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Research Activities

Design and Analysis of Nose Cap Structure for Advanced Reusable Launch Vehicle

The nose cap of the advanced reusable launch vehicle is designed with materials that are lighter in weight and that can withstand the severe flight conditions.  Two design with Inconel 718 alloy and carbon-carbon composite as materials are studied.  Aerodynamic heating rates and loads on nose cap are estimated and shell thicknesses for nose cap are arrived at based on 3D transient thermal analysis and preliminary structural analysis.  Fasting mechanism to integrate nose cap with vehicle fuselage front-end ring is configured.  Thermal response analysis, thermo structural analysis, buckling and modal analyses are carried out using FEA.

Quality Assessment of Products using Resonance Inspection Technique

            Resonance Inspection, a non-destructive evaluation technique that uses natural resonances of a part to identify non-conforming parts, is used to characterize cracks with different depths and location on a cantilever beam.  Finite element modal analysis results are compared with the experimentally obtained values using an impact hammer and LabVIEW software. Further, inspection of defective and non-defective geometrically identical gears reveals that the resonance inspection technique can indeed be used to separate non-conforming parts.

Inharmonicity of Wound Guitar Strings

            A detailed study is done regarding the reduction of inharmonicity by the use of round-wound strings.  A theoretical model of plane string with certain approximations is used to successfully model the inharmonic characteristics of the wound string.  The observations were validated by measuring the vibrations of the wound string and comparing it with the theoretical values.  A comparison is made between the wound string and plane string with equivalent density, and the resulting reduction in inharmonicity is quantified.

Low Frequency Vibration Analysis on Passenger Car Seats

            In order to ascertain the seating dynamics and dynamic comfort of a car seat, the change in transmissibility under varying passenger weight and terrains is evaluated.  From the acceleration data, the ride comfort index is found and analyzed.  The biological impacts on the passenger due the vibrations at various frequencies are identified.  The variation of transmissibility with passenger weight and different terrain roads is studied on four different makes of passenger cars.

Crash Simulation in ANSYS LS-DYNA to Explore the Crash Performance of a Car

            A simple finite element model of a car is developed in ANSYS and it is solved for full frontal impact in ANSYS LS-DYNA explicit code.  Computational simulations and various results are plotted and analyzed.  It is observed from the analysis that composite materials absorb almost the same amount of energy as the metallic materials in a car crash, with the former having an added advantage of light weightiness in automobiles.

Evaluation of Precision Angular Contact Ball Bearings using Vibration Spectrum

            The aim of the work is not to identify defects in precision angular contact ball bearings used in reaction wheels which serve as actuators for attitude control of satellites.  The condition of bearings with respect to parameters like pre-load, lubricant quantity and condition of the retainer was assessed.  These factors are evaluated under various experimental conditions and their vibration spectrum is obtained and evaluated. The vibration signature is acquired using an accelerometer and then evaluated using MATLAB program. This program is used to generate the spectrum from the acquired signal and then annotate various characteristic bearing frequencies, harmonics and sidebands.

Kinematic Analysis of Crew Module Hatch Door Hinge Mechanism

            In order to take humans to low earth orbits and bring them back safely, the orbital vehicle used is called the Crew Module.  A hatch is required for the safe entry and exit of the crew in to and out of the crew module. The mechanism of the hatch is such that it should provide a linear travel for the hatch door in the radial outward direction to take care of the hatch thickness and to prevent any damage to thermal protection system overlay and crushing of pressure seals. The mechanism given is a six bar multi loop single degree of freedom mechanism. The mechanism was split up in to two loops forming two four bar mechanisms. Each loop was analyzed separately using loop closure equations.  

Design and Analysis of Vibration Isolator for Launch Vehicles

            The launch vehicle has many critical subsystems like electronic packages which are sensitive to induced vibration in flight.  Therefore the avionics and Pyro system mountings which are to be assembled to these structures are to be properly isolated from the random vibratory excitations. Vibration isolators are used in launch vehicles to protect these sensitive equipment components from dynamic disturbances such as vibration and shocks during launch and flight. Silicone rubber is used as isolators in these applications due to their excellent chemical and environmental resistance, good damping properties, easy compound modification and good ageing characteristics. This work outlines the modifications carried out on present isolator design to improve its stiffness.

Numerical Simulation of Residual Stress in Double Sided Arc Welding

            Simulation of double sided arc welding process can help to predict the residual stress, distortion and other factors which greatly affect the production process. The determination of residual stress during DSAW process and the distortion produced require several experimental and practical knowledge of the physical scenario. Numerical simulation technique can be used in such situations so that the optimum welding parameters can be used in the production process without prior experimentation.  In this process, part of the welding current will flow through the keyhole established through the thickness direction and maintain the electric arc inside the keyhole. The current in the thickness direction and the establishment of a keyhole helps to enhance the concentration of the arc and the density of the arc energy.

Study of Interlaminar Shear Stress of Composite Structures

            An appropriate evaluation of inter-laminar shear stress leads to an accurate prediction of failure, which is a challenging task for researchers and analysts.  The present study focuses for the determination of inter-laminar shear stress in composite structures. The direct approach to predict inter-laminar shear stress using solid element is computation-intensive. Layered shell elements are used for relatively thin structures. Layered solid element is used for thick structures but it has its own limitations.  The present study provides an analytical method to determine the inter-laminar shear stress of composite structures using graded mesh with solid element through Finite Element Analysis software ANSYS.

Design/Analysis of a Progressive Tool for Blanking of a Component - Optimal Approach

            The progressive tool is a type of press tool that produces one finished blank per stroke of the press. Depending on the complexity of the part to be produced, it is split up into a number of simple parts and the work is completed sequentially at a number of stations.  Several strip layouts are drawn and the one with high strip utilization factor is selected. Centre of pressure is calculated after effective distribution of punches is done for blanking. Then calculations for force, dimensions of plates, design of spring, dowel pins, screws etc., are performed.  After careful observation at every stage of design, proper remedial actions are taken and the design is optimized in every aspect.

Analysis of Hydraulic Brake System Actuated Using Elliptical Rolling Contact Joints

            Elliptical rolling contact joints in compression are introduced as an alternative to circular rolling contact and conventional revolute joints where high quality force transmission, low friction and backlash, with variable output are desired. Parameters specific to the joint and its position are defined in terms of relative link angles and elliptical surface geometry. Elliptical rolling contact joints are shown to offer several benefits over circular rolling contact, including reduced Hertz contact stresses, variable output velocity, maximum use of contact interface by distributing small rotations across surfaces of small curvature, reduced forces on constraining members, and no-slip pure rolling provided by either connecting links or flexures, without the need for gear teeth or friction. To prove the advantages of elliptical rolling contact joints a working model is created in which a hydraulic brake system is actuated by using an elliptical rolling contact kinematic chain.

Vibration Response of Tensioned Vibration Isolation Module with Nylon Strength Member

            Vibration isolation modules (VIMs) are used in underwater towed acoustic sensor arrays to control mechanically induced tow noise. VIMs are introduced on either ends of the hydrophone arrays to reduce the vibrations and consequently the mechanically induced noise. The three major components of VIM i.e., Nylon strength member, hose and gel are polymers. The study includes material characterization of Nylon, estimation of longitudinal vibration response by finite element method and experimental validation.  The viscoelastic model for VIM is developed using discrete parameter models, and comparison is done between three and five parameter models. The longitudinal vibration response is estimated using finite element method for three progressive stages of assembly and subsequently validated experimentally.

Design of Haptic Exoskeleton for Human Arm

            The design, fabrication and evaluation of a four degree of freedom force-reflecting haptic interface are performed.  Haptic interface is defined as a kinesthetic link between a human operator and a virtual environment. The user's arm is strapped in to the device, which allows him/her to interact with surfaces and objects created in a virtual environment. The device provides the necessary force feedback allowing users to 'feel' objects within the environment. The device works extremely well, as users are able to differentiate between different weights, rough and smooth surfaces and between object size and surface stiffness. The potential applications for this device include virtual object manipulation, medical rehabilitation, tele-manipulation and training.

Analysis of Dynamic Behavior of Pre-Stretched Circular Hyper-Elastic Membrane

            Dynamic analysis of the linear vibration response of a pre-stretched circular hyper elastic membrane with large deformation is performed. Geometrical as well as material nonlinearity come together due to finite deformations and a hyper elastic constitutive relationship. The membrane material is assumed to be isotropic, homogeneous, and Neo-Hookean. A commercial finite element code ANSYS is used to perform the prestressed modal analysis as well as hyper elastic material curve fitting.  The effect of stretching ratio and membrane thickness on the mode frequencies, shapes and order is studied. The increase in stretching ratio increases the concentration of in plane modes in the lower frequencies, and also decreases the frequency of the same. The out of plane modes are dominant in the lower frequencies at lower stretch ratios due to the predominance bending stiffness compared to membrane stiffness.

An Assessment of Energy Absorption Capability of Honeycomb Core

Honeycomb is a light weight, high performance to mass ratio structure with high energy- absorbing capability. Because of the presence of the honeycomb core, energy absorption capability increases and hence it has been widely used in aerospace structures to resist impact loads. In the present study, which explores the energy absorption capability of honeycomb structure, a cartridge made of aluminium honeycomb core is designed, fabricated and drop tested for a launch vehicle programme in ISRO. Aluminium honeycomb core is used as an excellent energy absorber while being axially crushed. The honeycomb crushes under load in a uniform way, preventing damage to the supporting structure.  Finite element analysis is carried out using ANSYS LS-DYNA, simulating the honeycomb core cartridge in experimental conditions. The result is validated by the experiment conducted in HPDD Lab, ISRO.

Parametric Study of Lattice Conical Adaptor

Grid structures are characterized by a lattice of rigid, interconnected ribs. These are fabricated with or without skins depending upon the applications. The ribs that comprise the structure can be arranged in a variety of ways. Generally the ribs are arranged in axial, circumferential and helical directions.  Unidirectional arrangement of the ribs possesses good impact damage tolerance, resistance to delamination and crack propagation across the grid. The ribs comprising the grid structure are usually loaded in axial direction so that in composite grid structure fibers are usually oriented along the ribs axial direction to provide axial strength and stiffness. The main advantages of the grid structure are its stable configuration, higher structural efficiency and lower cost.