National Aerospace Laboratories
National Aerospace Laboratories Institutional RepositoryNot a member yet
7121 research outputs found
Sort by
Exprimentation for flexural strength and fracture toughness on carbon and galss fiber self healing composites with bisphenol a diglycidyl ether and amine microcapsules
No full textThe present study investigates self-healing ability of carbon/E-glass fibers composites based on microcapsule approach under flexural and fracture loading. The proposed self-healing fiber reinforced composite constitutes epoxy resin (Lapox ARL-136+AH-126), unidirectional carbon, and E-glass fibers with different orientations such as 0°, 45°, and 90°, microcapsules of BADGE (monomer) and amine with AH-319 hardener as curing agent are embedded. The self-healing ability of the developed composites at different healing time (5, 6, and 7 days) and comparison of recovered flexural strength for carbon/E-glass fiber along different orientations are studied. On day 7 the healing efficiencies obtained are 61.89, 61.20, 78.30% and 64.50, 68.55, 82.77% for carbon/E-glass fiber orientation along 0°, 45°, 90° composite, respectively. By knowing the drawbacks of microcapsule-based system and to reduce the healing time, experimentally fracture properties in mode I, II, mixed-mode conditions, and efficiencies based on extrinsic approach are evaluated. Optimum healing efficiencies obtained in mode I for carbon/E-glass fiber orientation along 45° are 103.51 and 84.16%, respectively. Similarly in mode II for carbon fiber along 0° and E-glass fiber along 45°, obtained efficiencies are 130.32 and 84.48%, respectively. And, in mixed mode for carbon fiber along 90° and E-glass fiber along 45° obtained efficiencies are 232.78 and 119.23%, respectively. Optimum fracture toughness of healed is 75% as compared to virgin samples. The results show that the self-healing composites may provide excellent mechanical and fracture properties towards a wide range of structural applications
Preliminary aerodynamic design of A S-co2 axial turbine
No full textAxial turbines are gaining prominence in supercritical carbon-di-oxide (S-CO2) Brayton cycle power blocks. S-CO2 Brayton cycle power systems designed for 10 MW and upwards will need axial turbines for efficient energy conversion and compact construction. The real gas behavior of S-CO2 and its rapid property variations with temperature presents a strong challenge for turbomachinery design. Applying gas and steam turbine philosophies directly to S-CO2 turbine could lead to erroneous designs. Very little information is available in the open literature on the design of S-CO2 axial turbines. In this paper, design of a 10 MW axial turbine for a simple recuperated Brayton cycle waste heat recovery system is presented. Three repeating stages with nominal stage loading coefficient of 2.3 and flow coefficient of 0.37 were designed. An axial turbine mean-line design method tuned to S-CO2 real gas fluid medium is discussed. 3D blade design was made suing commercial turbomachinery design software AxSTREAM. The turbine was designed for inlet temperature of 818.15 K, pressure ratio of 2.2, rotational speed of 12000 rpm and mass flow rate of 104.5 kg/s. 3D CFD simulations were carried out using the commercial RANS solver ANSYS CFX 2020 R2 with SST turbulence model for closure. S-CO2 was modelled as real gas with Refrigerant Gas Property tables generated over the appropriate pressure and temperature ranges using NIST Refprop database. CFD studies were carried out over a range of mass flow rates and speeds, covering the design and several off-design conditions. The performance maps generated using 3D CFD simulations of the turbine are presented. The geometrical parameters obtained with the mean-line design matched well with that of the 3D turbine design arrived using AxSTREAM. It was observed that the turbine produced 10 MW power at the design condition while passing the required mass flow. CFD studies also showed that the preliminary turbine design achieved a moderate total-tototal efficiency of 80 % at the design condition. The design has potential for further optimization to obtain improved efficiency and for reducing the number of stages from three to two
Damage detection in composite aircraft wing-like test-box using distributed fiber optic sensors.
No full textStructural Health Monitoring Systems for the aircraft structures are intended to detect the location and size of the damage with minimum downtime of the aircraft. As the damage produces localized strain changes, a sensor network of many sensors bonded/embedded throughout the structure is required for damage diagnosis. This paper describes a distributed fiber optic sensor's demonstration to detect the disbond damage in a typical aircraft wing-like structure where a single optical fiber can cover a large area. Distributed fiber optic sensor is being bonded along the bolt line of the test-box. Controlled disbond are created by the removal of the bolts. In the pristine state, the strain signature/map is measured under applied load, which act as a reference in this case. In this approach, localized strain signature difference between the reference and disbond-structure is used to detect the damage. A non-dimensional quantity damage index (DI) is calculated based on the normalized sum of the square magnitude of strain difference of all sensors to indicate the damage severity. We have found that the DI value greater than or equal to 0.2 indicates the damage region through the iterative approach. Further, the algorithm is validated by loading the structure with disbond at different load levels. The maximum error in the disbond estimation is found to be ∼11 mm. This system and methodology hold immense promise for a ground-based method for detecting damage (disbond) in the aircraft/unmanned aerial vehicle structures (UAV)
Fatigue Crack Growth Prediction in a Nickel‑Base Superalloy Under Spectrum Loads Using FRANC3D
No full textIn this study, the fatigue crack growth behavior in an aero-engine material under a standard spectrum load sequence was predicted using FRANC3D and compared with available experimental results. Finite-element model of a compact tension (CT) specimen of GTM720 nickel-base superalloy was created using HYPERMESH pre-processor and an initial through thickness elliptical crack of 2.0 mm in length from the notch root was inserted in the FRANC3D environment. The local model (cracked region) along with global model (entire CT specimen) was then analyzed for fatigue crack growth behavior under a standard cold-TURBISTAN spectrum load sequence using FRANC3D in conjunction with MSC NASTRAN. Bilinear fatigue crack growth (FCG) law for the material GTM720 was derived from the earlier experimental constant amplitude fatigue crack growth rate data and used in the analysis. The stress intensity factor was calculated by M integral method. The SIFs at the crack front determined for an applied static load of 15 kN was closely matching with analytically determined SIFs. The predicted fatigue crack growth behavior trend was similar to experimental results. The total crack growth life predicted was about 42 blocks and conservative as against 46 blocks observed in earlier experimental work. The FRANC3D prediction was almost similar to earlier prediction made using in-house codes as well. Use of other crack growth laws and incorporation of load interaction effects during prediction may further improve the prediction accuracy
Heterostructure Fe2O3–In2O3 Nanoparticles as Hydrogen Gas Sensor
No full textFe2O3–In2O3 (9:1 mol.%) heterostructure nanoparticles were prepared by the thermal decomposition of stoichiometric
amounts of Fe2C2O4 2H2O and In(OH)3 at 400°C for 20 h. The sample was characterized by x-ray difraction (XRD), Fouriertransform infrared spectrometry, thermogravimetry–diferential thermal analyzer, scanning electron microscopy/transmission electron microscopy, and a superconducting quantum interference device magnetometer. The XRD pattern could be indexed to both the rhombohedral α–Fe2O3 and cubic bixbyite In2O3 phases. This heterostructure system showed ferromagnetic properties (due to the presence of γ–Fe2O3 phase) from 5 to 300 K and a spin-glass-like behavior of magnetization versus temperature under zero-feld-cooled and feld-cooled conditions. H2 gas-sensing property was observed from 100 ppm to 2 ppm at 200 °C and 250 °C. Response and recovery times were about 275 s and 500 s, respectively, and the sensitivity varied from 2% to 21% as the H2 increased from 2 to 100 ppm. The Ra/Rg varied from 1 to 1.3 and the plot of Ra/Rg versus H2 could be fitted to the sigmoidal logistic function, y = A2 + (A1− A2) / (1 + (x/x0)p
Photostable transparent wood composite functionalized with an UV-absorber
No full textTransparent wood composite (TWC) is an emerging material which combines good optical and mechanical properties with potential applications in smart windows, energy efficient building elements and solar energy concentrators etc. UV resistance of TWC is important for its suitability to be used in outdoor applications as a building material. In this study, functional TWC was prepared by lignin modification bleaching of poplar wood veneers followed by infiltration with epoxy resin doped with an UV absorber (2-(2H-Benzotriazol-2-yl)-4, 6-di-tert-pentylphenol) (conc. 1.0 and 1.75% w/v). Highly stable TWC (thickness 2 mm) with high optical transmittance was fabricated. The photostability of TWC was evaluated by exposing TWC sheets to a UVA340 fluorescent lamp in an accelerated weathering tester. For a comparison, wood, bleached wood, and epoxy samples were also subjected to UV light irradiation and the extent of degradation was evaluated by measuring colour change (yellowness index measured using spectrocolorimeter), chemical changes (monitored using FTIR spectroscopy) and optical transmittance. TWC was highly sensitive to UV light exposure and exhibited rapid photo-discolouration, chemical degradation and a decrease in optical transmittance. Incorporation of UV absorber in epoxy resin considerably reduced discolouration and photo-degradation of TWC. Moisture absorption behaviour (water uptake) of TWC was also evaluated by immersing it in water. The results indicated that TWC undergoes significant photo-degradation and needs application of UV stabilizer for its outdoor applications
High temperature ceramic radomes (HTCR) – A review
No full textAn electromagnetically transparent, structurally robust and environmentally resistant enclosure of radar antenna for ground based systems to modern avionics in military aircraft and missiles is called as radome. Radome materials are classified based on: (i) type of function - surface-based or flight-mode and (ii) speed of operation - subsonic, supersonic to hypersonic. The desired properties of these materials are low dielectric constant and low loss factor in addition to its capacity to withstand the high temperature of operation. Composite laminates of glass or aramid fibre reinforced polymeric resins are radome material candidates for applications in subsonic range. However, ceramics are the only viable option for military aerospace applications such as a fighter jet travelling at Mach 3 or an advanced hypersonic missile speeding up to Mach 5. This review outlines the hand-full of ceramic materials already in application as radome materials like high-purity-alumina, pyroceram, slip-cast-fused-silica, their processing technology, electromagnetic and mechanical properties, advantages and disadvantages with respect to advanced military vehicles. Use of silicon nitride based radome materials, that has exceptional mechanical strength and thermal stability up to 1400 °C is illustrated with respect to reaction bonded silicon nitride, hot pressed silicon nitride, silicon oxynitride, sialon and their composites. Design of new generation radome materials was conceptualized and discussed as applicable to silicon nitride and related ceramics, wherein incorporation of varied degree of porosity improves electromagnetic properties, simultaneously, maintaining the required mechanical strength. Multilayer and graded porosity and its influence on electromagnetic properties were briefly discussed. Si3N4 ceramics having controlled porosity leading to optimum electromagnetic and mechanical properties produced through systematic processing is proposed as the futuristic high temperature radome material for supersonic applications
Design and development of GMR based low range pressure sensor for medical ventilator application.
No full textIn this report, we present a thermally compensated low range magnetic pressure sensor. The fabricated sensor consists of a corrugated stainless steel (SS) diaphragm, a permanent magnet, a giant magnetoresistance (GMR) sensor, and a signal conditioning unit. The diaphragm with a permanent magnet produces a magnetic field which changes under the exposure of external pressure. The GMR sensor is placed asymmetrically with reference to the cylindrical axis of a magnet, which results in an output voltage proportional to external pressure. Simulations were performed to optimize the design having a linear output with higher sensitivity of the order of 14.97 μV/V/mbar, which is close to the experimentally measured value of 13 μV/V/mbar at room temperature. The sensor prototypes were fabricated in pressure ranges: ± 30 and ± 70 mbar. The fabricated pressure sensor prototypes were tested in different temperature ranges and calibrated for offset, linearity, and thermal variations using a commercial sensor signal conditioner. The performance of the calibrated sensors was evaluated at different temperatures and over an extended period. Furthermore, the performance of the sensor was experimentally evaluated in an indigenously developed medical ventilator, and compared with an existing commercial MEMS pressure sensor for a longer duration. The performance of the prototype sensor was found to be equivalent with an accuracy of ±0.1 mbar for an operation in the range of ± 30 mbar
On the origin of spectrally selective high solar absorptance of TiB2-based tandem absorber with double layer antireflection coatings
No full textDespite significant efforts in developing tandem ceramic coatings for photo-thermal conversion applications, the underlying physics behind spectrally selective high absorptance and thermal stability of the ceramic absorbers remains to be addressed. In this perspective, TiB2/Ti(B,N)/SiON/SiO2 and Ti/TiB2/Ti(B,N)/SiON/SiO2 films were developed on stainless steel substrates (SS 304) using pulsed direct current and radio frequency magnetron sputtering. The addition of double layer antireflection coating not only increases the solar absorptance, but also the thermal stability of the tandem absorber. The amorphous coatings exhibit a high solar absorptance of 0.981 at room temperature and an acceptable thermal emissivity of 0.15 at 82 °C. Variable angle spectroscopic ellipsometry analysis reveals a gradient in the refractive indices of the individual layers from the substrate to the top surface. The coatings with and without titanium interlayer were found to be stable for 2 h in air up to 450 °C and 400 °C, respectively. Under vacuum, the coatings exhibited good thermal stability up to 250 h at 500 °C. We make an attempt to explain the high absorptance of the tandem absorber in terms of the composition and gradient in refractive indices across the stack
On the origin of spectrally selective high solar absorptance of TiB2-based tandem absorber with double layer antireflection coatings
No full textDespite significant efforts in developing tandem ceramic coatings for photo-thermal conversion applications, the underlying physics behind spectrally selective high absorptance and thermal stability of the ceramic absorbers remains to be addressed. In this perspective, TiB2/Ti(B,N)/SiON/SiO2 and Ti/TiB2/Ti(B,N)/SiON/SiO2 films were developed on stainless steel substrates (SS 304) using pulsed direct current and radio frequency magnetron sputtering. The addition of double layer antireflection coating not only increases the solar absorptance, but also the thermal stability of the tandem absorber. The amorphous coatings exhibit a high solar absorptance of 0.981 at room temperature and an acceptable thermal emissivity of 0.15 at 82 °C. Variable angle spectroscopic ellipsometry analysis reveals a gradient in the refractive indices of the individual layers from the substrate to the top surface. The coatings with and without titanium interlayer were found to be stable for 2 h in air up to 450 °C and 400 °C, respectively. Under vacuum, the coatings exhibited good thermal stability up to 250 h at 500 °C. We make an attempt to explain the high absorptance of the tandem absorber in terms of the composition and gradient in refractive indices across the stack