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Crafting chirality in three dimensions via a novel fabrication technique for bound states in the continuum metasurfaces

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Light(science & Applications) 2024年第3期13卷 390-392页

作者： Zaid Haddadin Anna My Nguyen Lisa V.Poulikakos Department of Electrical&Computer Engineering University of California San DiegoLa JollaCAUSA Department of Mechanical&Aerospace Engineering University of California San DiegoLa JollaCAUSA Program of Materials Science&Engineering University of California San DiegoLa JollaCAUSA

An additional deposition step was added to a multi-step electron beam lithographic fabrication process to unlock the height dimension as an accessible parameter for resonators comprising unit cells of quasi-bound stat... 详细信息

关键词： dimensions dimension intrinsic

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Fabrication of crack-free aluminum alloy 6061 parts using laser foil printing process

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Rapid Prototyping Journal 2024年第4期30卷 722-732页

作者： Wang, Yu-Xiang Hung, Chia-Hung Pommerenke, Hans Wu, Sung-Heng Liu, Tsai-Yun Department of Mechanical Engineering National Cheng Kung University Tainan Taiwan Department of Materials Science and Engineering Missouri University of Science and Technology RollaMO United States Department of Mechanical and Aerospace Engineering Missouri University of Science and Technology RollaMO United States Core Facility Center National Cheng Kung University Tainan Taiwan

Purpose: This paper aims to present the fabrication of 6061 aluminum alloy (AA6061) using a promising laser additive manufacturing process, called the laser-foil-printing (LFP) process. The process window of AA6061 in LFP was established to optimize process parameters for the fabrication of high strength, dense and crack-free parts even though AA6061 is challenging for laser additive manufacturing processes due to hot-cracking issues. Design/methodology/approach: The multilayers AA6061 parts were fabricated by LFP to characterize for cracks and porosity. mechanical properties of the LFP-fabricated AA6061 parts were tested using Vicker’s microhardness and tensile testes. The electron backscattered diffraction (EBSD) technique was used to reveal the grain structure and preferred orientation of AA6061 parts. Findings: The crack-free AA6061 parts with a high relative density of 99.8% were successfully fabricated using the optimal process parameters in LFP. The LFP-fabricated parts exhibited exceptional tensile strength and comparable ductility compared to AA6061 samples fabricated by conventional laser powder bed fusion (LPBF) processes. The EBSD result shows the formation of cracks was correlated with the cooling rate of the melt pool as cracks tended to develop within finer grain structures, which were formed in a shorter solidification time and higher cooling rate. Originality/value: This study presents the pioneering achievement of fabricating crack-free AA6061 parts using LFP without the necessity of preheating the substrate or mixing nanoparticles into the melt pool during the laser melting. The study includes a comprehensive examination of both the mechanical properties and grain structures, with comparisons made to parts produced through the traditional LPBF method. © 2024, Emerald Publishing Limited.

关键词： 3D printing

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Amorphous Iridium Oxide-Integrated Anode Electrodes with Ultrahigh Material Utilization for Hydrogen Production at Industrial Current Densities

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Nano-Micro Letters 2024年第10期16卷 225-239页

作者： Lei Ding Kui Li Weitian Wang Zhiqiang Xie Shule Yu Haoran Yu David ACullen Alex Keane Kathy Ayers Christopher BCapuano Fangyuan Liu Pu-Xian Gao Feng-Yuan Zhang Department of Mechanical Aerospace and Biomedical EngineeringUniversity of TennesseeKnoxvilleTN 37996USA Oak Ridge National Lab Center for Nanophase Materials SciencesOak RidgeTN 37831USA Nel Hydrogen WallingfordCT 06492USA Institute of Materials Science University of ConnecticutStorrsCT 06269USA Department of Materials Science and Engineering University of ConnecticutStorrsCT 06269USA

Herein,ionomer-free amorphous iridium oxide(IrO_(x))thin electrodes are first developed as highly active anodes for proton exchange membrane electrolyzer cells(PEMECs)via low-cost,environmentally friendly,and easily scalable electrodeposition at room *** with a Nafion 117 membrane,the IrO_(x)-integrated electrode with an ultralow loading of 0.075 mg cm^(-2)delivers a high cell efficiency of about 90%,achieving more than 96%catalyst savings and 42-fold higher catalyst utilization compared to commercial catalyst-coated membrane(2 mg cm^(-2)).Additionally,the IrO_(x)electrode demonstrates superior performance,higher catalyst utilization and significantly simplified fabrication with easy scalability compared with the most previously reported ***,the remarkable performance could be mainly due to the amorphous phase property,sufficient Ir^(3+)content,and rich surface hydroxide groups in ***,due to the high activity,high cell efficiency,an economical,greatly simplified and easily scalable fabrication process,and ultrahigh material utilization,the IrO_(x)electrode shows great potential to be applied in industry and accelerates the commercialization of PEMECs and renewable energy evolution.

关键词： Ionomer-free Amorphous IrOx electrodes Ultrahigh material utilization Scalable electrodeposition Hydrogen production

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Sensitivity study of resolution and convergence requirements for the extended overlap region in wall-bounded turbulence

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Physical Review Fluids 2024年第8期9卷 L082601-L082601页

作者： Sergio Hoyas Ricardo Vinuesa Peter Schmid Hassan Nagib Instituto Universitario de Matemática Pura y Aplicada Universitat Politècnica de València FLOW Engineering Mechanics KTH Royal Institute of Technology Department of Mechanical Engineering Division of Physical Sciences and Engineering (PSE) King Abdullah University of Science and Technology (KAUST) Mechanical Materials and Aerospace Engineering Armour College of Engineering ILLINOIS TECH

Direct numerical simulations (DNSs) are among the most powerful tools for studying turbulent flows. Even though the achievable Reynolds numbers are lower than those obtained through experimental means, DNS offers a clear advantage: The entire velocity field is known, allowing for the evaluation of any desired quantity. This capability includes the computation of derivatives of all relevant terms. One such derivative provides the indicator function, which is the product of the wall distance and the wall-normal derivative of the mean streamwise velocity. This derivative may depend on mesh spacing and distribution, but it is extremely affected by the convergence of the simulation. The indicator function is crucial for understanding inner and outer interactions in wall-bounded flows and describing the overlap region between them. We find a clear dependence of this indicator function on the mesh distributions we examine, raising questions about classical mesh and convergence requirements for DNS and achievable accuracy. Within the framework of the logarithmic plus linear overlap region, coupled with a parametric study of channel flows and some pipe flows, sensitivities of extracted overlap parameters are examined. This study reveals a path to establishing their high-Reτ or nearly asymptotic values at modest Reynolds numbers, but larger than the ones used in this work, accessible by high-quality DNS with reasonable cost.

关键词： Boundary layers Complex fluids Three-dimensional turbulence Turbulence Turbulent boundary layers

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Self-supported copper-based gas diffusion electrodes improve the local CO_(2)concentration for efficient electrochemical CO_(2)reduction

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Frontiers of Chemical science and engineering 2024年第3期18卷 51-62页

作者： Azeem Mustafa Bachirou Guene Lougou Yong Shuai Zhijiang Wang Haseeb-ur-Rehman Samia Razzaq Wei Wang Ruming Pan Jiupeng Zhao Key Laboratory of Aerospace Thermophysics of MIIT Harbin Institute of TechnologyHarbin150001China School of Energy Science and Engineering Harbin Institute of TechnologyHarbin150001China MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage School of Chemistry and Chemical EngineeringHarbin Institute of TechnologyHarbin150001China Mechanical Engineering Department University of Engineering and TechnologyTaxila47050Pakistan School of Aerospace Mechanical and Mechatronics EngineeringUniversity of SydneySydney2006Australia

Electrochemical CO_(2)reduction is a sustainable approach in green chemistry that enables the production of valuable chemicals and fuels while mitigating the environmental impact associated with CO_(2)*** its several advantages,this technology suffers from an intrinsically low CO_(2)solubility in aqueous solutions,resulting in a lower local CO_(2)concentration near the electrode,which yields lower current densities and restricts product *** diffusion electrodes(GDEs),particularly those with tubular architectures,can solve these issues by increasing the local CO_(2)concentration and triple-phase interface,providing abundant electroactive sites to achieve superior reaction *** this study,robust and self-supported Cu flow-through gas diffusion electrodes(FTGDEs)were synthesized for efficient formate production via electrochemical CO_(2)*** were further compared with traditional Cu electrodes,and it was found that higher local CO_(2)concentration due to improved mass transfer,the abundant surface area available for the generation of the triple-phase interface,and the porous structure of Cu FTGDEs enabled high formate Faradaic efficiency(76%)and current density(265 mA¸cm^(−2))at–0.9 V *** hydrogen electrode(RHE)in 0.5 mol·L^(−1)*** combined phase inversion and calcination process of the Cu FTGDEs helped maintain a stable operation for several *** catalytic performance of the Cu FTGDEs was further investigated in a non-gas diffusion configuration to demonstrate the impact of local gas concentration on the activity and performance of electrochemical CO_(2)*** study demonstrates the potential of flow-through gas-diffusion electrodes to enhance reaction kinetics for the highly efficient and selective reduction of CO_(2),offering promising applications in sustainable electrochemical processes.

关键词： CO_(2)electroreduction flow-through delivery hollow fiber structure local concentration formate

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Oscillatory Hall effect from magnetoelectronic coupling in flexoelectronic silicon

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Physical Review B 2024年第8期109卷 L081113-L081113页

作者： Paul C. Lou Ravindra G. Bhardwaj Anand Katailiha W. P. Beyermann Sandeep Kumar Department of Mechanical Engineering University of California Riverside California 92521 USA Department of Physics and Astronomy University of California Riverside California 92521 USA Materials Science and Engineering Program University of California Riverside California 92521 USA

Magnetoelectronic coupling can be defined as cross-domain coupling between electronic and magnetic properties, where modulation in magnetic properties changes the electronic properties. In this Letter, explicit experimental evidence of magnetoelectronic coupling is presented, which is uncovered from the oscillatory Hall effect response in Hall measurement. The strain gradient in a MgO (1.8 nm)/p-Si (∼400 nm) freestanding sample leads to transfer of electrons (∼5×1018cm−3) from valence to conduction band due to flexoelectronic charge separation in the p-Si layer. The resulting flexoelectronic polarization gives rise to the temporal magnetic moment from dynamical multiferroicity. The external magnetic field changes the net temporal magnetic moment, which causes modulations in charge carrier concentration and oscillatory Hall effect. The period of oscillatory Hall response is 1.12 T, which is attributed to the magnitude of the temporal magnetic moment. The discovery of the oscillatory Hall effect adds another member to the family of Hall effects.

关键词： Hall effect Doped semiconductors Electronically polarized systems Flexoelectrics Multiferroics Hall bar

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Microstructural evolution and its influence on the wear resistance of a laser directed energy deposited Ni-based single crystal superalloy

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材料科学技术（英文版） 2025年第2期205卷 127-138页

作者： Chenyu Ren Kai Chen Jingjing Liang R.Lakshmi Narayan Upadrasta Ramamurty Jinguo Li Center for Advancing Materials Performance from the Nanoscale(CAMP-Nano) State Key Laboratory for Mechanical Behavior of MaterialsXi'an Jiaotong UniversityXi'an 710049China Superalloys Division Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Department of Materials Science and Engineering Indian Institute of TechnologyDelhiNew Delhi 110016India School of Mechanical and Aerospace Engineering Nanyang Technological UniversitySingapore 639798Singapore

The wear behavior of Ni-based single crystal(NBSC)superalloy SRR99 fabricated by laser-directed energy deposition(LDED)is investigated and compared with that of its cast *** γ'precipitate size in the latter is＞400 nm,that in the former is an order of magnitude *** sliding wear tests reveal that the wear rate and coefficient of friction of the LDED alloy are 75％and 20％lower than that of its cast counterpart,*** transmission electron microscopy investigation of the wear-tested cast alloy indicates that there is orientation change and formation of nanoscale grains only at the top layer of the worn surface,whereas regions below undergo moderate plastic deformation via dislocation *** contrast,the sub-surface of the worn LDED alloy has a graded microstructure,with a composite of NiO/γ-Ni on the top,γ'free nano-grains in the middle,and a highly deformed nanoscale layer at the *** improved wear behavior of the LDED alloy is attributed to its higher dislocation density,finer γ'precipitates,and the formation of this graded ***,a detailed description of mechanisms that lead to the formation of this unique graded microstructure is provided.

关键词： In-situ formed gradient nanostructure Enhanced wear resistance Laser-directed energy deposition additive manufacturing Ni-based single crystal superalloys Plastic deformation

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Effect of Build and Scan Direction on Tensile Properties of Selective Laser Melted SS316L Alloy

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Lasers in Manufacturing and materials Processing 2023年第2期10卷 330-352页

作者： Kumar, B. Sai Bharat Yadav, Dhananjay K. Jain, Roopam Gupta, Nikhil Gurao, Nilesh P. Sinha, Niraj Department of Mechanical Engineering Indian Institute of Technology Kanpur208016 India Department of Materials Science and Engineering Indian Institute of Technology Kanpur208016 India Department of Mechanical and Aerospace Engineering New York University Tandon School of Engineering BrooklynNY11201 United States

Process-microstructure-mechanical property linkage was established for selective laser melted SS 316 stainless steel alloy by studying the role of scan direction and build direction on the tensile properties of the alloy with detailed microstructural characterization using electron backscatter diffraction. A wide range of mechanical properties comprising a range of ductility from 78 and 35% with a range of yield and ultimate strength of 275 to 313 MPa and 342 to 428 MPa, respectively, for the alloy, shows the capability of selective laser melting to cover a large property space. Similarly, a wide toughness range of 11,970 to 27,760 MJ/m3 is such that the sample with the scan direction perpendicular to the plane containing the tensile axis shows the highest toughness. The synergy of strengthening and strain hardening mechanisms like Taylor hardening, dislocation strengthening and twin induced plasticity to modulate the properties of SS316L alloy is established. Graphical Abstract: [Figure not available: see fulltext.]. © 2023, The Author(s), under exclusive licence to Springer science+Business Media, LLC, part of Springer Nature.

关键词： Strain hardening

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Recent advances of magnesium hydride as an energy storage material

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Journal of materials science & Technology 2023年第18期149卷 99-111页

作者： Mengchen Song Liuting Zhang Fuying Wu Haoyu Zhang Hu Zhao Lixin Chen Hong Li School of Energy and Power Instrumental Analysis CenterJiangsu University of Science and TechnologyZhenjiang 212003China School of Mechanical and Aerospace Engineering Nanyang Technological University639798Singapore State Key Laboratory of Silicon Materials Department of Materials Science and EngineeringZhejiang UniversityHangzhou 310027China

Energy storage is the key for large-scale application of renewable energy,however,massive efficient en-ergy storage is very *** hydride(MgH_(2))offers a wide range of potential applications as an energy carrier due to its advantages of low cost,abundant supplies,and high energy storage ***,the practical application of MgH_(2) for energy storage is still impeded by its sluggish kinetics,poor cycling stability,***,we provide an overview of recent advances of MgH_(2) for enhancing the hydrogen storage,lithium-ion storage,and heat storage *** hydrogen storage,a particular emphasis was put on altering the kinetics and thermodynamics of MgH_(2) via catalyzing,alloying,nano-sizing,and *** to MgH_(2) as a battery anode material mainly focus on the effect of additives,electrolytes,and structure *** heat storage apparatus was proposed based on MgH_(2) and coupled with other materials or systems to improve the heat storage and economic ***,prospects of MgH_(2) in these fields are *** review would stimulate more insightful and pioneering research for the design and preparation of MgH_(2) with excellent energy storage performances.

关键词： Magnesium hydride Energy storage Hydrogen storage Li-ion battery Heat storage

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Stress Distributions in Brazed Single-Lap Joints Under Tensile Loading (vol 54, pg 1116, 2023)

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METALLURGICAL AND materials TRANSACTIONS A-PHYSICAL METALLURGY AND materials science 2023年第8期54卷 3370-3370页

作者： Kemmenoe, D. J. Sibley School of Mechanical and Aerospace Engineering Cornell University Upson Hall Ithaca NY 14853 USA Department of Materials Science and Engineering Cornell University Bard Hall Ithaca NY 14853 USA

The most common method for characterizing the strength of brazed joints is uniaxial tension testing of single lap joints (SLJs). Standard interpretations depend on the assumption that the average shear stress at failure is the key metric in determining joint strength. However, it is evident from the geometry that the stress distributions must be inhomogeneous with shear lag type stress concentrations at the ends of the overlap regions. Eccentric loading causes overlap rotation and bending stresses that amplify the stress concentrations and result in geometric nonlinearity. Unfortunately, details of the distributions of normal and shear stresses on the braze needed to understand failure have not been presented. Thus, finite element analysis was used to quantify these stress distributions using 2D elastic and elasto-plastic models of monolithic stainless steel SLJs. Bending stresses and normal and shear stresses acting on the braze were determined over a wide range of overlap ratios and applied stresses. For all conditions, stresses are highly concentrated in a narrow region at overlap ends with peak normal stresses exceeding peak shear stresses. Variations in peak stresses with applied stress and overlap ratio were found to fully explain experimental joint strength data. Common interpretations based on the average shear stress at failure are found to be incorrect. Implications for testing, interpretation, and joint design are discussed.

关键词： Stress concentration

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