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Reduction in magnetic exchange bias in CoFe/FeMn/CoFe trilayers due to reduced pinned uncompensated moments in AFM layer
No full textThe M-H hysteresis curves of field cooled CoFe/FeMn bilayers and CoFe/FeMn/CoFe trilayers were studied to understand the exchange bias phenomena in these systems. The measured data revealed that the values of the exchange bias corresponding to a bottom CoFe layer reduced by about 23.5% with an addition of another CoFe layer at the top of bilayer stack. It was also observed that, while this reduction in exchange bias of a bottom CoFe layer (calculated in %) depends on thicknesses of a top CoFe layer and an antiferromagnetic FeMn layer, it is independent of the thickness of bottom CoFe layer. As the strength of exchange bias depends on the presence of pinned uncompensated moments in an antiferromagnetic layer, our observations indicate that the FeMn layer consists comparatively lower amount of pinned uncompensated moments in trilayers. This reduction in pinned uncompensated moments of FeMn layer in trilayers is then co-related with the domain wall suppression in the FeMn layer in CoFe/FeMn/CoFe trilayers
Vibration Analysis of Heterogeneous Gearbox Faults using EMD Features and SVM Classifier
Get PDFGearbox is one of the important mechanical power transmission device most
commonly used in automobiles and industries to get the desired change in speed and torque.
The gearbox fault diagnosis has given utmost importance for its significance in preventing
halts of a mechanical system and guaranteeing an advantage of sufficient maintenance. This
paper presents the vibration analysis of heterogeneous gearbox faults using EMD features and
SVM classifier. The vibration signal is converted into intrinsic mode functions (IMF) with
decreasing order of frequencies using empirical mode decomposition (EMD) method. Feature
vector consisting of information theoretic features have been computed for each IMF and
concatenated to form a feature set. By using random permutations, the feature set has been
divided into training and testing sets. The support vector machine (SVM) algorithm has been
used as a classification technique to diagnose the gearbox faults, which consists of five-class
classification. The accuracy of the developed algorithm has been validated using 100 Monte
Carlo runs. A comparative study has been carried between computed features and varying IMF
components. The observations made were - clear discrimination of the gearbox faults and
improved classification accuracy, which contain - chipped tooth, missing tooth, root fault,
surface fault and healthy working state of the gear
Microstructure and mechanical properties of Al – 3Mg – 0.25 Sc alloy sheets produced by cryorolling
No full textAl-3Mg-0.25Sc alloy with 50% and 75% rolling reductions from the initial thickness at room and cryogenic temperatures resulted in a higher dislocation density, enhanced lattice strain and reduced crystallite size for the cryorolled (CR) sample with 75% reduction (CR 75). A hierarchical grain size distribution was noted in CR samples through electron backscattered diffraction studies that led to a combination of 490 MPa of strength and 27% of ductility in CR 75. Also, due to hierarchical grain distribution, during the tensile test, deformation was expected to follow a complex strain distribution rather than localised necking, which had resulted in higher elongation. Further, a low mechanical anisotropy and a proportional decrement in texture index with a higher fraction of Cube texture enhanced the ductility of CR 75 among the rolled samples. Higher work hardening rate was reported by the CR samples than that of room temperature rolled (RTR) ones due to the influence of cryorolling and the existence of Al3Sc precipitates. Among the rolled samples, the CR 75 sample reported a higher necking percentage of 24% based on the stress based necking limit and fracture limit diagram, which indicated its ability to withstand higher strain before failure was consistent with the mechanical properties reported
Probabilistic evaluation and design aspects for reliability enhancement of induction motor
No full textThis paper presents the probabilistic evaluation, design aspects and scientific suggestions to improve the reliability and performance of an industrial induction motor. The induction motors have experienced a long life and a high efficiency in service with appropriate design and quality control. However, reliability quantification and adequacy evaluation are still necessary and important for customer satisfaction, design improvement, marketing, vendor selection, production plan, service life determination, and scheduled maintenance. The industrial data related to manufacturing and failure of induction motors are analysed for reliability assessment and design suggestions. The reliability indices like Mean Time Between Failure (MTBF) and failure rate of induction motors are evaluated using industrial data-based exponential probabilistic distribution function, which is issued to plan the maintenance schedule of the industrial induction motors. The technological suggestions are finally presented in this paper to reduce the failure rate and enhance the MTBF for reliability improvement of induction motors
Study of vortex breakdown and pitch up on a compound delta wing
Get PDFThis paper discusses the calculation of mean pressure on a compound delta wing configuration and its variance to understand vortex breakdown and pitch up on the setup. The configuration of the compound delta wing being used was 50°-60°. The data was used to find the location of vortex breakdown and pitch up over the compound delta wing. It was done using calibration of different pressure ports on span and chord wise location of the wing. The pressure values were then converted to Coefficient of Pressure (Cp) for proper study and comparison
Synthesis and characterization of high-performance epoxy/ Ti3AlC2-reinforced conductive polymer composites
No full textTitanium aluminium carbide powder was reaction synthesized and used as reinforcement in the aircraft grade epoxy matrix (LY556) to develop a high-performance conductive polymer composite. The particle sizes of 4 and 7 µm were employed from 0 to 40 wt.% to improve the mechanical and electrical properties of conductive polymer composites. It was observed that the percolation characteristics were exhibited at a critical threshold of 20 wt.% for both the filler particle sizes. Further, microstructural observations revealed the formation of a conductive network in the conductive polymer composites when the filler content was 20 wt.%. The tensile and flexural properties were increased when the particle size was decreased. Experimental values were then compared with the available analytical models for validation. The mechanical and electrical properties of the conductive polymer composites were optimized by tailoring the filler particle size to 4 µm and particle loading at 20 wt.%. Compared to neat epoxy, the optimized conductive polymer composites have shown a simultaneous increase in strength, stiffness and conductivity performances, which can find applications in aerospace and electronics industries
Thermally evaporated Cu–Al thin film coated flexible glass mirror for concentrated solar power applications
No full textThis paper reports the development of mechanically flexible reflective coatings of Cu–Al intermetallic alloy on flexible glass (FG) substrates for possible concentrated solar power application. Thin films of Cu–Al intermetallic alloys were deposited on 100 μm thick FG substrates using resistive thermal evaporation of arc melted Cu–Al bulk alloy. At the optimized evaporation conditions, smooth intermetallic alloy thin films with homogeneous composition (Cu0.78Al0.22) were obtained. At a coating thickness of 160 nm, average specular and total reflectance of ∼84% and ∼92% respectively, were achieved. The films exhibited hydrophobic nature with a contact angle of 102°, implying the possibility of developing a self-cleaning ability. The analytical calculation involving alloy compositional dependence of plasma frequency reveals the prospect of further modulating the reflectance property by carefully tailoring thin film composition. Additionally, hard intermetallic thin film provides the opportunity of developing mirrors that may not require top protective coatings
Improved hot corrosion resistance of plasma sprayed YSZ/Gd2Zr2O7 thermal barrier coating over single layer YSZ
Get PDFIn recent years, research is focused on the development of rare earth zirconates based thermal barrier coatings (TBC). In the present study, bilayered 8 wt% yttria stabilized zirconia (YSZ)/gadolinium zirconate (GZO) TBC system has been developed by atmospheric plasma spraying (APS) process from powders prepared by a single step co-precipitation technique. Hot corrosion behavior of all the coatings are tested in fused Na2SO4+ V2O5 mixture at the concentration of approximately 25 mg/cm2 at 910 °C for 30 h. Formation of gadolinium vanadate (GdVO4) is observed to be the corrosion product in YSZ/GZO bilayer coatings from Energy Dispersive X-ray analysis (EDAX) and is further confirmed by X-ray diffractometry (XRD) analysis. FESEM cross-section analysis of the YSZ/GZO bilayer coating after corrosion test affirms the effectiveness of the bilayer design in preventing the penetration of corrosive salts to the YSZ layer. Also, YSZ/GZO bilayer TBC exhibited a higher thermal cyclic life (300 cycles) than the single layer 8YSZ (175 cycles) coatings at 1100 °C
cartridge based Point-of-Care device for complete blood count
No full textWe demonstrate a proprietary lab-on-chip/μ TAS technology platform for a regulatory grade portable instrument for complete blood count (CBC) hematology tests including 3 part differential WBCs, RBCs, platelet and hemoglobin for rapid diagnostics at the point of care in resource-poor settings. Presently, diagnostics based on blood tests are confined to centralized laboratory settings, dependent on large footprint and expensive cytometers or on a microscope, requiring trained laboratory technicians. Consequently, such facilities are not present in rural and semi-urban settings, where there are opportunities and challenges in delivering efficient healthcare infrastructure at an affordable cost in resource-challenged environments. Our proposed design leverages advances in microfluidics and lab-on-chip fabrication techniques to miniaturize the conventional cytometer and bring down the cost significantly. The device can be operated autonomously, without skilled manpower, by primary healthcare professionals in the field and by patients (like glucose self-test devices). The instrument consists of a single-use chip, the size of a credit card, pre-loaded with reagents, in which the sample is loaded, and which is fluidically insulated from the environment. The controller, the size of a toaster, performs the necessary fluid handling and the impedance measurements to deliver the results in minutes
A comparative study of tensile strength of Cf/SiC composites having single layer and multilayer interphases
No full textTensile behaviour of stitched 2D carbon fiber reinforced silicon carbide (Cf/SiC) composites having variable interphases was studied in detail. Two types of interphases (single layer of pyrocarbon interphase and multilayers of pyrocarbon/silicon carbide) were deposited initially on the carbon fiber preforms followed by silicon carbide matrix infiltration. Multilayer interphase was deposited for two different durations. Cf/SiC composites were prepared by isothermal chemical vapour infiltration (ICVI) technique. The as-cut and silicon carbide seal coated samples were subjected to tensile tests in air at room temperature and at 1200 °C. The effect of seal coating and type of interphase on the tensile properties was studied. It was observed that the composites (in uncoated and seal coated condition) with multilayer interphase showed higher values of tensile strength at both the test temperatures as compared to single layer interphase. Also, the composites fabricated with multilayer interphase deposition for longer duration showed highest values of tensile strength at both the test temperatures. The fractured regions of tensile tested samples were analyzed in detail by SEM in order to understand microstructure-property relationships