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MgO based specular spin valve with reversible minor loop and higher exchange bias for futuristic linear magnetic field sensor
No full textSpecular spin valves (SVs) containing ultrathin MgO, structured as substrate/seed/AF/PL1/MgO/PL2/Cu/FL/MgO/cap, have been fabricated. Both structural and magnetic characterizations of MgO based specular spin valve (SSV) have been performed and compared them with the measured data on naturally oxidized (NO) and conventional spin valves (CSV), grown under optimised condition. Reversible minor loop characteristics, highest exchange bias of 625 G and 10% magnetoresistive (MR) ratio were important observations in MgO based system. Zero hysteresis behavior was confirmed due to the reduction of grain growth of the stacks above the fine-textured MgO layer, through X-ray diffraction measurements. Interestingly, at 10 K, above 100% enhancement in MR ratio was observed in MgO based system with marginal increase in coercivity of the order 1 G. On the other hand, NO based structure has 10% MR, minor loop hysteresis of 2 G and exchange bias of 560 G at room temperature; however at 10 K, only 75% enhancement in MR ratio with large anomalies in magnetic measurements attributes due to the AFM nature of oxide materials. The above studies reflects the superior performance of MgO based SSV over a wide range of temperature in comparison to other SV structures and may lead to futuristic linear magnetic field sensor applications
Mach Number Effect on Symmetric and Antisymmetric Modes of Base Pressure Fluctuations
No full textAn experimental study aimed at evaluating the influence of Mach number on the base pressure fluctuations of a cylindrical afterbody was performed over a wide range of Mach numbers from subsonic to supersonic speeds. Time-averaged results indicate that the coefficient of base pressure drops with the increase in the freestream Mach number at subsonic speeds and increases at supersonic Mach numbers. The coefficient of root-mean-square of the pressure fluctuations follows a decreasing trend with the increase in the Mach number. Examination of the spectra reveals different mechanisms dominate the pressure fluctuations from the center to the periphery of the base as well as with the change in the Mach number. Analysis of the azimuthal coherence indicates that all the dominant tones in the spectra can be classified either into a symmetric or an antisymmetric mode at subsonic Mach numbers. However, at supersonic Mach numbers, all the dominant tones in the spectra are symmetric in nature. The results from the cross-correlation suggest that two possible mechanisms of recirculation bubble pulsing and convective motions/vortex shedding are driving the dynamics on the base at subsonic Mach numbers. However, at supersonic Mach numbers, only single mechanism of the recirculation bubble pulsing dominates. Moreover, it indicates that
the symmetric mode is associated with the dynamics of the recirculation bubble and the antisymmetric mode is related to the convective motions/vortex shedding
Nanolayered multilayer Ti/TiN coatings: Role of bi-layer thickness and annealing on solid particle erosion behaviour at elevated temperature
No full textSolid particle erosion is a very serious and inevitable issue faced by key components of modern machinery in various applications such as compressor blades and vanes of turbine engines, and turbine blades of advanced aircraft engines. In this direction third generation Ti/TiN nanolayered multilayered erosion resistant coatings were developed using sputtering technique. Films of around 7–10 μm total thickness with bi-layer thicknesses from 7.5–115 nm were deposited. Structural and mechanical properties such as hardness, toughness and stress of the films were studied, and correlated with the bi-layer thickness and deposition conditions. Erosion test was carried out according to ASTM G76-13 standard parameters at 30, 45, 60, and 90° impinging angles. Since the compressor blades of the gas turbine engines usually operate at 100 to 550 °C, the erosion tests were conducted at 400 °C. Films with lower bi-layer thickness showed better erosion resistance in comparison with higher bi-layer thickness films. Further, effect of bi-layer thickness, annealing and internal stress of the films on erosion resistance performance is studied. Detailed studies revealed that the optimized coating exhibited an improvement in the erosion performance by a factor of 15 compared to Ti6Al4V substrate
Estimation of failure load of composite bonded joints using 1D and 2D FE analysis and the mathematical equation of strain and bond energy in the adhesive layer
No full textAdhesively bonded composite (ABC) joints used in the composite structures are modeled using 1D and 2D elements to generate the finite-element mesh. The present modeling technique has captured the overall structural behavior of ABC joints precisely. The analytical study proposed a novel failure criterion of ABC joints after understanding the structural behavior of joints through the modeling approach. A failure criterion developed based on the principle of conservation of energy stored within the adhesive layer by virtue of its allowable strength properties and consumed by applying stress per a unit load. The ultimate failure load of joints of popular configurations is estimated based on the principle of conservation of energy. The 1D–2D finite-element modeling approach has revealed the presence of a new form of mechanical energy named as the Bond energy concealed within the adhesive layer. A new failure mechanism and their modes are explained through the novel failure criterion. The numerical value of Bond energy is calculated by using a peculiar mathematical relationship between the allowable shear strength property and the Young’s modulus of the adhesive layer. The ultimate failure load estimated by the novel failure criterion is compared with that of third-party experimental results and found fair agreement of 1–11% difference, which is acceptable with appreciation
Wind energy conversion in India
No full textThe cost of energy derived from manual labour in tasks like lifting water from wells and canals is estimated to be about 20 times higher than the commercial price for electricity. It appears that practically no serious attempt was made to utilize wind energy in India until the 1950s. While wind power has been utilized in propelling and guiding ships and boats, for several reasons no other utilization of wind energy could develop. One reason probably was the ready availability of animate energy derived from the muscle power of draft animals. The most common method of using wind energy is by conversion into shaft work. Electricity may be derived from shaft work simply by coupling a suitable generator to the windmill shaft. Wind-energy conversion into electricity through shaft work could be examined on the basis of the mode of utilization of electricity in Indian village
System identification
No full textSystem identification is a process of developing mathematical models for the dynamic system of interest, which can be used for the modelling and simulation, prediction, control design, error detection, etc. The process involves the various experimental procedures carried out for variable input signals, followed by the identification of mathematical model that best fits the system of interest. The accuracy of the selected mathematical model is then validated using System Identification Toolbox/MATLAB. The model with the best fit can be used for the further analysis of the system
Influence of retrogression and re-ageing heat treatment on the fatigue crack growth behavior of 7010 aluminum alloy
No full textAluminum alloys are widely used in aircraft structural components where light weight, high strength and good corrosion resistance are the primary requirements. These alloys are generally used in peak-aged (T6) condition in which they are susceptible for stress corrosion cracking. In the recent years, retrogression and re-ageing (RRA) treatment on aluminum alloy is carried out to enhance their corrosion resistance maintaining the ultimate tensile strength. The aim of this work was to study the influence of RRA treatment on the fatigue crack growth rate
(FCGR) behavior. The 7010 aluminum alloy was heat treated to two different conditions i.e., T6 and
RRA. The microstructures of these alloys were characterized by using TEM. Standard compact tension (CT) specimens were prepared and FCGR tests were carried out by using a 100 kN servo-hydraulic test machine as per ASTM E647-15e1. The constant amplitude FCGR tests were carried out at a stress ratio, R = 0.5 using sine wave loading pattern at 10 Hz. Crack length was monitored by following compliance technique. Microstructural studies show that RRA treated alloy contain fine and densely populated precipitates in the matrix along with coarse and discontinuous precipitates in the grain boundary. The fatigue crack growth rate was observed to reduce along with an increase in the threshold stress intensity factor range (ΔKth) for RRA treated alloy compared to the T6 alloy. The mechanisms for reduction in fatigue crack growth rate of RRA treated alloy is attributed to the microstructural modifications. The increased resistance is expected to enhance the damage tolerance capability of the alloy
A study on adsorption of gases in the thin film nanocomposites
No full textSeparation of greenhouse gases through polymeric thin film by the selective transport of gas are immense advantages such as light weight, economical, high process flexibility and less space requirement. The thin film technology is used in post combustion process as well as pre combustion processes. This thin film mixed matrix composites (MMC) is prepared using inorganic nanofiller and polymer matrix. In this study, the effect of Lanthanum Oxide (La2O3) nanofiller on the N2 gas adsorption properties of polysulfone (PSf) composite is reported. The solvent evaporation technique is used for synthesizing the film composite. To complete the polymerization of the thin film, the film kept in oven at 90°C for 210 minutes. The morphology of the thin film composite is investigated by Field Emission Scanning Electron Microscope (FESEM) and the chemical structure of the composite is also confirmed through Fourier transform infrared spectroscopy (FT-IR). The performances of the thin film on adsorption are characterized by gas adsorption techniques in measurement of N2 gas. The La2O3 thin film composite significantly improved (31%) N2 gas adsorption when compared to the neat thin fil
Analytical model of progression of flank wear land width in drilling
No full textIn multipoint operations like drilling, cutting velocities and cutting-edge geometries vary along cutting lips so is the rate of progression of flank wear. Analytical evaluation of flank wear land width in the case of complex tools has received a limited attention so far. This work evaluates progression of flank wear in orthogonal machining and adopts it to drilling. An abrasive flank wear has been modeled, wherein, cutting speed determines the rate of abrasion, and the feed rate determines the chip load. The model considers stress distribution along rake surfaces, and temperature-dependent properties of tool and work materials. Assuming that the flank wear follows a typical wear progression as in a pinon-disk test, the model evaluates cutting forces and the consequent abrasive wear rate for an orthogonal cutting. To adopt it to drilling, variation in cutting velocity and dynamic variation in rake, shear, and friction angles along the length of the cutting lips have been considered. Knowing the wear rate, the length of the worn-out flank (vb) has been evaluated. The model captures progression of flank wear in zones (i), (ii), and (iii) of a typical tool-life plot. It marginally underestimates the wear in the rapid wear region and marginally overestimates it in the steady-state region
Investigation on the mechanical properties of PLA & its composite fabricated through advanced fusion plastic modelling
No full textAdvanced Fusion plastic modelling (AFPM) based rapid prototyping (RP) technique was emerged as one of the potential Technologies for serving numerous three-dimensional product for tool design purposes. Primarily, Poly Lactic Acid (PLA) and Acrylonitrile Butadiene Styrene (ABS) are the key materials used for RP purposes. However, a PLA based composite was developed for RP applications. In this paper, an effort was made to prepare a PLA composite using bronze and cellulose as an additive. The objective of the proposed PLA composites is to performe the mechanical properties such as tensile and flexural strength at varied AFPM parameters like nozzle diameter, layer thicknesses and printing speeds. Three PLA composites including natural PLA and PLA with cellulose and bronze additives was prepared. Here, efforts were made on optimised the mechanical properties with the different composites and printing. The tensile and flexural strength of the PLA and its composites samples have been examined and with the nozzle diameter of 0.4 mm, layer thickness of 0.2 mm and the printing speed of 30 mm/s exhibited natural PLA has better tensile and flexural strength properties. The results also confirmed that the addition of bronze and Cellulose as additive exhibits moderate strength mechanical than the natural PLA but it has a pourous nature because of the gas produced in the printing process