PhD Theses (Mechanical Engineering)

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(A) Fuzzy Set Based Setup Planning Expert System Considering Fixturing Aspects for Machining of Prismatic Parts
(2010) Hazarika, Manjuri
Systematic determination of the steps to convert a raw stock to a finished product is an important issue in manufacturing. It is the task of process planning to translate the design information of a part into manufacturing instructions. Process planning can be decomposed into several sequential phases, viz. design interpretation, process selection, setup planning, tolerance assignment, process parameter selection, and documentation [Xu et al. 2007]. Setup planning constitutes the core of a process planning system. Setup planning is the part of process planning concerned with the grouping of features into setups in their proper sequence, selecting datum for each setup, sequencing the setups and choosing appropriate machines, tools and fixtures. As manual planning is tedious and time consuming, efforts to automate process planning and setup planning have been going on since 1980s [ElMaraghy, 1993; Eversheim and Schneewind, 1993; Leung, 1996; Yip-Hoi, 2002; and Xu et al., 2007]. A feasible and optimal setup plan involves a number of constraints that are mutually conflicting considering technological, geometrical and economical aspects of both design and manufacturing domain. Nevertheless, the ultimate goal of automating setup planning is to achieve the desired quality of the finished product at the lowest possible production cost and with the minimum manufacturing time.
(A) graphite particle-filled viscoelastic composite layer for active/passive constrained layer damping treatment of structural vibration
(2021) Gupta, Abhay
In this dissertation, a viscoelastic particulate composite (VEPC) is proposed for the improved constrained layer damping (CLD) treatment of structural vibration/dynamic instability. This VEPC is comprised of micro-sized graphite particles that are dispersedly distributed within the Butyl rubber matrix. The effective material properties of this VEPC are estimated using a differential scheme and the elastic-viscoelastic correspondence principle. The corresponding results reveal increased effective storage modulus and decreased effective loss factor of a viscoelastic medium for the inclusion of graphite particles. With these material characteristics of the VEPC, its damping capability is investigated in the active/passive constrained layer damping (ACLD/PCLD) treatment of the structures such as beams and plates. Further, the study on the VEPC based ACLD treatment is carried out using either extensional or shear mode piezoelectric actuators. The analysis in each of the PCLD and ACLD cases is performed using finite element procedure. The results reveal that the inclusion of graphite particles not only causes an improved transfer of active action from the piezoelectric actuator layer to the substrate layer but also enhances the energy-dissipation capability of the constrained viscoelastic layer. Therefore, the passive, active and active-passive damping in the structures increase significantly for the inclusion of graphite particles within the viscoelastic damping layer. However, there is an optimal volume fraction of graphite particles in the VEPC damping layer for the maximum damping capability of the PCLD/ACLD treatment. Besides, a new strategy in passive control of parametric instability is introduced by the use of the constrained VEPC layer, where the instability region not only reduces but also shifts aside from the operating frequency range depending on the volume fraction of inclusion in the VEPC layer. Endmost, the performance of the present VEPC layer in the CLD/ACLD treatment is compared to that for an existing viscoelastic composite by the name of 0-3 viscoelastic composite. The overall study in this thesis presents a novel viscoelastic particulate composite layer for the improved CLD/ACLD treatment of structural vibration.
(A) Numerical and experimental investigation of the mitigation of unbalanced magnetic pull in a bridge configured induction machine
(2019) Sivaramakrishnan N
An eccentric rotor position produces unbalance in the field and generates a net radial force called unbalance magnetic pull (UMP). The magnitude and direction of this UMP mainly depends on the degree and type of the eccentricity. This UMP can severely degrade the performance of the machine, causing noises and vibrations. A built-in force actuator has been used to generate an additional force on the rotor for controlling the vibrations. The present work proposes a specialized winding scheme called Bridge-Configured Winding (BCW) which is a single set of winding which can be able eliminates the drawback of the dual set of winding. The main objective of this present work is to develop an experimental rig set up for an active vibration control in a three phase, four pole induction machine. The UMP occurs in the induction machine mainly due to the distortion in the air gap magnetic field. So, it is important to maintain the uniform flux density distribution in the air gap.In order to achieve this, a bridge configured stator winding has been incorporated in a 37 kW three phase induction machine. This special kind of bridge configured stator winding provides an external, isolated power source apart from the main supply source which will be able to mitigate the UMP. This work aims to control the rotor vibration passively as well as actively.To demonstrate the active vibration control of the rotor, a controller has been developed. The controller can provide the three phase isolated power supply to the system as an external source. The experimental results will be compared with the numerical results.
(A) numerical investigation on augmented heat flux in non-standard variants of turbulent Rayleigh-Bénard convection
(2023) Chand, Krishan
The present work investigates non-standard variants (roughness-aided and tilted convection) of Rayleigh-Bénard convection (RBC) to augment heat flux for a fixed working fluid (Prandtl number = 0.7) over a wide Rayleigh number range (106 ≤ Ra ≤ 1010). For both 2D and 3D, the study focuses on the coherent structures and heat transfer mechanisms in different configurations of Rayleigh-Bénard convection (RBC), considering thermal plumes, boundary layers, and large-scale rolls (LSR). In the smooth case, the absence of lateral direction results in the entrapped thermal plumes, which are subsequently emitted as thermal jets into the bulk. The Nusselt number (Nu) quantifies the heat carried by thermal plumes across the isothermal walls. A positive correlation between vertical velocity and temperature fluctuations is used to quantify thermal plumes. The impact of surface roughness on heat flux is investigated, highlighting the influence of irregular roughness geometries. The study identifies an onset of enhanced heat flux regime and explores the role of bulk-plume interaction and fluid mixing. With increasing Rayleigh number, transformation from a double-roll state to multiple-roll state is associated with the onset of enhanced heat flux regime for the taller configuration. On the other hand, presence of huge number of roughness elements is responsible for enhanced heat flux in the smaller configuration. Near-wall dynamics and the penetration of peaks into the thermal boundary layer are studied, revealing the significance of secondary vortices and the tendency of plume emission. The investigation extends to three-dimensional RBC with conical roughness configurations, emphasizing the role of coherent structures and intense thermal plumes in enhancing heat flux. The study provides insights into the influence of roughness on flow strength and the orientation of large-scale rolls. The effect of inclination angles in tilted RBC is examined, indicating shifts in heat transport effectiveness and early onset of turbulence with increased roughness height. In the smooth case, inclined convection (IC) enhances heat flux below Ra = 108, while above this value, normal RBC yields the highest heat flux. However, for rough surfaces, the effectiveness of IC to transport heat shifts to lower Ra as the roughness height increases, leading to an early onset of turbulence. The maximum heat flux in the smooth case is achieved at a tilt of 75° for Ra ≤ 108, while in roughness cases, it depends on both Ra and the roughness configurations. The study reports a maximum increase of 25% in Nusselt number for roughness-aided tilted convection. Additionally, as Ra increases, the onset of thermal stratification is delayed in the smooth case, while an increase in roughness height results in a similar delay in rough configurations, indicating an early onset of turbulence even at larger inclination angles.
(A) Study on end forming of metallic tubes
(2019) Agrawal, Arvind Kumar
End forming of tubes generally refer to making of simple or complex shapes such as expansions, reductions, flares, flanges, tapers, and beads made at the end of the tube by single or multiple metal forming operations. These end formed tubes have plenty of applications in our day-to-day life, agriculture and automobile sectors. Earlier research in the field of tube end forming was focused on identification of main process parameters, especially tube inversion methods. With the further advancement of tube end forming technology some innovative methods of joining involving tube end forming have been proposed and it was observed that joint strength of end formed joints is at par with the joints obtained from conventional methods.
(A) Theoretical and Experimental Study of Thermal Autofrettage Process
(2016) Kamal, Seikh Mustafa
Thick-walled cylinders/hollow-disks find wide range of industrial applications to withstand very high pressure. Pressure vessels, gun barrels, fuel injection system in diesel engines, nuclear reactor and fastener holes are the typical examples. The cylinder may crack if the working internal pressure exceeds the yield strength of the material. The pressure carrying capacity and fatigue life of the thick-walled cylinders used for high pressure application can be significantly improved by inducing beneficial compressive residual stresses at and around the inner wall of the cylinder. This is achieved by employing a process called autofrettage, prior to their use in service condition. The most commonly employed autofrettage processes are hydraulic and swage autofrettage process. The hydraulic autofrettage is achieved by pressurizing the cylinders to an ultra-high hydraulic internal pressure. The swage autofrettage is achieved by pushing an oversized mandrel through the inside of the cylinder to plastically deform the inner wall and some portion beneath it. The autofrettage can also be achieved by detonating an explosive charge inside the vessel, which is called explosive autofrettage. All these existing processes have certain disadvantages. In order to avoid the difficulties associated with the existing methods of autofrettage, in the present thesis, a thermal autofrettage process is proposed. The proposed thermal autofrettage process is achieved by creating a radial thermal gradient across the wall thickness of a cylinder or hollow disk. The proposed thermal autofrettage process is very simple and easy to handle compared to the existing methods of autofrettage.
Active control of annular plates through the design of extension/shear mode pfc actuators
(2018) Kumar, A. Srinivas Pavan
This dissertation deals with the active control of flexural vibration of annular plates through the design of two new piezoelectric fiber composite (PFC) actuators in the cylindrical coordinates. The first one is an extension mode PFC actuator, and the next one is a shear mode PFC actuator. The extension mode PFC is basically a cylindrically orthotropic short piezoelectric fiber composite (SPFC) in the shape of a thin annular disc. This annular SPFC disc is comprised of unidirectional short piezoelectric fibers embedded in the epoxy matrix. The longitudinally poled short piezoelectric fibers are oriented in the radial direction so that the extension mode piezoelectric actuation appears along the radial direction in response to an externally applied coaxial electric field. The effective electro-elastic properties of this SPFC actuator are estimated by developing a finite element (FE) procedure, and the changes in the properties due to the use of unidirectional short/discontinuous fibers (SPFC) instead of the continuous fibers (CPFC) are demonstrated. A fruitful arrangement of surface-electrodes over the top and bottom surfaces of the annular SPFC/CPFC disc is proposed, and its (SPFC/CPFC) actuation capability is investigated in active control of harmonically excited flexural vibration of an annular substrate plate.
Aerodynamic drag and lift characteristics of a newly developed elliptical-bladed savonius wind turbine rotor
(2019) Alom, Md. Nur
The elliptical-bladed rotor that has shown its potential to harness wind energy more efficiently is considered for the present numerical and experimental studies. In the present investigations, initially 2D unsteady simulations have been conducted for the elliptical, modified Bach, Benesh and semicircular profiles of the Savonius rotor. This is to check and corroborate the past research findings. The geometric parameters such as overlap ratio, number of rotor blades and effect of shaft are then considerd. The unsteady simulations are also carried out to analyze the influence of Reynolds number on the rotor performance. Thereafter, unsteady simulations are carried out by implementing the vent-augmenters. The CD and CL of the elliptical-bladed rotor is evaluated and compared with that of a semicircular-bladed rotor. TThe average CD for a complete rotation of elliptical and semicircular profiles are found to be 1.43 and 1.35, respectively. Hence, there is higher average CD by 6% in the elliptical profile than the semicircular profile. Further, the CL and CD are also estimated for the modified Bach and Benesh profile to have a comparison in a common platform. The 3D unsteady simulations are then conducted to estimate the performance coefficents (CT and CP) and aerodynamic coefficients (CD and CL) of vented elliptical bladed rotor.Subsequently, the wind tunnel experiments are conducted to validate the numerical results. The wind tunnel tests show the peak C P to be 0.19 and 0.15 for the elliptical bladed and semicircular bladed rotors, respectively at TSR = 0.7 and AR = 1.09. Hence, there is an improvement of C P by 27% in elliptical bladed rotor than th e conventional semicircular bladed rotor.Finally, the multi-objective genetic algorithm (MOGA) has been applied to the optimized elliptical profile to minimize the incoming velocity and to obtain the maximum torque and lift coefficients. From the MOGA, the elliptical profile shows the CP to be 0.35 at V = 5.91 m/s (at TSR = 0.80). At the same TSR, the semicircular profile shows the CP to be 0.28 at V = 6.06 m/s. On the other hand, the unsteady numerical simulation at V = 6.2 m/s shows CP = 0.34 and 0.27 for the elliptical- and semicircular profiles, respectively.
Aerodynamic Performance Evaluation of a Novel Savonius0Style Wind Turbine Through Unsteady Simulations and Wind Tunnel Experiments
(2014) Roy, Sukanta
Recent instabilities in the world energy market due to depletion of fossil fuel source, global worming threat and increasing price of fossil derivatives necessitate the need of harnessing the clean and renewable sources of energy.
Aerothermodynamic Analysis of Flow Modification Techniques in Non-equilibrium Supersonic/Hypersonic Flows
(2021) Kumar, Shailendra
Higher wave drag is a common problem for an object flying in the supersonic or hypersonic flow regime. Hence, the present investigations use computational fluid dynamics as a tool to study the dynamics of flow field to mitigate the adverse effects in such a complex environment. For this, a finite volume-based two dimensional axisymmetric compressible reacting flow solver is developed which is comprised of five species and eleven chemical elementary reactions. Initial investigations on blunt object show that downstream movement of the bow shock and shock stand-off distance lead to increases in the surface pressure and thus drag force. Shock reconstruction for the spiked object leads to the downstream movement of the conical shock which leads to the lesser size of recirculation zones. Hence, higher pressure and drag is obtained for every shapes of spike (Conical, spherical and flat) length at higher stagnation enthalpy cases. Integration of two drag reduction methods, spike and counter flow jet, is also proved a better drag reduction device. Further, studies are carried out to understand the Shock-Shock (S-S) interactions for a spherical object in the presence of a forward-facing stagnation spike. The shock stand-off spike (L=0.125D) witnesses initiation of the S-S interaction and seeding of a recirculation zone. This is the spike case at which frictional drag is higher than the wave drag. Further longer spikes alter the recirculation bubble size and S-S interaction type. Stronger interaction and undeveloped recirculation, for spike length of 0.25D, lead to maximum drag enhancement for the object. Higher exergy destruction is also observed for the same spike length. Further increment in spike length produces weaker interaction as well as larger recirculation zone which improves drag reduction for the same object. Combination arrangement of spike (L=0.25D) and counter-flow jet is also investigated to prove that at least two recirculation zones and weak S-S interaction are mandatory for the realization of drag reduction using a stagnation spike. Unsteady single pulse energy deposition at higher freestream enthalpy show increase in pressure and decrease in density in the deposited energy pulse. Moreover, the size of the blast wave increases for elevated enthalpy cases. This alteration in energy pulse leads to the formation of a stronger vortex in the stagnation region and witnesses generation of an extra valley in the drag signal. Hence, power effectiveness for the energy pulse increases at higher enthalpy conditions and it is in consistent with all upstream deposition locations. Further, steady energy deposition is marked with higher drag and lesser power effectiveness at higher stagnation enthalpy conditions. Hence, the unsteady energy deposition is found to be better for drag reduction over the steady energy deposition at higher enthalpy cases. Performance of unsteady energy deposition has shown further improvement when multiple pulses are deposited in a certain frequency at a given upstream location.
(An) Accurate and Efficient Varying Order NURBS Discretization Method for Isogeometric Analysis of Contact Problems
(2021) Agrawal, Vishal
In this work, a new varying order based NURBS discretization is proposed to enhance the performance of isogeometric analysis (IGA) technique within the framework of computational contact mechanics. The proposed method enables the order elevation based refinement of a NURBS discretized geometry in a controlled manner. It allows the usage of higher order NURBS functions only for the evaluation of contact integrals. The minimum orders of NURBS capable of representing the complex shape geometries exactly are employed for the bulk computations. To achieve this, a higher-order NURBS layer is used as the contact boundary layer of an initially lower-order NURBS discretized geometry. The NURBS layer is constructed using different surface refinement strategies such that it is accompanied by a large number of additional degrees of freedom and matches with the bulk parameterization. Further, a Gauss-point-to-surface contact algorithm with the penalty method is combined with the presented methodology towards developing a simple yet computationally efficient technique for isogeometric contact analysis. In order to demonstrate the efficacy and capabilities of the proposed method, various numerical examples involving small and large deformation contact between deformable bodies in two- as well as three-dimensional settings with or without accounting friction are considered. In addition, an adhesive peeling problem is analyzed to demonstrate its performance for the peeling computations. The results with the existing standard NURBS-based discretizations are used for the comparative assessment. The obtained results show that with the proposed method, much higher accuracy can be achieved even with a coarse mesh as compared to the existing NURBS discretization approach. It exhibits a major gain in numerical efficiency without the loss of stability, robustness, and the intrinsic features of the NURBS-based IGA technique for a similar accuracy level.
Analysis and Identification of Dynamic Transmission Error Parameters in a Geared Rotor Using Full Spectrum
(2023) Rao, Bhyri Rajeswara
Geared rotor bearing systems are widely used torque carrying components in most of the mechanical and electrical equipment in the automotive, aerospace and ship building industries. A dominant source of vibration in geared rotor systems are the gear mesh dynamic transmission error (TE) parameters. These include the static TE, the mesh stiffness and damping, and the gear runout. One needs to know additionally these dynamic parameters along with the gear macro-geometry (for examples, the number of teeth, pitch circle diameter, pressure angle, and tooth geometries), load and rotating speed, for the vibration-based diagnosis of geared rotor power transmission units.
Analysis and scaling of coupled neutronic thermal hydraulic instabilities of supercritical water-cooled reactor
(2018) Shankar, Daya
Present thesis work primarily focuses on the analysis of flow instabilities in one of the most powerful concepts under Gen.-IV nuclear reactor technology, namely the supercritical water-cooled reactor (SCWR). Safety is the primary concern in nuclear reactors and the study of flow instabilities is an important aspect of safety assessment. To facilitate the study of complex phenomena in the laboratory, a method for designing a downscaled model has been proposed here for both natural as well as forced circulation SCWR. For detailed analysis of the stability characteristics of the system, a simple but computationally inexpensive model has been developed as lumped parameter model (LPM). Using this model, linear and nonlinear stability analyses have been done for various ranges of parameter values. Instabilities in SCWR subjected to seismic effects have also been analysed by using the LPM.Nuclear power plants use the heat generated from nuclear fission in a contained environment to convert water to steam, which powers generators to produce electricity. Light water reactors (LWR) use water as coolant and moderator. SCWR is a Gen.-IV LWR. It is a concept for an advanced reactor that operates at supercritical pressures and temperatures (25–30 MPa, 500–520 oC exit temperature). Such a high coolant temperature at turbine inlet provides high thermal efficiency (~42%) which is substantially greater than any other LWR (~30%). Consequently, it also experiences significant density difference throughout the coolant channel, from the inlet to the outlet (720 kg/m3 to 90 kg/m3), which raises grave concerns about flow instabilities in the SCWR. To ensure a proper design of SCWR without any safety issues, detailed stability analysis over wide parameter ranges is needed.
Analysis of free surface flows in formation, coalescence and impact of drops on liquid surfaces
(2018) Deka, Hiranya
The dynamics of free surface flows have been of great interest to researchers for centuries because of its applications in a variety of industrial processes and due to the richness of the underlying physics. The present thesis is focused on the numerical study of free surface flows in context with formation and coalescence of drops. The numerical simulations have been performed by solving the complete Navier-Stokes equations and the interfaces have been captured using the coupled level set and volume of fluid (CLSVOF) method. The drop formation from an orifice has been studied with an emphasis on the resulting drop’s shape after pinch-off. The oscillatory motion of the drop after pinch-off has been investigated. During the impact of a drop on a liquid pool a range of fluid dynamical phenomena can be observed including drop coalescence, drop splashing and bubble entrapment. Here, the large bubble entrapment phenomena has been thoroughly studied to unveil the mechanism of large bubble entrapment. The regime of large bubble entrapment has been identified on the on impact velocity (V ) - drop diameter (D) map and on the Froude number (Fr)-Weber number (We) map. The satellite generation during the coalescence of two unequal sized drops has been studied. Furthermore, investigations are performed on the impact of a high-speed train of microdrops on a deep liquid pool which produces a deep tongue shaped cavity. The dynamics of this tongue shaped cavity has been investigated in detail and are reported in this thesis.
Analysis of Stability and Unbalance Response of Flexible Rotor Supported on Hydrodynamic Porous Journal Bearing
(2010) Laha, Swarup Kumar
Rotating machines are one of the most important and widely used machineries in modern engineering world. Now-a-days modern rotating equipments have a number of complicated accessories attached with it and they are also made extremely flexible. They are also required to run at higher speed, much higher than their first critical speed. Fluid-film bearings supporting the rotating shafts play an important role in the dynamic behaviour of the rotors because of their stiffness and damping properties. Hydrodynamic bearings are one of the most widely used bearings to support the rotating shafts. Rotor-bearing systems exhibit a wide variety of phenomena pertaining to its operations which if not properly addressed and rectified may lead to catastrophic failure of the system. One such rotor-bearing phenomenon is the self-acting rotor vibrations induced by the hydrodynamic bearings and popularly known as oil-whirl and oil-whip which have severe repercussion on the functioning of the rotors. Another important area of rotor dynamics is the unbalance response of the rotors supported on the hydrodynamic journal bearings. Due to the inherent unbalance present in the rotor-bearing system high amplitude of vibrations are observed when the rotor is operated near its critical speed. In this context, a study of the rotorbearing system considering the non-linearity of the oil-film forces is necessary. In this thesis a methodology has been proposed to study stability and the unbalance response of a flexible rotor supported on two identical porous hydrodynamic journal bearing. Timoshenko Beam theory has been used for finite element formulation of the rotor. Finite hydrodynamic porous oil-film bearing is trajectories are shown. The stability curves have been drawn for different rotorbearing parameters. The effect of bearing location is also studied. Then unbalance is introduced in the model. Waterfall diagrams are obtained to study unbalance, oil-whirl for different rotor-bearing parameters. It has been observed that at low spin speed, unbalance is the major driving force and with an increase in the spin speed, oil-film forces take over as the major cause of vibration. Thus, whirling of the rotor gradually changes from synchronous to sub-synchronous. Waterfall diagrams are obtained for both run-up and run-down processes. Distinct dynamic behaviours are observed for run-up and run-down, which is known as hysteresis. Bifurcation analysis of the rotor-bearing system has also been carried out and PoincarD maps, time response, FFT-spectrum, dynamic trajectories and bifurcation diagrams have been utilized as diagnostic tools to study the non-linear dynamics of the rotor-bearing system. It has been found that the dynamic behaviour of the system can be periodic and quasi-periodic depending on the operating conditions. Also it is observed that when rotating speed is increased the rotor-bearing system undergoes Hopf Bifurcation. Initially, analysis of rotors supported on porous journal bearings have been carried out with an assumption that the lubricating fluid enters the clearance space of the bearing with a zero tangential velocity at the porous medium. However, earlier investigations suggest that this assumption is at best an approximation only. Therefore, the effect of tangential slip velocity using Beavers-Joseph criterion has also been carried out. Th....
Analysis of Three Phase Carbon/(CNT+Epoxy) Composites with Flaws
(2024) Rao, Chukka Atchuta
Three phase FRP composites like carbon/(CNT+epoxy) are developed where the matrix dominated properties of FRP composites are enhanced to improve the performance. FRP composites though possess a very high specific strength and stiffness sometimes show poor performance when their interlaminar strengths are challenged. Especially when defects like ply break and embedded delaminations occur due to events like low velocity impact, delaminations usually grows at the interface of the broken and intact plies leading to the final fracture. These defects are sub-surface in nature many a time go unnoticed and results in catastrophic failure. It is therefore extremely important to strengthen the laminates against such failure. Resistance against such failures are decided predominantly by matrix dominated properties like interlaminar strengths. Therefore, three phase composites such as carbon/(CNT+epoxy) with modified matrix properties is expected to provide improved resistance against such failure. The present thesis thus aimed at investigating the performance of three phase carbon/(CNT+epoxy) laminates having internal flaws like ply break and impact induced embedded delamination subjected to loading with the specific objective of understanding qualitatively and quantitatively how adding CNTs to the epoxy enhances the resistance delamination growing from such defects. To study this, full 3D finite element analyses (FEA) have been carried out for carbon/(CNT+epoxy) laminates having two types of flaws viz. ply break and embedded delamination. Delamination at the interface has been modelled using a very thin resin rich layer and the interlaminar stresses around the ply break and embedded delaminations are obtained from the 3D FEA. Using the stresses and displacements from FEA, Virtual Crack Closure Integral (VCCI) has been used to determine strain energy release rate (SERR) components as measures of propensity of delamination. FE results show that delamination from such defects is a mixed mode phenomenon and in the case of embedded delamination the mode mix ratio also varies along the delamination front making the estimation of delamination growth difficult. Delamination at the interface arising from such flaws are observed to be influenced by many factors such as size, shape, relative fiber orientation, loading condition. Critical SERR as a measure of resistance to such delamination has been evaluated in the present work using stress based criteria and virtual crack closure integral from LEFM. From the results, it is clear that in the case of three phase carbon/(CNT+epoxy), addition of CNTs to epoxy leads to significant improvement in resistance to delamination at the interface from ply bear as well as from embedded delamination in all the cases studied. In addition, it was also observed that tendency of two neighbouring delamination to grow as a large delamination is also reduced by adding CNTs to the epoxy. However, results from the FE simulations also show that there is a limit till which CNTs could be added to the epoxy for best performance and beyond this the performance further reduces and it is important to know the limit to the adding CNTs will enhance the resistance to such delamination.
Application of Cold Metal Transfer Technology for Cladding of ER70S-6 Alloy on AA 6061-T6 Aluminum Alloy
(2024) Das, Bappa
The Cold Metal Transfer (CMT) process is a specialized welding technique used for cladding and coating, which involves applying a layer of metal onto a base material. In fact, CMT cladding is an efficient additive manufacturing technology that finds application in the automotive, defence, and power plant sectors. As Additive Manufacturing evolves, new welding methods have emerged, including CMT, an advanced version of Metal Inert Gas (MIG) welding known for reduced spatter and low heat input. CMT-based cladding processes have gained attention for improved aesthetics and lower heat input. Utilizing a wire as feedstock and a robotic arm for deposition enables precise material placement in complex shapes, with heat input determined by process parameters like voltage, current, wire feed speed, and stand-off distance.
Application of electromagnetics in forming of tubes and perforation of sheets
(2017) Patel, Chandrahas
Electromagnetic forming (EMF) is a high strain rate forming process that utilizes high strength electromagnetic pressure to form tubes and sheets in the desired shape. High strain rate forming process successfully addresses the problems faced in conventional forming techniques such as springback, wrinkling and formability. It can be effectively used for forming metals with low formability like aluminium alloys. It can be instrumental in the manufacturing of lighter vehicles with higher fuel efficiency. In the present study, the emphasis is on the study of the electromagnetic forming of tubes and sheets with application to simultaneous electromagnetic forming and perforation of sheets.
Application of the Lattice boltzmann method in solving energy Equations of heat transfer problems involving thermal radiation
(2008) Mondal, Bittagopal
Abstract is not available
Assessment of feasibility, productivity and product quality during laser based bending of magnesium alloy sheets
(2016) Kant, Ravi
Magnesium alloys have low density, high specific strength, high stiffness, superior damping capacity, high thermal conductivity and good electromagnetic shielding characteristics. These properties make them suitable for a wide range of industrial applications. In present work, experimental and numerical studies were carried out to assess the feasibility, productivity and product quality during laser based bending of magnesium alloys. The experimental studies revealed that magnesium alloys can be bent with laser bending process without catching fire and significant deterioration in mechanical properties. Numerical model was developed by considering temperature and strain rate dependent material properties and the effect of melting. A model based on standard beam propagation equations was used to obtain beam diameter from stand-off distance. The straight line, curvilinear and multi-scan laser bending of magnesium alloy M1A sheets were investigated by using the developed numerical model. The effects of process parameters, viz. laser power, scan speed, beam diameter, scanning path curvature and number of scans on performance parameters such as temperature and stress-strain distribution, bend angle, edge displacement and edge effect were studied. It was observed that laser bending process parameters have a complex interactive non-linear effect on performance parameters. In curvilinear laser bending, it was observed that bending does not occur along the scanning path unlike in straight line laser bending. The results showed that bending was offset outside the scanning path. Laser bending does not generate large bend angles in a single scan and hence multi scan laser bending was studied. Large bend angles as high as 18º could be achieved in ten scans.The changes in bending mechanism, bend angle and edge effect with number of scans were explored during multi-scan laser bending process. A novel integrated, simple and efficient technique of laser assisted bending with moving pre-displacement load was proposed for bending of large sheets. The experimental setup was designed and developed to achieve the defined objectives. It was observed that the proposed technique was able to generate large bend angle in a single scan. The numerical model was developed and validated for the proposed technique. The validated model was used to investigate the effects of laser power, scan speed, beam diameter and pre-displacement on the bending mechanism, edge displacement, residual stresses, bend angle, edge effect and spring-back effect during laser assisted bending with moving pre-displacement. The present work contributed systematic and extensive numerical as well as experimental studies on laser bending of magnesium alloy M1A.

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