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Additive manufacturing of composite materials and functionally graded structures using selective heat melting technique

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Journal of Materials Science & Technology 2020年第12期47卷 243-252页

作者： Kalaimani Markandan Ruijing Lim Pawan Kumar Kanaujia Ian Seetoh Muhammad Raziq bin Mohd Rosdi Zhi Huey Tey Jun Seng Goh Yee Cheong Lam Changquan Lai Temasek Laboratories Nanyang Technological University50 Nanyang Drive637553Singapore school of Physical&Mathematical Sciences Nanyang Technological University21 Nanyang Link637371Singapore school of Mechanical&Aerospace Engineering Nanyang Technological University50 Nanyang Avenue639798Singapore school of Materials Science&Engineering Nanyang Technological University50 Nanyang Avenue639798Singapore

The feasibility of using selective heat melting(SHM) to fabricate composite materials and functionally graded structures was *** report,for the first time,the successful 3 D printing of copper(Cu)-polyethylene(PE) composite,iron(Fe)-polyethylene(PE) composite and functionally graded CuO foams using the SHM *** was found that a low feed rate,high airflow rate and high airflow temperature were required for efficient delivery of heat from the emitted hot air to the powder bed,so that the PE binder particles can melt and form dense composites with smooth *** best mechanical properties were exhibited by composites with 80 vol.% PE,as lower PE concentrations led to deficient binding of the metal particles,while higher PE concentrations meant that very few metal particles were available to strengthen the *** strength exhibited by Cu-PE composites was comparable to engineering plastics such as polycarbonate,with the added advantage of being electrically *** average conductivity of the samples,0.152±0.28 S/m,was on par with physically crosslinked graphene *** subjecting a Cu-PE composite,with Cu concentration graded from 10 vol.% to 30 vol.%,to a high temperature debinding and sintering treatment in air,CuO foam with graded porosity can be *** CuO foam was observed to fail in a layer-by-layer manner under mechanical compression,which is a characteristic of functionally graded *** study shows that,compared to existing 3 D printing techniques,SHM can be cheaper,have wider material compatibility,occupy a smaller footprint and potentially induce less residual stresses in the fabricated ***,it could be a valuable complement to current additive manufacturing techniques for fabricating mechanically strong composite materials and functionally graded structures.

关键词： Selective heat melting Functionally graded materials Additive manufacturing Multimaterial

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Understanding Discrepancy of Power System Dynamic Security Assessment with Unknown Faults: A Reliable Transfer Learning-based Method

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CSEE Journal of Power and Energy Systems 2024年第1期10卷 427-431页

作者： Chao Ren Han Yu Yan Xu Zhao Yang Dong school of Computer Science and Engineering Nanyang Technological UniversitySingapore school of Electrical and Electronic Engineering Nanyang Technological UniversitySingapore

This letter proposes a reliable transfer learning(RTL)method for pre-fault dynamic security assessment(DSA)in power systems to improve DSA performance in the presence of potentially related unknown *** takes individual discrepancies into consideration and can handle unknown faults with incomplete *** experiment results demonstrate high DSA accuracy and computational efficiency of the proposed RTL *** analysis shows RTL can guarantee system performance.

关键词： Adversarial training dynamic security assessment maximum classifier discrepancy missing data transfer learning

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A machine learning approach to map crystal orientation by optical microscopy

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npj Computational Materials 2022年第1期8卷 70-78页

作者： Mallory Wittwer Matteo Seita school of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingaporeSingapore school of Materials Science and Engineering Nanyang Technological UniversitySingaporeSingapore

Mapping grain orientation in crystalline solids is essential to investigate the relationships between local microstructure and crystallography and interpret materials *** of the main techniques used to perform these studies is electron backscatter diffraction(EBSD).Due to the limited measurement throughput,however,EBSD is not suitable for characterizing samples with long-range microstructure heterogeneity,nor for building large material libraries that include numerous *** present a machine learning approach for high-throughput crystal orientation mapping,which relies on the optical technique called directional reflectance *** successfully apply our method on Inconel 718 specimens produced by additive manufacturing,which exhibit complex,spatially-varying *** results demonstrate that optical orientation mapping on a metal alloy is *** our method is data-driven,it can be easily extended to different alloy systems produced using different manufacturing processes.

关键词： alloy microstructure crystal

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Time-varying formation tracking for uncertain second-order nonlinear multi-agent systems

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Frontiers of Information Technology & Electronic Engineering 2019年第1期20卷 76-87页

作者： Mao-peng RAN Li-hua XIE Jun-cheng LI school of Electrical and Electronic Engineering Nanyang Technological University

Our study is concerned with the time-varying formation tracking problem for second-order multi-agent systems that are subject to unknown nonlinear dynamics and external disturbance, and the states of the followers form a predefined time-varying formation while tracking the state of the leader. The total uncertainty lumps the unknown nonlinear dynamics and the external disturbance, and is regarded as an extended state of the agent. To estimate the total uncertainty, we design an extended state observer(ESO). Then we propose a novel ESO based time-varying formation tracking protocol. It is proved that, under the proposed protocol, the ESO estimation error and the time-varying formation tracking error can be made arbitrarily small. An application to the target enclosing problem for multiple unmanned aerial vehicles(UAVs) verifies the effectiveness and superiority of the proposed approach.

关键词： Multi-agent system Time-varying formation Formation tracking Nonlinear dynamics Extended state observer(ESO)

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Lipid-polymer hybrid nanoparticles with rhamnolipid-triggered release capabilities as anti-biofilm drug delivery vehicles

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Particuology 2012年第3期10卷 327-333页

作者： Wean Sin Cheow Kunn Hadinoto school of Chemical and Biomedical Engineering Nanyang Technological University

In lung biofilm infection therapies, the use of lipid-polymer hybrid nanoparticles to encapsulate drugs has emerged as a promising alternative to using liposomes because they have superior physicochemical stability and still possess the biofilm affinity and sputum-penetrating ability ofliposomes. To be deemed equally efficacious as liposomes against bacterial biofilms, however, the capability of hybrid nanoparticles to target-release encapsulated drugs at biofilm colonies must be demonstrated. This communication details our investigations into the trigger-release characteristics of hybrid nanoparticles in response to encountering rhamnolipids, which are ubiquitously present in biofilm colonies of Pseudomonas aeruginosa, a major respiratory pathogen. Poly（lactic-co-glycolic acid） and phospbatidylcholine were used as the poly- mer nanoparticle core and lipid coat, respectively. These investigations were performed using compounds from various biopharmaceutical classification systems （BCS） that differ in their lipid-membrane permeabilities. The release of BCS Class II1 compounds, which have poor lipid-membrane permeabilities, was successfully triggered by rhamnolipids at a concentration approximately equal to their clinically observed value, and this release was attributed to the disruption of lipid coats by rhamnolipid micelles. Not unexpectedly, BCS Class I compounds, which have high lipid-membrane permeabilities, were released freely whether or not rhamnolipids were present. The rate of the triggered release can be controlled by incor- porating an additional lipid layer on the hybrid nanoparticles via the electrostatically driven adsorption of lipid vesicles.

关键词： Hybrid nanoparticlesLiposomesBiofilmPseudomonas aeruginosaTriggered releaseRhamnolipidCalcein

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Frequency equations of nonlocal elastic micro/nanobeams with the consideration of the surface effects

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Applied Mathematics and Mechanics(English Edition) 2018年第8期39卷 1089-1102页

作者： H.S.ZHAO Y.ZHANG S.T.LIE school of Civil and Environmental Engineering Nanyang Technological University

A nonlocal elastic micro/nanobeam is theoretically modeled with the consideration of the surface elasticity, the residual surface stress, and the rotatory inertia,in which the nonlocal and surface effects are considered. Three types of boundary conditions, i.e., hinged-hinged, clamped-clamped, and clamped-hinged ends, are examined. For a hinged-hinged beam, an exact and explicit natural frequency equation is derived based on the established mathematical model. The Fredholm integral equation is adopted to deduce the approximate fundamental frequency equations for the clamped-clamped and clamped-hinged beams. In sum, the explicit frequency equations for the micro/nanobeam under three types of boundary conditions are proposed to reveal the dependence of the natural frequency on the effects of the nonlocal elasticity, the surface elasticity, the residual surface stress, and the rotatory inertia, providing a more convenient means in comparison with numerical computations.

关键词： Fredholm integral equation micro/nanobeam natural frequency nonlocal elasticity surface effect

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In-line digital holography for dynamic metrology of MEMS(Invited Paper)

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Chinese Optics Letters 2009年第12期7卷 1117-1122页

作者： Vijay Raj Singh Anand Asundi school of Mechanical and Aerospace Engineering Nanyang Technological University

In-line digital holography helps to relax the spatial resolution requirement on charge-coupled device sensors for digital recording of holograms and to utilize the full sensing area for image reconstruction which provides larger field of view and better imaging resolution. In this letter, a lensless in-line digital holographic microscopy is presented for dynamic metrology of micro-electro-mechanical system devices. The methodologies of interferometry and time-averaged in-line digital holography are presented for dynamic measurements, which are also useful for simultaneous suppression of in-line waves from real image wave. The experimental results are presented for dynamic thermal characterization of microheater and vibration analysis of cantilevers.

关键词： line MEMS

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Explicit frequency equations of free vibration of a nonlocal Timoshenko beam with surface effects

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Acta Mechanica Sinica 2018年第4期34卷 676-688页

作者： Hai-Sheng Zhao Yao Zhang Seng-Tjhen Lie school of Civil and Environmental Engineering Nanyang Technological University

Considerations of nonlocal elasticity and surface effects in micro-and nanoscale beams are both important for the accurate prediction of natural frequency. In this study, the governing equation of a nonlocal Timoshenko beam with surface effects is established by taking into account three types of boundary conditions： hinged–hinged, clamped–clamped and clamped–hinged ends. For a hinged–hinged beam, an exact and explicit natural frequency equation is obtained. However, for clamped–clamped and clamped–hinged beams, the solutions of corresponding frequency equations must be determined numerically due to their transcendental nature. Hence, the Fredholm integral equation approach coupled with a curve fitting method is employed to derive the approximate fundamental frequency equations, which can predict the frequency values with high accuracy. In short,explicit frequency equations of the Timoshenko beam for three types of boundary conditions are proposed to exhibit directly the dependence of the natural frequency on the nonlocal elasticity, surface elasticity, residual surface stress, shear deformation and rotatory inertia, avoiding the complicated numerical computation.

关键词： Fredholm integral equation Natural frequency Nonlocal elasticity Surface effects Timoshenko beam

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Rules essential for water molecular undercoordination

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Chinese Physics B 2020年第8期29卷 33-47页

作者： Chang Q Sun school of EEE Nanyang Technological UniversitySingapore 639798

A sequential of concepts developed in the last decade has enabled a resolution to multiple anomalies of water ice and its low-dimensionality,*** concepts include the coupled hydrogen bond(O:H–O)oscillator pair,segmental specific heat,three-body coupling potentials,quasisolidity,and *** anomalies include ice buoyancy,ice slipperiness,water skin toughness,supercooling and superheating at the nanoscale,*** shows consistently that molecular undercoordination shortens the H–O bond and stiffens its phonon while undercoordination does the O:H nonbond contrastingly associated with strong lone pair“:”polarization,which endows the low-dimensional water ice with *** supersolid phase is hydrophobic,less dense,viscoelastic,thermally more diffusive,and stable,having longer electron and phonon *** equal number of lone pairs and protons reserves the configuration and orientation of the coupled O:H–O bonds and restricts molecular rotation and proton hopping,which entitles water the simplest,ordered,tetrahedrally-coordinated,fluctuating molecular crystal covered with a supersolid *** O:H–O segmental cooperativity and specific-heat disparity form the soul dictate the extraordinary adaptivity,reactivity,recoverability,and sensitivity of water ice when subjecting to physical *** is recommended that the premise of“hydrogen bonding and electronic dynamics”would deepen the insight into the core physics and chemistry of water ice.

关键词： hydrogen bonding molecular crystals structural transitions in nanoscale materials liquid-liquid transitions

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Pilot studies on two dimensional wave propagation in rock masses

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中国有色金属学会会刊：英文版 2005年第4期15卷 949-955页

作者：雷卫东 M.H.Ashraf 赵坚 school of Civil and Environmental Engineering Nanyang Technological University

Pilot studies on two dimensional(2-D) wave propagation through single joint or multiple parallel joints were comprehensively conducted, using a suitable data processing method. The possible factors influencing the transmission ratio in 2-D wave propagation under certain circumstances in rock masses were studied. It is found that in the process of 2-D wave propagation, for any radial line, the amount, the stiffness and the spacing of the joints influence the transmission ratio; by contrast, the transmission ratio at any point is independent of the radial distance from the center of wave source. It is also found that the transmission ratio for every grid-point along a single circle can present the transmission ratio for every grid-point after a certain quantity of joints. For the special radian direction(normal to the joints), it is concluded that the transmission ratio is dominated by the normal stiffness; while the influence of shear stiffness is negligible. The radius of the tunnel or borehole for the source wave does not affect the transmission ratio in 2-D wave propagation.

关键词：矿山岩石力学引航理论二维波传播

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