Browsing by Author "Udaya, B.K."

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5,10,15,20-Tetrakis(p-tolyl)porphyrin derived carbon dots as colorant in flexo and screen inks with multi-level covert features for security printing
(Elsevier B.V., 2024) Ullal, N.; Sahoo, B.; Dhanya, D.; Kulkarni, S.D.; Sinha, R.K.; Anand, P.J.; Udaya, B.K.
Fluorescent inks with covert security features, which make it difficult for forgers to replicate, are highly sought after among the array of anti-counterfeit technologies. The present study focuses on the synthesis of Carbon dots (CDs) from 5,10,15,20-tetrakis(p-tolyl)porphyrin (TTP) via a solvothermal approach. The prepared CDs exhibit attractive emissive characteristics with an absolute fluorescence quantum yield of 38.85 %. Time-resolved fluorescence studies reveal the multiple exponential decay nature of the emitters, which could be due to the diverse chemical environment on the surface of the CDs. XPS analysis proves oxygen as the major element, along with carbon, sulfur, and nitrogen as minor elements. DFT studies on four optimized structures of CDs along with their respective UV and FT-IR plots are conducted. The theoretically derived photoluminescence plots corresponding to the 25-30th excited states coincide with the experimental emission peak. CDs demonstrate characteristic variations in fluorescence in the presence of water, attributed to ?-? stacking induced aggregation. Aggregate formation is also influenced by pH changes, affecting the surface functional groups in proximity to the solvent medium. CDs are used as colorants in the fabrication of both flexo and screen inks. Flexo ink retains the fluorescence features of the CDs, while screen ink offers multilevel security features. Exposing UV-dull paper to 365 nm UV light allows the ink inscribed letters to appear fluorescent blue, whereas the use of UV/green optical filters facilitates the visualization of green/yellow emissions. The introduction of multilevel features makes the duplication of the print difficult, protecting the integrity of the product and could be used for real-life applications. © 2024 The Author(s)
Effect of Microstructure on the Fatigue Crack Growth Behavior in Alâ€“Znâ€“Mgâ€“Cu Alloy
(Springer Science and Business Media Deutschland GmbH, 2020) Nandana, M.S.; Udaya, B.K.; Manjunatha, C.M.
High-strength Alâ€“Znâ€“Mgâ€“Cu alloys are used in airframe structures, such as bulk heads, wing spars, and lug joints. In this investigation, the effect of RRA microstructure on the fatigue crack growth rate (FCGR) behavior is studied. The 7010 aluminum alloy was heat treated to two different conditions, i.e., T6 and RRA. The microstructure of the heat-treated alloy is characterized by using transmission electron microscope (TEM). The FCGR tests were performed as per ASTM E647 standard by using a 100Â kN servo-hydraulic test machine. The tests were performed using standard compact tension (CT) specimens with a stress ratio, R = 0.7 using a sine wave form at 10Â Hz in a standard laboratory air environment. The matrix microstructure of the RRA-treated alloy consists of fine scale Î·Â´ (MgZn2) precipitates with increased interparticle spacing when compared to closely packed Î·Â´ precipitates in the standard T6-treated alloy. The grain boundary precipitates are coarsened and discrete in the RRA-treated alloy, while it is continuous in T6 condition. An improvement in the threshold stress intensity factor range (Î”Kth) by about 0.65Â MPaâˆšm is observed in RRA-treated alloy compared to the T6-treated alloy. The FCGR was observed to be lower by 2 times in RRA-treated alloy compared to T6-treated alloy over the major portion of FCGR curve. The increased free slipping distance between the matrix precipitates in RRA-treated alloy is correlated to the improved fatigue crack growth resistance of the RRA-treated aluminum alloy. Â© 2020, Springer Nature Singapore Pte Ltd.
Effect of Microstructure on the Fatigue Crack Growth Behavior in Al�Zn�Mg�Cu Alloy
(2020) Nandana, M.S.; Udaya, B.K.; Manjunatha, C.M.
High-strength Al�Zn�Mg�Cu alloys are used in airframe structures, such as bulk heads, wing spars, and lug joints. In this investigation, the effect of RRA microstructure on the fatigue crack growth rate (FCGR) behavior is studied. The 7010 aluminum alloy was heat treated to two different conditions, i.e., T6 and RRA. The microstructure of the heat-treated alloy is characterized by using transmission electron microscope (TEM). The FCGR tests were performed as per ASTM E647 standard by using a 100�kN servo-hydraulic test machine. The tests were performed using standard compact tension (CT) specimens with a stress ratio, R = 0.7 using a sine wave form at 10�Hz in a standard laboratory air environment. The matrix microstructure of the RRA-treated alloy consists of fine scale ?� (MgZn2) precipitates with increased interparticle spacing when compared to closely packed ?� precipitates in the standard T6-treated alloy. The grain boundary precipitates are coarsened and discrete in the RRA-treated alloy, while it is continuous in T6 condition. An improvement in the threshold stress intensity factor range (?Kth) by about 0.65�MPa?m is observed in RRA-treated alloy compared to the T6-treated alloy. The FCGR was observed to be lower by 2 times in RRA-treated alloy compared to T6-treated alloy over the major portion of FCGR curve. The increased free slipping distance between the matrix precipitates in RRA-treated alloy is correlated to the improved fatigue crack growth resistance of the RRA-treated aluminum alloy. � 2020, Springer Nature Singapore Pte Ltd.
Engineering Architectures for Biofuel Cells
(wiley, 2023) Udaya, B.K.; Bhat Panemangalore, B.P.
Biofuel cells employing microorganisms as biocatalysts provide an environment-friendly fuel cell configuration. When miniaturized the biofuel cell becomes an attractive candidate for powering small devices like portable electronic devices, biological sensors and implantable medical devices, etc. A lot of research has gone into exploring various types of biocatalysts, their performance, architectural designs, their benefits and limitations and this chapter reviews them. Various components of architectural design in the fuel cell is discussed. A brief review on experimental tools used in characterisation of these systems is included. © 2021 Scrivener Publishing LLC.
Facile and rapid method to synthesis sulfur and nitrogen co-doped graphene quantum dots as an electrode material with excellent specific capacitance for supercapacitors application
(Elsevier Ltd, 2024) Muhiuddin, M.; Devi, N.A.; Bharadishettar, N.; Meti, S.; Siddique, A.B.; Satyanarayan, M.N.; Udaya, B.K.; Akhtar, W.; Rahman, M.R.
The current invention pertains to the expeditious simple synthesis of electrode materials that improve the storage capacity of supercapacitors (SCs). Sulfur and nitrogen co-doped graphene quantum dots (SN-GQDs) are synthesized using a microwave-assisted hydrothermal (MAH) process at low pressure and with a short reaction time. The utilization of SN-GQDs in conjunction with Polyaniline (PANI) has the potential to enhance the supercapacitor's energy and power density, owing to their notable specific capacitance. Implementing SN-GQDs material as an SCs electrode, exhibiting an outstanding specific capacitance of 1040 F/g at an applied current density of 0.5 A g−1. Furthermore, a composite of SN-GQDs/PANI is synthesized and the electrochemical performance is compared with the as-synthesized PANI. The symmetrical SCs are fabricated using SN-GQDs/PANI composite, and PANI. At a current density of 0.5 A g−1 SN-GQDs/PANI composite-based SC displays a superior energy density of 44.25 Wh/kg at a power density of 1.227 kW/kg. This is high in comparison to PANI-based SC which shows an energy density of 18.71 Wh/kg at 0.8 kW/kg power density at the same current density. The SC created using SN-GQDs/PANI composite exhibits superior properties and is a promising material for SC applications. © 2024 Elsevier B.V.
Influence of heat treatment on near-threshold fatigue crack growth behavior of high strength aluminum alloy 7010
(2020) Nandana, M.S.; Udaya, B.K.; Manjunatha, C.M.
In this study, aluminum alloy 7010 was subjected to three different ageing treatments i.e., peak ageing (T6), over ageing (T7451) and retrogression and re-ageing (RRA) to study the influence of precipitate microstructure on the fatigue crack growth rate (FCGR) behavior. The microstructural modifications were studied by using TEM to examine the change in size and morphology of the precipitates. The size of the precipitates in the matrix range from 16-20nm in T7451, 5-6nm in RRA and 2-3nm in T6 alloys, respectively. The FCGR tests were performed on standard compact tension (CT) specimens as per ASTM E647 standard in a computer controlled servo-hydraulic test machine with applied stress ratio, R = 0.1 and loading frequency of 10 Hz. The crack growth was measured by adopting compliance technique using a CMOD gauge attached to the CT specimen. The fatigue crack growth rate was higher in T7451 and lowest in RRA treated alloy. The RRA treated alloy showed higher (formula presented) compared to T7451 and T6 treated alloys. The measured (formula presented) was 11.1, 10.3 and (formula presented) in RRA, T6 and T7451 alloys, respectively. In the near-threshold regime, the RRA treated alloy exhibited nearly 2-3 times reduction in the crack growth rate compared to the T6 alloy. The growth rate in the RRA alloy was one order lower than that of the T7451 condition. The surface roughness of RRA treated alloy was more pronounced. The reduction in FCGR observed in RRA alloy was correlated to partial crack closure due to tortuous crack path and partially due to increased spacing between the matrix precipitates. The reduction in near-threshold FCGR and increase in (formula presented) is expected to benefit the damage tolerant capability of the aircraft structural components under service loads. � Springer Nature Switzerland AG 2020.
Influence of heat treatment on near-threshold fatigue crack growth behavior of high strength aluminum alloy 7010
(Springer Science and Business Media Deutschland GmbH, 2020) Nandana, M.S.; Udaya, B.K.; Manjunatha, C.M.
In this study, aluminum alloy 7010 was subjected to three different ageing treatments i.e., peak ageing (T6), over ageing (T7451) and retrogression and re-ageing (RRA) to study the influence of precipitate microstructure on the fatigue crack growth rate (FCGR) behavior. The microstructural modifications were studied by using TEM to examine the change in size and morphology of the precipitates. The size of the precipitates in the matrix range from 16-20nm in T7451, 5-6nm in RRA and 2-3nm in T6 alloys, respectively. The FCGR tests were performed on standard compact tension (CT) specimens as per ASTM E647 standard in a computer controlled servo-hydraulic test machine with applied stress ratio, R = 0.1 and loading frequency of 10 Hz. The crack growth was measured by adopting compliance technique using a CMOD gauge attached to the CT specimen. The fatigue crack growth rate was higher in T7451 and lowest in RRA treated alloy. The RRA treated alloy showed higher (formula presented) compared to T7451 and T6 treated alloys. The measured (formula presented) was 11.1, 10.3 and (formula presented) in RRA, T6 and T7451 alloys, respectively. In the near-threshold regime, the RRA treated alloy exhibited nearly 2-3 times reduction in the crack growth rate compared to the T6 alloy. The growth rate in the RRA alloy was one order lower than that of the T7451 condition. The surface roughness of RRA treated alloy was more pronounced. The reduction in FCGR observed in RRA alloy was correlated to partial crack closure due to tortuous crack path and partially due to increased spacing between the matrix precipitates. The reduction in near-threshold FCGR and increase in (formula presented) is expected to benefit the damage tolerant capability of the aircraft structural components under service loads. Â© Springer Nature Switzerland AG 2020.