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Automatic estimation of mechanical properties from fractographs using optimal anisotropic diffusion and Voronoi tessellation
No full textWith the advent of materials informatics there is a high demand of establishing automatic structure-property correlationship of materials which is a popular research topics due to the advancement of image processing and pattern recognition algorithms. Therefore, in this work, an attempt is made to estimate mechanical properties (i.e. yield strength and ductility) of AISI 304LN stainless steel from the SEM images of fracture surfaces obtained from tensile tests carried out at different strain rates using image processing techniques. As the void morphologies of fracture surfaces change systematically with the change in strain rates, the automatic detection of voids and geometrical features estimation from detected voids from the obtained are key goals of this present study. Therefore, in this work, a novel method of optimal anisotropic diffusion technique along with contrast limited adaptive histogram equalization (CLAHE), Otsu's optimal thresholding and morphological thinning operation are applied over the fractographs for edge enhancement, overcoming inhomogeneous illumination, edge segmentation and thinning, respectively, to detect voids, automatically. Then, Voronoi tessellation technique, which is a geometrical texture analysis, is utilized on these edge images of fractographs to extract four features viz. Voronoi edges, mean area, mean elongation and mean perimeter of Voronoi polygons where the linear correlation values (R2) with mechanical properties are found in the range of 0.90–0.99. A high linear correlation of features (i.e. 0.97–0.99) with the ductility is noticed as
ductility is a geometrical parameter measured during fracture
Design of high transonic axial compressor stage for small gas turbine applications
Get PDFIn the quest for achieving high performance, gas turbine engines demand efficient design of various engine components, mainly the compressor stages. The compressor stages consume most of the energy produced by the engine to provide the required pressure ratio. CSIR-NAL is involved in the development of a small gas turbine engine for UAV applications. In this regard, a high transonic single stage axial flow compressor is designed with a mass flow of 4.6 kg/s and pressure ratio of 1.6, for technology demonstration. In this paper, the aerodynamic and structural design of a high transonic axial compressor stage is discussed along with its performance characteristics. Preliminary mean-line design of the compressor stage is carried out, followed by detailed 3D blade design. Aerodynamic performance of the compressor stage is investigated numerically. Grid independency study is carried out, and the flow un-altering grid is used for steady simulations. Steady 3D RANS CFD simulations with SST turbulence model are carried out for estimating the compressor stage performance. At the design speed, the compressor is able to produce the desired pressure ratio and efficiency. Detailed flow investigations across the compressor stage are studied from choke to near stall flow conditions for different speeds. The compressor rotor blisk made of titanium alloy (Ti6AL4V) is subjected to stress analysis. The von-Mises stress and radial deformation are observed to be well within the safe limits of the chosen material. Modal analysis is carried out to study the structural dynamics of the rotor
Experimental studies on the effect of leading-edge tubercles on laminar separation bubble
No full textAn experimental investigation was carried out to study the influence of incorporating undulations (tubercles) at the leading edge of a NACA 4415 airfoil at a low Reynolds number of 120,000. Measurements were carried out at angles of attack of 6, 12, and 18 deg, which encompasses
prestall (6 and 12 deg) and poststall (18 deg) regimes of the baseline, respectively. The aerodynamic performance of the NACA 4415 airfoil with leading-edge tubercles was compared against an airfoil without tubercles (baseline) through pressure measurements. Additionally, surface oilflow visualization and two-dimensional (2-D) particle image velocimetry (PIV) were carried out to obtain insight into the on-surface flow topology and off-body flowfield of the modified and baseline airfoils. At the lower angle of attack (a = 6 deg), the extent of the laminar separation bubble (in both length and height), which was the dominant flow feature over the baseline airfoil, was significantly altered by the presence of tubercles at the leading edge. The addition of tubercles resulted in the formation of pockets of smaller separation bubbles instead of one single long bubble spread along the span observed in the baseline airfoil. The 2-D PIV and oil-flow visualization results at an angle of attack of 18 deg prove that the tubercles are very much effective beyond the stall conditions of the baseline airfoil. The modified airfoil maintained attached flow until 50% of the chord, instead of complete separation starting from the leading edge, as noticed for the baseline case. The size of the recirculating zone downstream of the separation was also significantly reduced by the tubercles. All these factors contribute to the increased performance of the airfoil with leading-edge tubercles, especially at poststall angles of the baseline
Experimental investigation of droplet velocity fields from elliptic injectors in subsonic cross flow
No full textThe flow field associated with a liquid jet injected transversely into a crossflow, also referred as transverse jet has numerous applications in industrial, environmental and natural systems. Examples of these applications include air-breathing engines (gas turbine afterburners, ramjet and scramjet combustors), rocket engines, environmental control systems and natural flows. Earliest research of a jet in a crossflow has been motivated by applications related to environmental problems such as plume dispersal from exhaust or pipe stacks or liquid effluent dispersal in streams. This method of liquid fuel/air mixture preparation enhances flame stabilization, fuel conversion efficiency, and reduction in emissions. In gas turbine applications because of the very limited residence time available for effective fuel air mixing, detailed investigations into spray characteristics of different injector configurations in a crossflow environment is desirable for identifying promising configurations with measurements in the near field to acquire reliable spray data for development of CFD models. The velocity field of a liquid jet in the near field ejecting out from an elliptic injector into a crossflow of air were investigated experimentally at conditions relevant to gas turbine applications. A rig was set up to investigate the injection of liquid jet in subsonic cross flow with a rectangular test section of cross section measuring 100 mm by 140 mm. Experiments were done with a two injector configurations a circular 0.8mm diameter plain orifice injector and a elliptic injector with an equivalent effective area of 0.7 mm (minor axis) by 0.95 mm (major axis) which was flush mounted on the bottom plate of test section. PIV technique was used to measure droplet velocity field and distributions in the near field of the spray. Measurements were performed at a distance of 5 mm from the bottom wall in the span wise plane and the results were compared with a circular injector. It was seen that no significant differences were observed in the u and v velocity components for the elliptic and circular injectors where the geometry changes are small suggesting that parameters like velocity are not significantly affected by small changes in injector exit geometry. Further for elliptic jets it was observed that increasing the crossflow velocity and maintaining the same liquid flow rate lead to an increase in the lateral spread of the spray with no significant change in the mean vorticity values
Fatigue Analysis of Wing-Fuselage Lug section of a Transport Aircraft
No full textLug joints are special type of pin joints, which are widely used for joining various parts of an aircraft, especially for joining wings to fuselage. During service, the lug type joints are subjected to fatigue loading and complete load transfer takes place through the pin. At the pin and lug interface, the combination of high stress concentration and fretting could potentially lead to crack initiation and then crack propagation under cyclic loading. Because of this reason the wing-fuselage lug joints are considered as most fracture critical components in the aircraft structure. To appraise the safety level of lugs under working conditions, fatigue crack growth and residual life data are required.In the present work, a computational model for estimating the
residual fatigue life of attachment lugs has been proposed. The pin is assumed to have a larger stiffness than the lug. The pin is assumed to be fit in the lughole with zero clearance and no frictional restraint. Initially stress concentration effects in the loaded lug were determined by applying analytical and numerical methods. Stress intensity factor for the pin loaded lug with through-the-thickness emanating from the lug hole has been determined. Both analytical and numerical methods have been used for
obtaining the stress intensity factor. Further, fatigue crack growth life for the cracked lug subjected to constant amplitude cyclic loading was estimated using the Walker’s crack growth model. Also the effect of different radius ratios (lug geometry) on the number of cycles to failure is studied. For the FE analysis MSC Nastran/Patran softwares have been used
Constitutive modeling of smart adaptive composite with inactive SMP
No full textQuite amazingly, materials of a certain class popularly named as smart materials are capable of responding to an external stimulus. Shape memory effect is the property of some of these material to gain back its original shape when activated with suitable stimulus. Shape memory alloys (SMAs) are metals, which exhibit two very unique properties, pseudo-elasticity, and the shape memory effect. The polymers which exhibit shape memory effect are called shape memory polymers. A shape memory composite (SMC) can be created by combining two or more materials involving at least one shape memory material. The presented work aims at the development of a mathematical constitutive model for a SMC of SMA wires in SMP matrix. The mathematical model has been developed using the rule of mixtures for composites and the material property curves have been generated for the SMC for various thermo mechanical loading and unloading cycles using
Matlab
Sub-wavelength waveguide properties of 1D and surfacefunctionalized SnO 2 nanostructures of various morphologies
No full textOne-dimensional (1D) SnO 2 sub-wavelength waveguides are a critical contribution to advanced optoelectronics. Further understanding of the surface defects and role of morphology in 1D SnO 2 nanowires can help to better utilize these nanostructures more efficiently. For this purpose, three different nanowires (NWs), namely belts, cylindrical- and square-shaped structures were grown using SnO 2 quantum dots as a precursor material. The growth process of these NWs is discussed. The nanobelts were observed to grow up to 3 mm in length. Morphological and structural studies of the nanostructures were also carried out. All NWs showed waveguide behavior with visible photoluminescence (PL) upon excitation with a 325 nm laser. This behavior was also demonstrated in tapered and surface-functionalized SnO 2 NWs. While the tapered waveguide can allow for easy focusing of light, the simple surface chemistry offers selective light propagation by tuning the luminescence. Defect-related PL in NWs is studied using temperature-dependent measurements and a band diagram is proposed
The key role of thread and needle selection towards ‘through-thickness reinforcement’ in tufted carbon fiber-epoxy laminates
No full textTufting of dry preforms is one of the means of accomplishing through-thickness reinforcement (TTR) in a liquid composite molding process. Herein, once a preform is laid up, an automated robotic tufting setup is used to introduce the TTR. The selection of thread and needle for tufting process go hand-in-hand as tufting operation involves the act of penetrating preform by the needle as well as the trauma thread has to endure during this act. This paper explores the methodology of thread and needle selection through studies at different levels right from tufting of preforms to testing of tufted laminates. Glass, carbon and Kevlar threads in combination with a tufting needle and two different sewing needles are explored in this study. The effect of tufting speed on the quality of tuft is analyzed in terms of damage of fabric yarn, thread, and needle breakage. Layer-wise analysis of damage due to needle penetration in fabric yarns is carried out. Key mechanical properties of tufted composite samples are evaluated to determine the effect of tufting on the in-plane and out-of-plane properties
Solution combustion synthesis of calcia-magnesia-aluminosilicate powder and its interaction with yttria-stabilized zirconia and co-doped yttria-stabilized zirconia.
No full textThermal Barrier Coatings (TBCs) play a significant role in improving the efficiency of gas turbines by increasing their operating temperatures. The TBCs in advanced turbine engines are prone to silicate particles attack while operating at high temperatures. The silicate particles impinge on the hot TBC surfaces and melt to form calciamagnesia-aluminosilicate (CMAS) glass deposits leading to coating premature failure. Fine powder of CMAS with the composition matching the desert sand has been synthesized by solution combustion technique. The present study also demonstrates the preparation of flowable yttria-stabilized zirconia (YSZ) and cluster paired YSZ (YSZLn2O3, Ln =Dy and Gd) powders by single-step solution combustion technique. The as-synthesized powders have been plasma sprayed and the interaction of the free standing TBCs with CMAS at high-temperatures (1200 °C, 1270 °C and 1340 °C for 24h) has been investigated. X-ray diffraction analysis of CMAS attacked TBCs revealed a reduction in phase transformation of tetragonal to monoclinic zirconia for YSZ-Ln2O3 (m-ZrO2: 44%) coatings than YSZ (m-ZrO2: 67%). The field emission scanning electron microscopic images show improved CMAS resistance for YSZ-Ln2O3 coatings than YSZ coatings
Experimental investigation of fluid–structure interaction in a bird-like flapping wing
No full textFluid–structure interaction in a bird-like flapping wing is investigated experimentally. Various materials having varied thickness (t), elastic property (E) and density (ρw) are selected as the wing for the flapping motion. Force and power measurements are performed in wind-off condition for a range of flapping frequencies. The effect of rib orientation, position of the single spanwise rib along the wing chord and multiple spanwise ribs on thrust generation is also investigated. Dynamics of the flow around different wing configurations are elucidated based on Phase-locked 2D Particle Image velocimetry (PIV) measurements. We found that the strength and size of trailing edge vortex (TEV) are closely related to the stiffness characteristics of the wing. The strength and size of TEV are found to increase with an increase in the stiffness of the wing. Based on thrust generation and TEV characteristics, we noted that the effect of rib is not identical for two different wing materials. The non-dimensional stiffness (Πe∗) for various wing without rib configurations is calculated. We found a non-linear correlation between coefficient of thrust (CT∗) and non-dimensional stiffness (Πe∗) for specific wing configurations. The major findings from this study suggest that wing stiffness cannot be the sole factor influencing the thrust generation. Apart from the wing stiffness, wing deformation especially the trailing edge (TE) deformation pattern might have a major role in thrust generation and there is a need to quantify the deformation either experimentally or computationally