as compared to InGaAs/GaAs and GeSi/Si layers, the experimental data show a much smaller scatter and can be fitted with one curve. Strain relaxation in layers with thickness h > h/sub c/ is also calculated. Strain relaxation in ZnSe layers grown on (100) GaAs shows good agreement with the equilibrium theory. In other cases the observed relaxation is sluggish, the residual strain is larger than its calculated value. Thick highly mismatched layers behave differently. The residual strain agrees with theory and dislocations are distributed periodically. A model to interpret these observations is suggested. Implications of this study on the stability of II-VI strained layers are discussed. |
| | Semiconductor Switching devices: Future Trends
Author : Ahmad, S.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 45-59
Subject : 621.315.592 Semiconductors
Keywords : Atom relay transistor ;Simulations;Potential barrier;Resonant tunneling;Quantum dot;Quantum wire
Abstract : A variety of semiconductor devices and circuits have been successfully developed using conduction properties of electrons and holes in a number of elemental and compound semiconductors. Carriers confinement in a potential well, formed out of a thin layer of lower band gap material sandwitched between two layers of a higher band gap material, has been extended from one to two and three dimensions. Resultant of two-dimensional carrier sheet, quantum wire and quantum dot having discrete energy levels arising out of quantisation are being presently explored for possible device applications. A number of devices have been fabricated using resonant tunneling across a thin potential barrier. This has opened up several newer possibilities of using such structures for various electronic and optoelectronic devices and circuits applications as tunneling is relatively faster than conduction process. While looking into the interband tunneling between two quantum dots, possibility of a single electron switching has also been examined carefully. The idea of a single electron switching is conceptually being extended from quantum dots to molecules and atoms ultimately. Simulations based on transmission of electrons through a chain of molecules and atoms have shown that tens of THz speed and functional device density 1012 devices/mm2 are possible with such schemes. Devices based on atom relay transistor (ART) will be ultimate in its performance of switching speed. A brief on present-day situation followed by future proposals of fast switching devices for information electronics has been discussed. |
| | Micromachining for Microelectromechanical Systems
Author : Bhat, K.N.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 5-19
Subject : 621.315.592 Semiconductors
Keywords : Micromoulding (LIGA) process ;Microelectromechanical systems;Microengineering;Micromachining
Abstract : The various micromachining processes required for microengineering and for the successful realisation of microeletromechanical systems on Si are presented. The techniques presented include bulk and surface micromachining, Si fusion bonding, and the lithography, electroforming and micromoulding (LIGA) process. The paper also includes discussion on the markets, applications and future trends for microenginerated products. |
| | Luminescence from Porous Silicon
Author : Jain, V.K. ;Gupta, (Mrs) A.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 61-68
Subject : 621.315.592 Semiconductors
Keywords : Fabrication process ;Light emission;Porous silicon;Electroluminescence;Photoluminescene
Abstract : Recent observations of photoluminescene (PL) and electroluminescence (EL) from porous silicon (PS) have prompted many theoretical and experimental studies. Bulk crystalline Si is an indirect band gap material in which recombination is dominated by non-radiative processes. Therefore, it cannot be used as light-emitting component in Si circuits. PS is a new material formed by anodisation of single crystal Si wafers in hydrofluoric (Hi) solution. Luminescence from this material is being explored for technological applications all over the world. The mechanism of luminescence is still not well-understood. Several models have been proposed but still the facts about the strong light emission at room temperature are unknown. This paper presents a review of the fabrication process and studies on luminescent properties of PS. A hybrid model based on quantum confinement of carriers in the nanometer size Si crystallites having a large number of surface states is suggested to explain the observed properties. |
| | Identification of Helicopter Rigid Body Dynamics from Flight Data
Author : Chopra, A.K. ;Kumar, Ramesh;Chaudhary, K.L.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 69-86
Subject : 533.6 Aerodynamics;629.7 Aeronautics
Keywords : Mathematical models ;Aerodynamic parameters;Directional rigid body
Abstract : "This paper discusses helicopter modelling and identification related aspects. By applying the system identification methodology, longitudinal and lateral-directional rigid body helicopter dynamics are identified from flight data. Aerodynamic parameters from single input excitation as well as multimanoeuver evaluation are estimated utilising output-error approach. The formulated mathematical models yield adequate fit to measured time histories. Results obtained from the proof-of-match for model validation indicate that the identified derivatives can satisfactorily predict longitudinal dynamics to a given arbitrary input. It is further demonstrated for the present study that lateral body dynamics can be adequately predicted by including cross-coupling terms in the estimation model." |
| | Pyrolysis Caused Tail Off Thrust in a Solid Rocket Motor : A Semi Empirical Model
Author : Majeed, M.K.A. ;Sreekumar, K.P.;Ramachandran, N.;Madhava Panicker, P.R.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 87-91
Subject : 629.7 Aeronautics;629.76 Rockets and Missiles
Keywords : Polar satellite launch vehicle ;Semi empirical model;Solid rocket motors
Abstract : Knowledge of tail-off thrust characteristics of solid rocket motors used for an upper stage of satellite launch vehicle is essential for proper sequencing of stage separation. The phenomenon is highly complex and theoretical models accurately describing the tail-off thrust are not available. Only rough estimates can be made through ground testing. A semi-empirical model is derived by the authors using the Indian polar satellite launch vehicle (PSLV) flight data and is used for fixing the time of stage separation. The model has been validated using data over an extended duration from another flight of the PSLV. The method adopted for modelling is described. |
| | Some Issues relating to Design and Development of an All Composite Aero Gas Turbine Engine Rotor
Author : Gupta, K.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 93-98
Subject : 621.438 Aircraft Gas Turbine Engines
Keywords : Composite aero gas;Turbine engine rotor
Abstract : The paper addresses some of the issues involved in the development of an all-composite aero gas turbine engine rotor with a view to reducing the total engine weight and increasing the thrust-weight ratio beyond 20:1. It identifies the materials to be used for different components, i.e. shafts, discs and blades in the high and low temperature regions. The various problems anticipated in its development are discussed and solutions recommended, wherever possible. |
| | Lip Height and its Significance in Ballistic Studies
Author : Chopra, A.K. ;Kumar, Ramesh;chaudhary, K.L.
Source : Defence Science Journal ; Vol:48(1) ; 1998 ; pp 99-104
Subject : 623.4 Armaments and Ballistics;531.55 Projectiles
Keywords : Projectile;Ballistic parameters;Armour plates
Abstract : The mechanism of lip formation in steel armour plates has been investigated. Low alloy steel armour plates of 20, 40 and 80 mm thickness were impacted at zero incidence by steel projectiles of 6.l, 20 and 40 mm diameter, respectively at different velocities. The lip height was observed to exhibit definite correlations with other ballistic parameters like depth of penetration, crater volume, plastic zone and kinetic energy of the projectile. |
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