Defence Science Journal
Not a member yet
3794 research outputs found
Sort by
Influence of Resin Viscosity on Physical Properties of a Composite Shell Wound on a Low Density Material Mandrel
Full text linkThis study is made to improve the structural performance of composite shells/ vessels meant for aerospace vehicles. The effect of resin viscosity on the physical properties of carbon/ epoxy composite shell wound on polyurethane (PU) foam-based mandrel is studied and presented in this paper. Cylindrical shells were manufactured through the filament winding process at different resin viscosities. The physical properties of the composite shell are found to be improved significantly with a reduction in resin viscosity. Resin pick-up in impregnated fibers is found to be lower by 4.5 %, whereas mass and thickness of the shells are recorded to be lower by 3 % and 5.4 % respectively at resin viscosity range of 600 -760 mPa.s compared to the viscosity range of 1380 – 2080 mPa.s. Fiber volume fraction and density of composite shell are found to be higher by 6.3 % and 2.8 % at the same resin viscosity range. This trend reverses/stabilizes after further heating and corresponding lowered resin viscosity. Experiment and their result indicate an optimal viscosity range of 600 – 760 mPa.s. for filament winding of efficient carbon/ epoxy composite shel
Determination of the Reserved Gap Between the Obturator Ring and the Breechblock in the Metallic Obturation Mechanism of a Large Caliber Gun Howitzer
Full text linkA reserved gap between the obturator ring and the breechblock in the obturation mechanism of a large-caliber gun is required in the locked state of the gun, which is the main cause of gas leakage. In this study, the finite element analysis of the dynamic contact between the obturator ring and the breechblock and the computational fluid dynamics (CFD) analysis of the high-pressure gas flow through the gap between the obturator ring and the breechblock are conducted. The results show that the smaller the reserved gap is, the shorter the time period during which the contact pressure is zero after the obturator ring contacts with the breechblock will be under a low-bore pressure condition. The results also demonstrate that the leakage flow at the outlet of the gap and the gas flow in the external domain increase with the reserved gap size, and the gas flow in the external domain decays rapidly if the reserved gap is less than or equal to 0.02 mm under a high bore pressure condition. Based on the simulation results, the appropriate reserved gap value is determined and adopted in the studied gun, and good results are achieved in the firing tests
Novel Selective Maintenance Approach to Ensure Mission Reliability of Armored Vehicles Considering Multiple Deployment Roles in Distinct Operating Profiles
Full text linkGiven the gravity of the element of surprise in modern warfare, military forces worldwide are constantly attempting to achieve and maintain operational readiness of their critical military equipment. Selective Maintenance (SM) is considered an effective approach for achieving system operational readiness. Effective use of the SM approach for military equipment requires considering various military-specific factors such as multiple deployment roles, distinct operating profiles, human reliability, and the use of refurbished or non-OEM spares. This makes the SM approach for military systems very challenging. This paper presents an approach that formulates the SM problem intending to achieve and maintain the required level of operational readiness for predefined future missions from a military viewpoint. This approach employs a novel methodology that estimates the mission reliability of military equipment while modeling the combined impact of several important military-specific factors. This complex yet necessary integration of various military-specific factors makes the present approach accurate and apt to the exact modus operandi of the armed forces. The developed approach is demonstrated for the maintenance of armored vehicles deployed on distinct missions under different operating conditions. Numerical investigations illustrate the efficacy of the present approach and highlight its advantages over the conventional maintenance approach
Numerical Study on Mixing Characteristics of Circular and Non Circular Jets
Full text linkThe study of non-circular jet flows has become important due to their various applications such as aircraft exhaust, combustion chambers and injectors. The goal of present paper is to examine the impact of elliptical, square, and triangular shaped orifices on the mixing characteristics of a free jet with Mach number 0.8. Numerical simulations using an SST K-ω two-equation turbulence model were conducted with a Reynolds number of 3.46×105 for all cases. The mean velocity, decay rate, half-velocity width, spread rate, and turbulence intensity of the jet were analysed. The results showed that the triangular orifice provided the best mixing efficiency, with a shorter jet core length. The decay rate was found to be lowest for the square jet and highest for the triangular jet, which matches with the previous research. The asymmetric jets experienced two axis-switching points, while the square jet experienced a 450 rotation of its axes but no axis-switching. The core region had lower turbulence levels, while the highest turbulence levels were in the shear layer
Performance Estimation by Varying the Grain Port Alignment Position in a Hybrid Rocket Motor
Full text linkA Hybrid Rocket Motor (HRM) is a type of chemical rocket propulsion in which the propellants are stored in different physical states. To counter the low regression rate characteristic of HRM different grain configurations with innovative port techniques has been evolved with time. It creates better mixing and combustion of fuel with oxidizer without having any special injector and energetic additives. A similar technique has been used in the present study. The fuel used in the present study is a solid grain made from polyvinyl chloride with di-butyl phthalate in the 50:50 ratios with gaseous oxygen as an oxidizer. In this paper, analyses are made to study the performance of a hybrid rocket motor by varying the axial alignment of the grain port at varying locations along the length. Due to the offset of the fuel port at varying locations, recirculation zone were created that enhanced the pressure in the combustion chamber by around 1-2 bar. The thrust generated was increased in the range of 10 to 25 N. Regression rate as well as efficiency was also observed to be increased with the use of this port alignment techniques
Impact of Solid Rocket Propellant Grain Manufacturing Limitations on Launch Vehicle Capability
Full text linkIt is examined if any limitations in existing solid rocket propellant grain manufacturing methods adversely affected the payload capability of recent space launch vehicles. It is seen if the transition from heavy, segmented metal rocket motor casings to lightweight monolith composite casings is possible without loss of ability to design and realize high-performance grain configurations using simple and safe methods. Considering payload fraction as the comparative performance metric, recently flown solid rocket-propelled, small-lift launch vehicles were surveyed and ranked. Solid rocket boosters of underperforming launch vehicles were investigated for manufacturing factors influencing payload fraction by comparing them to boosters of better-performing launch vehicles in their weight class. Relationships between payload fraction and the solid boosters’ mass fractions, casing construction, shape of thrust profile, propellant grain configuration and method employed to manufacture the grain were analysed. It is shown that those launch vehicles that did not possess or use the technology necessary to manufacture high-performance grain configurations like undercut finocyl in monolith composite casings ended up having boosters delivering poor thrust profiles with high inert mass ultimately leading to low payload fractions
Prediction of Mechanical Response of Nickel based Superalloy Subjected to Creep Fatigue Interaction Loading using Unified Mechanics Theory
Full text linkIn order to simulate and predict material's real-time responses for a component under complex mechanical and thermal loads, continuum damage mechanics (CDM) is employed. However, majority of the models found in the literature are phenomenological and primarily based on curve fitting, which offer limited understanding of the underlying physics of the problem. A few physics-based models have been developed that provide greater insights. Unified mechanics theory (UMT) is one such approach that captures entropy generation due to various dissipative mechanism which aims to explain the physics of the problem. During hold time in strain-controlled creep-fatigue interaction loading, stress relaxation is observed. This study attempts to capture stress relaxation response due to creep-fatigue interaction of nickel-based superalloys using UMT, which is regarded as a more scientific method than simply fitting curves. The evolution of creep strain energy with hold time is used to understand how material ages over time due to stress relaxation during creep-fatigue interaction loading
Advances in Solid Mechanics and Composites
Full text linkApplied mechanics is a scientific discipline that focuses on the study of various laws of mechanics and their application in solving engineering problems. The Indian Society for Applied Mechanics (ISAM) organizes conferences focused on various areas of applied mechanics, encompassing solid mechanics, fluid mechanics, and biomechanics. The fifth Indian Conference on Applied Mechanics (INCAM-2022) was jointly organized by the Department of Mechanical Engineering, National Institute of Technology (NIT) Jamshedpur, and ISAM during November 11-13, 2022 at Jamshedpur in India. It provided a technical platform for researchers and academicians to present their research work and discuss the broad field of applied mechanics........
The Investigation of KH560 Coupling Agent with Carbon Fiber One Step Dipping Method Compared with Functionalized Multi Walled Carbon Nanotubes
No full textInterlaminar and interfacial properties of composites are important parameters for any application, extensive research has been out bursting to enhance the above properties using nanotubes (NTs) as an alternate solution to minimize delamination of laminates. This research focused on significance of functionalized engineering materials for better efficiency in industries, especially stealth technology. Silane-coupling agent “3-glycidyletheroxypropyl-tri methoxy silane, KH-560” is one module among five modules designed in this work. Five modules are considered as (M1, M2, M3, M4 & M5) with (0.5wt% of AMINE, CARBOXYL, multi wall carbon nano tubes (MWCNTs), 5% KH-560 treated carbon laminate and finally with base carbon fiber). PAN-based 12k carbon fiber as base fiber with functionalized and non-functionalized nanocomposite are incorporated as fillers in the epoxy laminates fabricated using vacuum bagging technique. Findings indicated 5% KH-560 silane treated carbon fiber (module M5) showed best results such as properties with 39%,55% and 20% in “tensile, flexural and interlaminar shear strength (ILSS)” respectively. FESEM analysis is conducted to understand morphology of the laminates
Experimental and Numerical Investigation of Bodywork Effect on High Hardness Armour Steel Against a 7.62 x 51 mm NATO Ball M80 Projectile
Full text linkSmall arms ammunition like the 5.56×45 mm NATO Ball and 7.62×51 mm NATO Ball projectiles constitute a significant threat to light armoured vehicles. These vehicles are mostly comprised of single-layered metallic high-hardness steel armour, but as an essential vehicle design feature, mild steel bodywork is externally mounted in certain areas for fenders, toolkit boxes, storage boxes, etc. over the main armour, i.e., high-hardness steel armour. These are necessary design features of vehicles, so they can’t be neglected regarding ballistic protection against threats. Also, to provide better ballistic protection in up-armoured vehicles, armour consisting of high-hardness steel armour is integrated or mounted just behind the existing bodywork of the car. Thus, this paper experimentally and numerically investigated the “bodywork effect,” which is also called the “K-effect,” and found that the configuration where the bodywork of mild steel is placed in front of high-hardness steel armour plate failed to provide better ballistic protection against the 7.62×51 NATO Ball M80 projectile fired at 0° angle of impact with a velocity of 833±20m/s from 10 m distance. However, the single high-hardness armour steel plate provided better ballistic protection than the configuration consisting of bodywork. For the validation of the experimental investigations, the arrangements were numerically simulated. The main aim of this work was to check the bodywork effect against this particular projectile and investigate factors contributing to the phenomenon