Faculty Publications
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Item Blue light emitting naphthalimides for organic light emitting diodes(2013) Ulla, H.; Garudachar, B.; Satyanarayan, M.N.; Umesh, G.; Isloor, A.M.The photophysical, electrochemical, surface morphology and thermal properties of two novel blue lightemitting materials were studied. Results indicate that the molecules offer potential as non-doping light-emitting materials with good electron injection capabilities for fabrication of blue organic light-emitting diodes. © 2013 American Institute of Physics.Item Thermal induced motion of functionally graded beams subjected to surface heating(Ain Shams University, 2018) Malik, P.; Kadoli, R.Thin beam of the functionally graded (FG) type subjected to a step heat input on one surface and insulated or exposed to convective heat loss on the opposite surface is under consideration for the evaluation of thermal induced motion. The dynamic displacement and dynamic thermal moment of the beam are analysed when the temperature gradient is independent of the beam displacement. The power law index dictates the metal–ceramic distribution across thickness of the beam and its effect on the thermal vibration of the beam is examined. The article discusses, in depth, the influence of various factors such as length to thickness ratio of beam, heat transfer boundary conditions, physical boundary conditions, and metal–ceramic combination on the thermal oscillations of FG beam. It is found that attenuation of the amplitude of static thermal deflection and superimposed thermal oscillations is a strong function of the metal–ceramic combination for the FG beam. © 2015 Faculty of Engineering, Ain Shams UniversityItem Biodegradation of PEEK Piston Rings(Elsevier Ltd, 2021) Shetty, P.; Dsilva, P.; Sondar, P.R.; Kumar, B.G.; Hegde, S.Polyether ether ketone (PEEK) is considered a high performance thermoplastic with excellent mechanical, chemical, and thermal properties. It is generally believed that this material is chemically and biologically inert, and is used for various biomedical and industrial applications, especially in the form of fiber reinforced polymeric composites. Contrary to the general belief, the present work reports the biodegradation of PEEK piston rings that were used in a reciprocating CO2 compressor. A series of circumstantial and direct evidences were collected by following various tests and characterization methods to confirm the degradation of the piston rings by bacterial attack. The bacterial cells were extracted from the degraded piston rings, cultured in agar medium and then studied using scanning electron microscope. An experimental simulation was carried out by depositing and incubating a bacterial culture on the pristine surface of a PEEK specimen. The simulation experiment revealed an early stage of bacterial degradation in the form of cracking of the PEEK specimen surface. The results of various tests, characterization, and the experimental simulation presented in the paper suggest that PEEK based composites degrade due to enzymatic hydrolysis process by Myxococcus Xanthus, the rod–shaped soil bacteria. © 2021Item Effect of manganese and homogenization on the phase stability and properties of Cu–Al–Be shape memory alloys(Elsevier Editora Ltda, 2021) Bala Narasimha, G.; Murigendrappa, S.M.In this study, the effect of addition of manganese to the ternary Cu–Al–Be shape memory alloys on phase stability, phase transformation temperatures, microstructure, morphology and grain size has been investigated. Secondly, the effect of betatization temperatures and time period has been investigated on the phases and properties of Cu–Al–Be–Mn SMAs. Results reveal that the addition of manganese in the alloys with Al ? 11.8 wt.% forms coexistence of ?1? and ?1? martensites, and manganese ?1 wt.% forms austenite ?1 (DO3). DSC studies exhibit two stage reverse transformation attributes to coexistence of martensites. Increase in manganese decreases the transformation temperatures and increase in betatization temperature and time increases transformation temperatures. Alloying manganese didn't exhibit significant grain refinement and results reduced shape recovery due to the coexistence of martensites. © 2021 The Author(s)Item Influence of oxidation on fracture toughness of carbon-carbon composites for high-temperature applications(Gruppo Italiano Frattura, 2021) Sunil Kumar, B.V.S.; Londe, V.N.; Lokesha, M.; Vasantha Kumar, S.N.; Surendranathan, A.O.Carbon-Carbon Composites (C-CC), used as composites for their remarkable qualities in the space industry and in many other industry sectors. C-CC has proven to be the most efficient material in extreme temperature situations. They are one among the best high-temperature materials with good thermal quality, such as high-temperature stability, outstanding thermal conductivity and low-temperature expansion coefficients. In aircraft, railways, trucks and even race vehicles, C-CC brake disks are in high demand. Compared to the favorable thermal and mechanical qualities of C-CC, their great sensitivity to oxidation in an oxidizing environment at temperatures even around 400°C is a major restriction with these composites. In particular, a study of the C-CC oxidation mechanism helps to create protective measures for these composites. The present experimental study explores the influence of oxidation in static air on the fracture toughness of C-CC. At a temperature of around 400°C to 700°C in an increment of 100°C, an oxidation evaluation of the material is carried out. Results show that there was a significant decrease in the fracture toughness when there was an increase in temperature from 400°C to 700°C. We can observe that C-CC fracture toughness is severely affected by oxidation. The decrease in the fracture toughness value in comparison with room temperature was 6% for 400°C and 45% for 700°C. © 2021.Item Improving the: ZT of SnTe using electronic structure engineering: Unusual behavior of Bi dopant in the presence of Pb as a co-dopant(Royal Society of Chemistry, 2021) Shenoy, U.S.; Bhat, D.K.Electronic structure engineering of SnTe by doping various elements to improve its figure of merit has been the most promising approach recently sought after. Pb doped in SnTe is well known to decrease the thermal conductivity but fails to beneficially tune its electronic properties. Herein, we co-dope Bi in SnTe doped with Pb, to improve the power factor of the material. Bi in the presence of Pb exhibits unusual features not shown in the case of Bi doped SnTe. The synergistic action leads to an increase in the band gap and valence band convergence. Bi also introduces resonance states just below the conduction band edge and causes conduction band convergence. An enhanced power factor due to modification of the electronic structure combined with reduced thermal conductivity translates into an enhanced figure of merit of up to ?1.58 at 800 K as predicted using Boltzmann transport calculations, making it a potential thermoelectric material worthy of further study. This journal is © The Royal Society of Chemistry.Item Compressive Characterization of Date Palm Leaf Fiber(Taylor and Francis Ltd., 2022) Nanda, J.; Das, S.N.; Mohapatra, A.In this present work, the surface of date palm leaf fiber has been modified by means of different chemical treatments. The thermal, morphological, mechanical, and water absorption characteristics of DPL fibers were investigated. The effect of the surface modifications of the DPL fibers was envisioned through the SEM micrographs, which shows the existence of voids and rough surfaces because of the elimination of lignin, wax, and pectin from the fiber. FTIR spectroscopy of DPL fibers was done, to check the effects of surface modifications on the fiber composition. XRD analysis confirms the improvement in crystallinity index of the surface-modified DPL fibers. The thermogravimetric analysis confirms augmentation in the thermal stability and tensile strength of the surface-modified fibers. The water absorptivity test conforms the reduction in the water absorption of the DPL fiber after surface modification. Furthermore, the DSC curve shows the temperature range for the moisture vaporization from fibers, fiber degradation, and the formation of char.key words-Natural fiber,Composite,Date palm leaf fiber,XRD,SEM,FTIR. © 2021 Taylor & Francis.Item A case of perfect convergence of light and heavy hole valence bands in SnTe: the role of Ge and Zn co-dopants(Royal Society of Chemistry, 2022) Shenoy, U.S.; D, G.K.; Bhat, D.K.A dual step approach of decreasing the thermal conductivity and improving the power factor by using two different dopants has shown great promise in the development of high performance thermoelectrics. In this work, we dope Ge, which is well known to decrease the thermal conductivity of SnTe. Later, to this, we co-dope Zn to simultaneously improve the power factor. Zn, in the presence of Ge, introduces resonance levels, thus distorting the density of states near the Fermi level, improving the room temperature performance. In addition, it is also able to increase the band gap, thus preventing bipolar diffusion at high temperatures. The unique feature exhibited is the perfect convergence of light and heavy hole valence sub-bands achieved for the first time in SnTe promising a high performance throughout the temperature range. The transport property calculations reveal that in addition to p-type, it can also act as an outstanding n-type material by tuning its chemical potential, making it worth studying experimentally. © 2022 RSC.Item Nonlinear thermo-elastic stability of variable stiffness curvilinear fibres based layered composite beams by shear deformable trigonometric beam model coupled with modified constitutive equations(Elsevier Ltd, 2023) Manickam, G.; Haboussi, M.; D'Ottavio, M.; Kulkarni, V.; Chettiar, A.; Gunasekaran, V.Nonlinear thermo-elastic buckling characteristics of composite variable stiffness beam with layers making use of curvilinear fibres under thermal environment is attempted here. The model is based on a shear deformable theory introducing trigonometric function, and considering von Kármán's assumptions based geometrical nonlinear effect. The beam constitutive equation is modified according to the stress-free situation in the width direction of beam-Poisson's effect in the formulation for predicting the behaviour of general lay-up composite beams. By the principle of minimum total potential energy, the governing equations in terms of incremental stiffness matrices are formed introducing general beam finite element. The global equilibrium equations formulated are solved for envisaging the post-buckling path through eigenvalue analysis iteratively, thus establishing the relationship of thermal temperature against moderate amplitude level of beam deflection. A systematic parametric analysis considering different lamina properties such as curvilinear fibre path angles and including lay-up sequences, thermal expansion coefficient, mixed laminate combining straight and curvilinear fibres-based layers is carried out on thermo-structural stability of curvilinear fibre-based beams. Also, the influence of geometric factors, flexible beam end support, and variation in thermal profile, etc. over the stability behaviour of beam is examined. © 2022Item Thermal resistance of Open-Cell metal foam with thermal interface materials (TIM)(Elsevier Ltd, 2023) Ganesan, P.; Zaib, F.; Zaharinie, T.; Mobedi, M.; Gnanasekaran, N.This study investigated the thermal resistances of sandwich structures consisting of open-type metal foams, base plates/surfaces, and thermal interface materials (TIMs) in two types of sandwiching configurations, namely Type 1 and Type 2. Samples were prepared using metal foam structures of 20, 40, and 60 pores per inch (PPIs), representing five commercial TIMs, i.e., pyrolytic graphite sheet (PGS), T621, SFT90, PC93, and PC94. They were categorised into two types: (i) thin and hard films (PGS, T621, SFT90) and (ii) thick and soft pads (PC93 and PC94). The thermal resistance and the thickness were measured under compression loadings of 0 – 60 N using an in-house thermal resistance tester developed according to the ASTM D5470 standard. Based on the nanoindentation test, PGS showed the highest hardness (0.2660 GPa), followed by T621 (0.0322 GPa), SFT90 (0.0235 GPa), PC93 (0.0007 GPa), and PC94 (0.0004 GPa). In general, thermal resistances were dependent on compression forces; they decreased with increasing compression loads. At a 30 N load for 60 PPI, the thermal resistance of the hard TIM sample was reduced to 62% with a 1.5% reduction in compression thickness at the Type 1 configuration. The resistance decreased as much as 8% when PPIs increased from 20 to 60. By contrast, at a 30 N load for 60 PPI, the thermal resistance of the soft TIM sample was reduced to 58% with a 16% reduction in compression thickness at the Type 1 configuration. When PPIs increased from 20 to 60, the resistance decreased by just 5%. Despite a lower thermal resistance reduction than the hard TIM, the soft TIM was 19% higher in thermal resistance difference. This study showed that joining metal foam, TIM, and base plate reduced thermal resistances while increasing their performance. © 2022 Elsevier Ltd