Showing papers by "National Aerospace Laboratories published in 2018"

Novel Metamaterial-Element-Based FSS for Airborne Radome Applications

Abstract: A novel metamaterial (MTM) element for radome applications is presented in this paper, which shows negative permittivity and permeability characteristics at distinct frequency ranges. The MTM element is composed of tightly coupled Swastika-shaped conductors printed on both sides of the dielectric substrate. The electromagnetic (EM) analysis of the proposed structure is carried out using the full-wave method-based standard software package and then validated with the experimental results. The MTM structure is further modified by introducing shorting strips at its edges to improve bandpass FSS response with flat-top and sharp roll-off characteristics in microwave and millimeter-wave frequency regimes. In view of airborne radome application of MTM-FSS structure, a multilayered hemispherical radome is designed by embedding it in the mid-plane of the radome wall. The EM performance of the antenna–radome system is analyzed using 3-D ray tracing geometrical optics in conjunction with aperture integration method, incorporating the transmission characteristics of MTM-FSS-based radome wall using CST Microwave Studio. The MTM-FSS-based radome exhibits superior EM performance characteristics as compared to the conventional optimized monolithic radome over the frequency range of 8.5–10.3 GHz, with high transmission efficiency (~0.30) and minimal boresight error (~4 mrad) for the entire beam steering range.

Tailored periodic Si nanopillar based architectures as highly sensitive universal SERS biosensing platform

Abstract: We report a skeleton key platform for surface enhanced Raman spectroscopy (SERS) based biosensor, utilizing ordered arrays of Si nanopillars (SiNPLs) with plasmonic silver nanoparticles (AgNPs). The optimized SiNPLs based SERS (SiNPLs-SERS) sensor exhibited high enhancement factor (EF) of 2.4 × 108 for thiophenol with sensitivity down to 10−13 M of R6G molecules. The ordered array of SiNPLs stabilizes the distribution of AgNPs along with the light trapping properties, which resulted in high EF and excellent reproducibility. The uniformity in the arrangement of AgNPs makes a single SiNPLs-SERS substrate to work for all types of biomolecules such as positively and negatively charged proteins, hydrophobic proteins, cells and dyes, etc. The experiments conducted on differently charged proteins, amyloid beta (the protein responsible for alzheimers), E. coli cells, healthy and malaria infected RBCs provide a proof of concept for employing universal SiNPLs-SERS substrate for trace biomolecule detection. The FDTD simulations substantiate the superior performance of the sensor achieved by the tremendous increase in the hotspot distribution compared to the bare Si sensor.

In Vitro Corrosion Behaviour of Ti–6Al–4V and 316L Stainless Steel Alloys for Biomedical Implant Applications

Abstract: Pulsed laser deposition technique is one of the methods to coat the hydroxyapatite on 316L stainless steel and Ti–6Al–4V implants, which is used in orthopaedics and dentistry applications. In this study, hydroxyapatite (HAP) ceramics in the form of calcium phosphate were deposited on Ti–6Al–4V and 316L stainless steel by the pulsed laser deposition method. The coated thin film was characterised by X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (EDS) and atomic microscopy. The corrosion studies were carried out on coated and uncoated samples using potentiodynamic polarisation studies in simulated body fluid (Hanks’ solution). The bioactivity of the Hap-coated samples on Ti–6Al–4V and 316L stainless steel was evaluated by immersing them in simulated body fluid for 9 days. XRD and EDS analyses confirmed the presence of HAP. The corrosion studies showed that the treated samples have better corrosion resistance compared to Ti–6Al–4V and 316L stainless-steel substrates. The formation of apatite on treated samples revealed the bioactivity of the HAP-coated substrates. HAP-coated Ti–6Al–4V provides higher corrosion protection than the HAP-coated 316L stainless-steel substrates.

Highly sensitive giant magnetoresistance (GMR) based ultra low differential pressure sensor

Abstract: In this study, we demonstrate a simple, cost-effective, giant magnetoresistance (GMR) based magnetic pressure sensor The basic principle lies behind the measurement of the change in the magnetic field profile generated by the deflected diaphragm attached with a permanent magnet This magnetic field profile change on the sensor surface was measured by highly sensitive magnetoresistive gradiometer sensor Based on studied magnetic field distribution of a magnet, a prototype pressure sensor was designed and fabricated, which consists of a polymer diaphragm, a permanent magnet and a giant magnetoresistance based magnetic field gradient sensor The fabricated prototype was calibrated for ultra-low differential pressure range and it shows: (i) sensitivity up to 1667 μV/V/Pa and (ii) nonlinearity of 15% FS in the range of 0–300 Pa The real time application was demonstrated where, the sensor was flush mounted on a NACA 4415 airfoil, and both the static and the dynamic suction pressures were recorded as a function of the wind velocity and also with different angle of attack (AOA) The measured pressure was found to be highly accurate while compared with existing static measurement system

Enhanced mechanical properties of acrylate based shape memory polymer using grafted hydroxyapatite

Abstract: In the present study, the effect of grafted and ungrafted hydroxyapatite (HAp) filler on the mechanical properties of acrylate based shape memory polymer (SMP) composite is reported. HAp is grafted with polyethylene glycol methacrylate (PEGMA) monomer to avoid agglomeration and the same is embedded as reinforcement in tBA – PEGDMA matrix (70 wt% tBA: tert-butyl acrylate +30 wt% PEGDMA: polyethylene glycol dimethacrylate). The grafting process improved the interfacial interactions of the particles, dispersed in the polymer system and subsequently enhanced the mechanical properties of the shape memory polymer composites. The morphology of HAp particles is investigated by field emission scanning electron microscopy. The mechanical properties of SMP composites are evaluated at room temperature and above glass transition temperature (Tg) with grafted and ungrafted HAp particles. The addition of grafted HAp significantly improved the tensile strength (40%) and shape recovery rate (25%) of the SMP composite when compared to the SMP composite containing ungrafted HAp. SMP composite containing grafted HAp exhibited higher cell viability compared to the neat SMP and the SMP composite containing ungrafted HAp.

Corrosion and wear resistance properties of multilayered diamond‐like carbon nanocomposite coating

Abstract: Multilayered diamond‐like carbon (DLC) nanocomposite coating has been deposited on silicon and stainless steel substrates by combination of cathodic arc evaporation and magnetron sputtering. In order to make DLC coating adhered to metal substrate, a chromium interlayer has been deposited with constant bias voltage of −150 V applied to the substrate. Dense multilayered coating consists of metallic or nonmetallic and tetrahedral carbon (ta‐C) layers with total thickness of 1.44 μm. The coating has been studied for composition, morphology, surface nature, nanohardness, corrosion resistance, and tribological properties. The composition of the coating has been estimated by energy‐dispersive spectroscopy. Field‐emission scanning electron microscopy and atomic force microscopy have been used to study the surface morphology and topography. ID/IG ratio of ta‐C:N layer obtained from Raman spectroscopy is 1.2, indicating the disorder in the layer. X‐ray photoelectron spectroscopy studies of individual ta‐C:N, CrN, and Cr‐doped DLC layers confirm the presence of sp2C, sp3C, CrN, Cr2N, and carbidic carbon, and sp2C, sp3C, and Cr carbide. Nanohardness studies show the maximum penetration depth of 70 to 85 nm. Average nanohardness of the multilayered DLC coating is found to be 35 ± 2.8 GPa, and Young's modulus is 270 GPa. The coating demonstrates superior corrosion resistance with better passivation behavior in 3.5% NaCl solution, and corrosion potential is observed to move towards nobler (more positive) values. A low coefficient of friction (0.11) at different loads is observed from reciprocating wear studies. Wear volume is lower at all loads on the multilayered DLC nanocomposite coating compared to the substrate.

Effect of Retrogression Heat Treatment Time on Microstructure and Mechanical Properties of AA7010

Abstract: The effect of retrogression time during retrogression and re-aging (RRA) treatment of AA7010 is evaluated by performing tensile tests and characterizing the microchemistry of the grain boundary precipitates (GBPs) using transmission electron microscope coupled with the energy-dispersive spectroscopy. Retrogression time is evaluated so that the ultimate tensile strength of the RRA-treated sample is equal to that of the T6-treated sample and the grain boundary microstructure similar to that of the over-aged (T7451) condition. The investigation reveals that the sample retrogressed at 200 °C for 20 min has UTS of 586 MPa which is equivalent to that of the T6 sample and 11.5% higher than that of the T7451 condition. The fracture toughness of the RRA-treated sample was 41 MPa√m. Microstructure of the RRA-treated sample is similar to T7451, along the grain boundaries and in the grain interior similar to that of the T6-treated sample. Energy-dispersive spectroscopy confirmed the increment of Cu content on the GBP’s with increase in the retrogression time, which is expected to improve the stress corrosion cracking resistance of the alloy.

Effect of multiwalled carbon nanotube alignment on the tensile fatigue behavior of nanocomposites

Abstract: The one-dimensional structure of carbon nanotubes makes them highly anisotropic, making them to possess unusual mechanical properties, and hence employed as promising nanofiller for the composite structures. However, various carbon nanotube properties are not completely utilized when they are used as reinforcement in composites due to inadequate and immature processing techniques. In the present work, an attempt has been made to utilize the strong anisotropic nature of multi-walled carbon nanotubes (MWCNTs) for improving the fatigue life of nanocomposites only by considering a very low weight percentage (<0.5 wt%). The anisotropy of MWCNTs was imparted into the nanocomposites by aligning them in the epoxy matrix with DC electric field during composite curing. Nanocomposites were made for three MWCNT loadings (0.1, 0.2, and 0.3 wt%). The tensile fatigue behavior was investigated under stress control by applying cyclic sinusoidal load with the frequency range of 1–3 Hz and stress ratio, R = 0.1. The specime...

Processing and characterization of lead-free ceramics on the base of sodium–potassium niobate

Abstract: Lead-free sodium–potassium niobate-based piezoelectric materials are most intensively studied in order to replace the widely used Pb-based ones. In this work, the effects of modification of composi...

Flexural Properties of PLA Components Under Various Test Condition Manufactured by 3D Printer

Abstract: Rapid Prototyping (RP) technologies have emerged as a fabrication method to obtain engineering components in the resent past. Desktop 3D printing, also referred as an additive layer manufacturing technology is a powerful method of RP technique that can fabricate 3 dimensional engineering components. In this method, 3D digital data is converted into real product. In the present investigation, Polylactic Acid (PLA) was considered as a starting material. Flexural strength of PLA material was evaluated using 3-point bend test, as per ASTM D790 standard. Specimens with flat (0°) and vertical (90°) orientation were considered. Moreover, layer thicknesses of 0.2, 0.25, and 0.3 mm were considered. To fabricate these specimens, printing speed of 38 and 52 mm/s was maintained. Nozzle diameter of 0.4 mm with 40 % of infill density were used. Based on the experimental results, it was observed that 0° orientation, 38 mm/s printing speed, and 0.2 mm layer thickness resulted maximum flexural strength, as compared to all other specimens. The improved flexural strength was due to the lower layer thickness (0.2 mm) specimens, as compared with other specimens made of 0.25 and 0.30 mm layer thicknesses. It was concluded that flexural strength properties were greatly influenced by lower the layer thickness, printing speed, and orientation.

Control of Incident Shock-Induced Separation Using Vane-Type Vortex-Generating Devices

Abstract: An experimental investigation was conducted to control an incident shock-induced boundary-layer separation associated with a 14 deg shock generator in a Mach 2.05 flow. Two vane-type configurations...

Mixed mode cohesive zone modelling and analysis of adhesively bonded composite T-joint under pull-out load

Abstract: The failure behaviour of three different configurations of adhesively bonded carbon fibre composite T-joints subjected to pull-out load is investigated. Finite element analysis is carried out on the carbon fibre composite T-joint models. A non-linear, contact target-based cohesive zone model with appropriate traction separation law is selected to simulate the pull-out test condition in FE package ANSYS®. The FE analysis results are in close agreement with available experimental results.

Experimental analysis and evaluation of a vacuum enclosed concentrated solar thermoelectric generator coupled with a spectrally selective absorber coating

Abstract: Significant research in the past decade has been focused on quantitatively and qualitatively validating potential of solar thermoelectric modules to harness electricity. In the present stud...

Electrochemical Behavior of Biomedical Titanium Alloys Coated with Diamond Carbon in Hanks’ Solution

Abstract: Biomedical implants in the knee and hip are frequent failures because of corrosion and stress on the joints. To solve this important problem, metal implants can be coated with diamond carbon, and this coating plays a critical role in providing an increased resistance to implants toward corrosion. In this study, we have employed diamond carbon coating over Ti-6Al-4V and Ti-13Nb-13Zr alloys using hot filament chemical vapor deposition method which is well-established coating process that significantly improves the resistance toward corrosion, wears and hardness. The diamond carbon-coated Ti-13Nb-13Zr alloy showed an increased microhardness in the range of 850 HV. Electrochemical impedance spectroscopy and polarization studies in SBF solution (simulated body fluid solution) were carried out to understand the in vitro behavior of uncoated as well as coated titanium alloys. The experimental results showed that the corrosion resistance of Ti-13Nb-13Zr alloy is relatively higher when compared with diamond carbon-coated Ti-6Al-4V alloys due to the presence of β phase in the Ti-13Nb-13Zr alloy. Electrochemical impedance results showed that the diamond carbon-coated alloys behave as an ideal capacitor in the body fluid solution. Moreover, the stability in mechanical properties during the corrosion process was maintained for diamond carbon-coated titanium alloys.

Biocompatible response of hydroxyapatite coated on near-β titanium alloys by E-beam evaporation method

Abstract: Biomedical implants such as dental and orthopedic implants fails due to poor mechanical and biological properties. In order to solve this problem, Electron beam (e-beam) evaporations is used as one of the methods to deposit the hydroxyapatite (HA) on Ti-13Nb-13Zr (near β titanium alloy) and the coated implant may play a significant role in increasing the mechanical and biological properties. In the present study, Ti-13Nb-13Zr was coated with hydroxyapatite (HA) by e-beam evaporation technique. The coated alloys were morphologically analyzed by FESEM and AFM, and it demonstrates that there is an increase in the growth of calcium phosphate layer. In-vitro corrosion behavior of the coated and uncoated titanium alloys were performed by electrochemical impedance spectroscopy (EIS) studies in simulated body fluid solution. The results show that the corrosion resistance of the hydroxyapatite-coated alloy higher than that of the uncoated alloys and it evident that the HA-coated alloy have better corrosion protection for the implant application. The bioactivity of the HA-coated composites were evaluated by Hanks’ solution immersed them for seven days. The ratio Ca/P was increased gradually after soaking it for seven days. The cell viability results indicates that HA coated alloys support increase in the Osseo integration and it can be used for bone implant application.