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Cold-Sprayed Cu-Zn-Al2O3 Coating on Magnesium Alloy: Enhanced Microhardness and Corrosion Behavior
No full textThe present paper is aimed to improve the microhardness and corrosion protection of magnesium (AZ31B) alloy by employing Cu-Zn-Al2O3 coating through cold spray method. A fully dense coating of thickness ~ 877 μm has been achieved due to hammering effect of dense Al2O3 particles. The compositional and microstructural analysis of feedstock powder as well as coatings has been studied and discussed. An enhanced microhardness value of 219 ± 7 HV0.1 (~ 3 times higher) is obtained for Cu-Zn-Al2O3 coating compared to bare Mg alloy substrate (70 ± 10 HV0.1). The corrosion properties of the coatings were examined by potentiodynamic polarization and long-term immersion tests (24, 48, 96 and 336 h) in a 3.5% NaCl solution. Long-term immersed samples showed a positive shift in potential compared to the as-sprayed coated sample. The polarization resistance (Rp) measured is well in accordance with the measured Icorr. Coated samples after immersion for 336 h in 3.5% chloride medium resulted in the formation of a protective passive layer of ZnO and simonkolleite on the surface, which is responsible for corrosion protection of AZ31B alloy. These results are well supported by FESEM, EDAX and XRD data. This study provides an eco-friendly approach for corrosion protection of AZ31B alloy
Using eye tracking system for aircraft design – a flight simulator study
No full textThe authors of this paper investigated applications of eye tracking in transport aircraft design evaluations. Piloted simulations were conducted for a complete flight profile including take-off, cruise and landing flight scenario using the transport aircraft flight simulator at CSIR-National Aerospace Laboratories. Thirty-one simulation experiments were carried out with three pilots/engineers while recording the ocular parameters and the flight data. Simulations were repeated for high workload conditions like flying with degraded visibility and during stall. Pilot’s visual scan behaviour and workload levels were analysed using ocular parameters; while comparing with the statistical deviations from the desired flight path. Conditions for fatigue were also recreated through long duration simulations and signatures for the same from the ocular parameters were assessed. Results from the study found correlation between the statistical inferences obtained from the ocular parameters with those obtained from the flight path deviations. The authors of this paper investigated an evaluator’s console that assists the designers or evaluators for better understanding of pilot’s attentional resource allocation
Electrospinning of functional ceramic nanofibers
No full textNanofibers are one dimensional solid state structures with high aspect ratio and high surface area to volume ratio. The enhanced functional properties associated with nano structures of these nanofibers attracted the researchers to study and explore for various functional applications. Ceramic nanofibers are quite interesting for various functional applications such as gas sensors, capacitors/dielectrics, piezo-electrics, membranes for water and air filtration, microwave shielding, energy harvesting and storage, miniaturized electronic devices, as reaction catalyst etc. Among different processing techniques for preparation of ceramic nanofibers, electrospinning is relatively a new/modern straightforward technique which generates perfect ceramic nanofibers. In this review article, an overview of preparation and characterization of various ceramic nanofibers such as alumina, samaria, manganese tetroxide, tin oxide, barium titanate, barium calcium tin titanate (BCSnT) and their possible functional applications is presented
Mitigation of Antisymmetric Mode and Drag With Base Cavities
No full textExperiments were carried out to examine the impact of base cavities on the base pressure fluctuations and total drag of a cylindrical afterbody for freestream Mach numbers 0.6–1.5. Significant improvement in the base pressure and a substantial reduction in the afterbody drag was noticed in the presence of a base cavity at subsonic Mach numbers. However, on increasing the cavity length beyond a certain value, its performance deteriorates. At supersonic Mach numbers, their effectiveness drops drastically. Tones in the spectra can be classified into two types depending on the dominant azimuthal mode, which is either 0 or 1 and are referred to as symmetric and an antisymmetric mode, respectively. Spectra at subsonic Mach numbers exhibit tones, which are related either to mode 0 or 1. However, at supersonic Mach numbers, only tones related to mode 0 exist. The base cavity either effectively suppresses the antisymmetric mode or modifies it into a symmetric mode resulting in mitigation of the tones related to antisymmetric mode
Pyrolysis and thermal degradation studies of silane-carbosilane transformation using hyphenated thermal analysis
No full textPyrolysis process accompanying polydimethylsilane to polycarbosilane transformation and the decomposition behaviors of polydimethylsilane (PDMS), polycarbosilanes (PCS Mk-I/II and III) were investigated applying evolved gas analysis and pyrolysis–gas chromatography-mass spectrometry. Volatile fractions evolved during the reactions were recorded as specific pyrograms. The degradation of the polymer skeleton under argon leads to the evolution of methyl silane and higher linear oligomers in the molar mass range 42 ̶ 348 Da; the escape of hydrogen starts simultaneously. Based on the results, specific pyrolysis patterns and decomposition behavior of PDMS, PCS Mk-III were established. Mass spectral data revealed the structural and compositional identification of molecular moieties evolved during the pyrolysis reactions. Thermal data confirmed and complemented the pyrolysis data
A novel shape memory polymer composites with grafted hydroxyapatite nanoparticles for high strength and stiffness applications
No full textShape memory polymer (SMP) composites have evolved uniquely, employing nanoscale fillers, which add multifunctionality to the basic resin. In this work, the effect of inorganic, grafted hydroxyapatite (g-HAp) nanoparticles on the dynamic (mechanical), thermo-mechanical and microstructural properties of copolymer, based on diurethane dimethacrylate (DUDMA), (t-butyl acrylate (tBA), and crosslinker poly(ethylene glycol) dimethacrylate (PEGDMA), has been investigated. The agglomeration of nanofillers is limited by using PEG dimethacrylate monomer to graft HAp nanoparticles. Importantly, it is observed that mixing DUDMA in (tBA + PEGDMA) has improved the Young's Modulus of SMP composite to 5.4 GPa at RT (comparable to aircraft grade resin) with a glass transition temperature (Tg) of 55°C. Tensile stress is high as 51.46 MPa with improved strain at failure from 0.07% to 0.05%. The elongation strains of 4–8% are achieved, which provide the required strain compatibility to develop aerospace SMPs as well as SMP composites for structural and bio-medical applications
Multicriteria optimization of variable thickness plates using adaptive weighted sum method
No full textIn this paper, a multicriteria design framework for variable thickness isotropic plates using the
adaptive weighted sum method is developed. The design objectives are the minimization of weight and static
displacement and the design variables are the elemental thicknesses of plates modelled using finite elements.
Here, the multicriteria optimization framework is constructed by integrating the finite element method, ana-
lytical sensitivity technique along with optimization algorithms. The first-order shear deformation theory is used
in the static and dynamic analyses of plates. Both single and multiobjective optimization studies are conducted
to study the optimal thickness distributions of variable thickness plates under static and dynamic constraints. To
study multicriteria optimization of plates, the weighted sum method is first applied which gives sparsely
distributed Pareto optimal solutions. Then, the adaptive weighted sum method is employed where a coarser
representation of Pareto optimal solutions is generated using the weighted sum method and less populated
regions are identified for further refinement. The suboptimization problems are solved in these regions to
determine a new set of Pareto optimal solutions. The Pareto optimal curves obtained using the adaptive weighted
sum method are also compared with the conventional weighted sum method under different constraints. The
effect of boundary conditions on the Pareto optimal solutions and thickness distributions of plates is also
investigated
High Strain Rate Behavior of GTM-900 Titanium Alloy
No full textGTM-900 is an α + β alloy of titanium used in low-pressure (LP) compressor blades of gas turbine (GT) engines. The maximum allowable operating temperature of this alloy is 500°C. Silicon is added to enhance the creep resistance at elevated temperatures. The aim of this work is to establish the microstructural stability of this alloy and determine the high strain rate Johnson-Cook (J-C) material parameters such as A, B, and n. The material parameters are subsequently used by designers to simulate the “blade-off” and “casing containment” capability of the LP compressor blade. Split Hopkinson tensile bar was used to conduct high strain rate tests at about 2,000 s−1, and at three different temperatures, viz., 25°C, 300°C, and 500°C, to simulate critical conditions. Data obtained from these testing were used to construct a J-C model. Flow stress increased with an increase in strain rate and decreased with an increase in temperature because of thermal softening. Characterization, using optical and electron microscopes, indicated that the microstructure was stable even after the deformation at 500°C. The presence of needle-like silicide phase was observed under transmission electron microscopy and the composition was verified with X-ray diffraction results. A high strain hardening rate was observed even at elevated temperatures in this alloy (n ≈ 0.54 at 2,000 s−1 and 500°C) compared to Ti-6Al-4V titanium alloy (n ≈ 0.28). Considering good strength and microstructural stability up to 500°C, the present material offers to be an attractive alternate to other contemporary titanium alloys currently used in GT engine applications
Covid-19 Pandemic: Need to Exercise Caution While Using Hypochlorite Sanitizer in Manufacturing Industries
No full textWorld is fighting Covid-19 pandemic since beginning of the year 2020. To prevent spread of Covid-19 disease, sanitization of workplaces using sodium hypochlorite (NaOCl) disinfectant is one of the several precautionary steps that are followed currently. In this letter, I share an experience wherein regular spraying of NaOCl solution in metal forming section of an organization led to development of corrosion damage and rejection of a large number of aircraft structural components made of Al-2024 alloy sheet material
Validation of Numerical Analysis Results for Pusher Configured Turboprop Engine Air Intake
No full textIn the course of an aircraft development program of LTA, a number of engine-related ground and flight tests have to be carried out to determine the losses particular to the engine installation. These installation losses must be determined in order to create the final aircraft power setting charts. During the course of configuration development, design analysis is a must to ensure that the proposed design will perform the intended operation within the estimated losses, this confidence should be assessed either in a bench tests or in CFD analysis. The numerical study of engine air intake performance is carried out using RANS-based k- ω SST using ANSYS FLUENT software. The study is carried out for minimum climb condition, as it is critical operation of any aircraft mission. The CFD results were compared with the flight test data for validation. The instrumentation that is necessary to measure installation losses and engine performance has been installed. Computational results agree well with the experimental results and were found satisfactory. The CFD results of air intake show that the total pressure is extensively recovered at the engine intake plenum (compressor inlet screen) region, and the inlet pressure loss and ram air recovery were within the acceptable limit as recommended by engine OEM