130 research outputs found
Cold Spray Coatings for Surface Enhancement of Inconel 718
No full textCold spray is an emerging additive manufacturing technology that is promising to be used for surface repair and enhancement. In this study, Inconel 713 coating was successfully deposited on Inconel 718 substrate using a high-pressure cold spray process. The microstructure and hardness of the coating were studied. The cold sprayed Inconel 713 coating had a very low porosity level due to the severe plastic deformation of the splats. Hardness of the coating is much higher than that of Inconel 718 substrate. The regions closer to the substrate-coating interface in the coating showed higher hardness value compared to those located further away from the interface. This phenomenon can be attributed to the peening effect during high-velocity impact of Inconel 713 particles with the Inconel 718 substrate. This study demonstrates that cold sprayed coatings have the potential to increase surface hardness and further improve wear resistance of the Inconel 718 substrate
Inconel 713C Coating by Cold Spray for Surface Enhancement of Inconel 718
No full textInconel 713C is a nickel-based superalloy usually considered as a material of poor weldability due to its susceptibility to hot cracking in the heat-affected zones. Cold spray, a solid-state deposition technology that does not involve melting, can be proposed as a methodology to deposit Inconel 713C for surface enhancement of other target components. In this study, Inconel 713C coating was deposited on Inconel 718 substrate with a high-pressure cold spray system. The coating was characterized in terms of microstructure, hardness, and wear properties. The cold-sprayed Inconel 713C coating has a low porosity level and refined grain structures. Microhardness of the Inconel 713C coating was much higher than the Inconel 718 substrate. The sliding wear tests showed that the wear resistance of the cold-sprayed Inconel 713C coating is three times higher than the Inconel 718 substrate, making the coating a suitable protective layer. The main wear mechanisms of the coating include oxidation, tribo-film formation, and adhesive wear
Strain-tuning of periodic optical devices : tunable gratings and photonic crystals
No full textThesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. [161]-173).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.The advancement of micro- and nano-scale optical devices has heralded micromirrors, semiconductor micro- and nano-lasers, and photonic crystals, among many. Broadly defined with the field of microphotonics and microelectromechanical systems, these innovations have targeted applications in integrated photonic chips and optical telecommunications. To further advance the state-of-the-art, dynamically tunable devices are required not only for demand-based reconfiguration of the optical response, but also for compensation to external disturbances and tight device fabrication tolerances. In this thesis, specific implementations of strain-tunability in two photonic devices will be discussed: the fundamental diffractive grating element, and a photonic band gap microcavity waveguide. For the first part, we demonstrate high-resolution analog tunability in microscale diffractive optics. The design concept consists of a diffractive grating defined onto a piezoelectric-driven deformable membrane, microfabricated through a combination of surface and bulk micromachining. The grating is strain-tuned through actuation of high-quality thin-film piezoelectric actuators. Device characterization shows grating period tunability on the order of a nanometer, limited by measurement uncertainty and noise. The results are in good agreement with analytical theory and numerical models, and present immediate implications in research and industry. For the second part, we generalize the piezoelectric strain-tunable membrane platform for strain-tuning of a silicon photonic band gap microcavity waveguide. Additional motivation for this strain-tuning approach in silicon photonic crystals lies in:(cont.) (a) the virtual absence of electro-optic effects in silicon, and (b) the ability to achieve tuning with low power requirements through piezoelectric actuation. Compared to current thermo-optics methods, piezoelectric actuation affords faster and more localized tuning in high-density integrated optics. The small-strain perturbation on the optical resonance is analyzed through perturbation theory on unperturbed full 3D finite-difference time-domain numerical models. Device fabrication involves X-ray nanolithography and multi-scale integration of micro- and nano-fabrication methods. Experimental characterization achieved dynamically-tunable resonances with 1.54 nm tunable range (at 1.55 Mum optical wavelengths), in good agreement with theory. This is the first demonstration of strain tunability in photonic crystals and contributes to the development of smart micro- and nano-scale photonics.by Chee Wei Wong.Sc.D
NIE Family Day 2014 (3 Oct 2014)
No full textThe Staff Welfare Recreation Fund Committee (SWRFC) Organizing Committee of Family Day. Back row, from left: Lee Li Lian Val (NSSE), Nenny Noorman (LIBRIS), Kristina Burgetova (PS), Ho Yen Yen Rebecca (NSSE), Low Li Jia (OAAS), Soo Li Mei Johannah (NSSE), Lim-Ang Ah Buan (NSSE) and Stevenson-Yong Mary Magdalene (NSSE). Front row, from left: Lionel Lim Chee Sin (NSSE), Foo Meng Wei (GPL), Chua Wee Ann (OTE) and Lum Hon Peng (CSC)
Sub-fm/Hz(1/2) displacement measurement on MgF2 whispering gallery mode microcavity
No full textWe present sub-fm/Hz(1/2) displacement measurement on the MgF2 whispering gallery mode microcavity. We analyze power spectral density of the displacement from 1 Hz to 100 kHz of the Fourier offset frequency. (C) 2020 The Author(s
Designing shallow foundation to Eurocode 7
No full textBritish Codes and Standards (BS) have been used in practice for many years and for the past few years, it is use co-existence with Eurocodes (EC) for the past few years. The whole suite of structural Eurocodes is expected to replace the current BS Codes and standards in 2010. With this replacement, practicing engineers will need to be familiar with the methodology, design philosophy and assumptions adopted in the code.
This report presents the differences in designing shallow foundations using different geotechnical codes namely BS8004, US Naval Facilities Engineering Command (NAVFAC) and EC7. The three codes are discussed and design examples will be used in making comparison between the codes.Bachelor of Engineering (Civil
Static tensile test of metal alloys
No full textThis report reviews on the Final Year Project (FYP) B186, Static Tensile Test of Metal Alloys. Aluminum 6061-T6 is used in this research and experimentation. The static tensile test was conducted, and the results would then be compared with prior FYP reports and available data.
The author studied past final year reports and familiarised with the ASTM Standards. The objective of this project is to define the mechanical properties for Aluminum 6061-T6. Similar to previous FYP, the fabrication of specimen is Computer Numerical Control (CNC) wire cutting and the experiment is performed in the longitudinal direction. Unlike past final year projects, the author makes adjustments to the specimen dimensions. The design and fabrication of specimen will follow the ASTM E8/E8M standard.
Static tensile test is the most common destructive testing that provides information about the material’s mechanical properties such as Modulus of Elasticity, Yield Strength and Ultimate Tensile Strength. After the test is performed, raw data will be collected to plot the stress-strain curve. The results will be analysed and compared against past FYP findings. In addition, this report aims to serve as a future reference on Aluminum 6061-T6.
This project will focus on improving the experimental procedure to obtain accurate and consistent results. Lastly, this report aims to serve as future reference on Aluminum 6061-T6, and recommendations for static tensile tests will be discussed.Bachelor of Engineering (Mechanical Engineering
Stock-for-stock mergers : earnings management and the pooling-purchase choice. Do investors care?
No full textWe investigate whether there is a relationship between the level of aggression of an acquiring firm in managing earnings prior to the completion of a stock-for-stock merger and its choice of accounting method for the merger. Market reaction to the combination of earnings management and accounting method choice is also investigated
New pulse shapes for enhanced spectral efficiency in digital radio communications
No full textLinear modulation schemes such as phase shift keying (PSK) and quadrature amplitude modulation (QAM) are inherently spectrally efficient. This research seeks enhanced spectral efficiency by designing new spectrally efficient pulse shapes for such digital modulations. The pulses designed are of finite duration and exhibit zero intersymbol interference when received through an additive white Gaussian noise (AWGN) channel. It is shown that the resulting communications signals have optimal spectral roll-off while maintaining optimum bit error ratio performance when received via an AWGN channel. The bandwidths and power spectral densities of communications signals using these pulses are compared with traditional spectrally efficient communications signals.Approved for public release; distribution is unlimited.Singapore Defence Science and Technology Agency author (civilian).http://archive.org/details/newpulseshapesfo10945323
Transborder Industrialization and Singapore's 'Clones' in Indonesia, China and Vietnam: A Strategy Reconsidered
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