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Soil-structure interaction on shallow rigid circular foundation:plane SH waves from far-field earthquakes

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Earthquake Engineering and Engineering Vibration 2014年第1期13卷 29-45页

作者： Vincent W.lee hao Luo Civil & Environmental Engineering Univ. of Southern California HNTB Corporation

A closed-form wave function analytic solution of two-dimensional scattering and diffraction of incident plane SH-waves by a fl exible wall on a rigid shallow circular foundation embedded in an elastic half-space is presented. This research generalizes the previous solution by Trifunac in 1972, which tackled only the semi-circular foundation, to arbitrary shallow circular-arc foundation cases, and is thus comparatively more realistic. Ground surface displacement spectra at higher frequencies are also obtained. As an analytical series solution, the accuracy and error analysis of the numerical results are also discussed. It was observed from the results that the rise-to-span ratio of the foundation profi le, frequency of incident waves, and mass ratios of different media(foundation-structure-soil) are the three primary factors that may affect the surface ground motion amplitudes near the structure.

关键词： SH waves plane wave soil-structure interaction closed-form analytic solution Fourier-Bessel series

Mechanochemical effect on the microstructure and mechanical properties in ultraprecision machining of AA6061 alloy

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Journal of Materials Science & Technology 2021年第10期69卷 228-238页

作者： Jiayi Zhang Yan Jin lee hao Wang Department of Mechanical Engineering Faculty of EngineeringNational University of Singapore9 Engineering Drive 1Singapore 117575Singapore

The mechanochemical effect on the microcutting of AA6061 alloy is studied through characterization on the microgroove *** is a reduction in cutting and thrust forces with the application of ink during ***,the microhardness of the ink-affected microgroove is lower than that of the ink-free *** substructured grains exist in the ink-affected microgroove zone whilst deformed grains dominate in the ink-free microgroove zone produced by ***,the mechanochemical effect can facilitate the nucleation of precipitates in the microgroove zone and induce the formation of subgrains with multiple *** to the analysis and calculation,the main texture components of the ink-affected sample are Goss{110}and R{124},and that of the ink-free sample are Brass{110},Copper{112}and S{123}.Besides,a clear difference of slip systems is found between the ink-free and ink-affected microgrooves,and the results show that R texture is easier to form on the ink-affected microgroove.

关键词： Mechanochemical effect Microhardness Texture Nucleation Microcutting

The onset of surface-enhanced Raman scattering for single-particle detection of submicroplastics

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Journal of Environmental Sciences 2022年第11期34卷 58-64页

作者： Cheng-hao lee James Kar-Hei Fang Department of Applied Biology and Chemical Technology The Hong Kong Polytechnic UniversityKowloonHong Kong SARChina Institute of Textiles and Clothing The Hong Kong Polytechnic UniversityKowloonHong Kong SARChina Research Institute for Future Food The Hong Kong Polytechnic UniversityKowloonHong Kong SARChina State Key Laboratory of Marine Pollution City University of Hong KongKowloonHong Kong SARChina

Microplastics represent an emerging environmental problem worldwide, raising ecological and food safety concerns. Compared to microplastics, there is growing evidence of an even higher abundance of submicro-and nanoplastics in the environment, but a reliable monitoring method for detecting these smaller-sized plastics is lacking. Herein we presented the application of surface-enhanced Raman scattering(SERS) for this purpose. Particles of polystyrene(PS;600 nm) were used as the probe analyte. Gold nanourchins(Au NU;50 nm),i.e. urchin-shaped nanoparticles with irregular spikes around the core, were used as the SERS-active substrate. The effectiveness of SERS on PS was evaluated at a single-particle level with different numbers of Au NU in order to determine the minimum conditions required for the onset of the SERS effect. Our findings suggest that SERS of a single particle of PS can be induced by as few as 1–5 particles of Au NU, and that the use of excitation wavelength at 785 nm is appropriate to meet the red-shifted surface plasmon resonance of Au NU upon aggregation. These specifications provide additional information for the development of SERS-based tools for detecting plastic particles < 1 μm in food and environmental samples.

关键词： Microplastics Nanoplastics Gold nanourchins SERS Food contamination

Microstructure evaluation of shear bands of microcutting chips in AA6061 alloy under the mechanochemical effect

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Journal of Materials Science & Technology 2021年第32期91卷 178-186页

作者： Jiayi Zhang Yan Jin lee hao Wang Department of Mechanical Engineering Faculty of EngineeringNational University of Singapore9 Engineering Drive 1Singapore 117575Singapore

The mechanochemical effect on the microcutting of AA6061 alloy is studied through characterization on the chip. A pronounced reduction of machining forces and chip thickness was observed with mechanochemical effect during microcutting. Furthermore, electron backscattered diffraction(EBSD) and transmission electron microscopy(TEM) observations were performed on the chips and shear bands. The result reveals much coarser grains(24.6 μm in size) in the surfactant-affected chip than that in the surfactant-free chip(13.5 μm). Different grain orientations are induced by microcutting. {100} and{110} grain orientations are majority for surfactant-free chip, and {110} and {100}dominate most for all grain orientations for surfactant-affected chip. Additionally, since less localized shear strain and lower temperature are generated inside the shear band with mechanochemical effect,almost no recrystallization phenomena can be observed in this region. TEM analysis shows that fewer subgrains and dislocations could be observed inside the shear band of the surfactant-affected chip in comparison with the surfactant-free chip. Based on the high-resolution transmission electron microscopic(HRTEM) observations, dislocations were observed at the atomic scale. The results show that the main dislocation motion mode in shear bands of surfactant-free and surfactant-affected chips are dislocation climb and dislocation glide, respectively.

关键词： Mechanochemical effect Microcutting Shear band Chip formation Dislocation

Magneto-plasticity in micro-cutting of single-crystal copper

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Journal of Materials Science & Technology 2022年第29期124卷 121-134页

作者： Yunfa Guo YanJin lee Yu Zhang hao Wang Department of Mechanical Engineering National University of Singapore9 Engineering Drive 1Singapore 117575Singapore

The plasticity of metals can be significantly affected by the application of a magnetic field,otherwise known as the magneto-plastic *** paper investigates the magneto-plastic effect in the microcutting of a non-magnetic ductile material,single-crystal copper,under a weak magnetic field and reports the influence of the phenomenon on the cutting forces and machined surface quality.A softening effect was observed from the large reduction in cutting forces from 3.2 N to 1.5 N under the magnetic *** compared to the magnetic field intensity and polarity,the variation in magnetic field orientations with respect to the cutting direction exhibited a stronger influence on the cutting force,chip morphology,machined surface texture,subsurface microstructure,surface roughness,and machined surface microhardness of the copper *** analytical model was developed based on the geometry of the cutting chips to correlate the orientation-dependent influence of the magnetic field on the cutting *** the surface quality,excessive folds with four different types of morphology produced under magnetic-free cutting were suppressed after applying the magnetic field with the most significant improvement achieved with the 90°magnetic field *** magnetic-assisted changes in machined surface morphology also led to the reduction in machined surface roughness and *** optimistic micro-cutting outcomes in this work establish a greater understanding of the magneto-plastic effect and demonstrate the applicability of magneto-plasticity in ultraprecision manufacturing.

关键词： Micro-cutting Magnetic field Plasticity Mechanical response Anisotropy

Anti-plane (SH) waves diffraction by an underground semi-circular cavity:analytical solution

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Earthquake Engineering and Engineering Vibration 2010年第3期9卷 385-396页

作者： Luo hao Vincent W. lee Liang Jianwen HNTB Corporation Santa Ana CA 92707-8797 USA Sonny Astani Department of Civil and Environmental Engineering University of Southern California Los Angeles CA 90089-2531 USA Department of Civil Engineering Tianjin University Tianjin 300072 China

Diffraction of a two-dimensional （2D） semi-circular cavity in a half-space under incident SH-waves is studied using the classic wave function expansion method with a new de-coupling technique. This so-called ＂improved cosine half- range expansion＂ algorithm exhibits an excellent performance in reducing displacement residual errors at two rim points of concern. The governing equations are developed in a manner that minimizes the residues of the boundary conditions. Detailed derivation and analysis procedures as well as truncation of infinite linear governing equations are presented. The semi-circular cavity model presented in this paper, due to its simple profile, is expected to be used in seismic wave propagation studies as a benchmark for examining the accuracies of various analytical or numerical methods for mixed-boundary wave propagation problems.

关键词： plane SH waves diffraction, semi-circular cavity half-space improved cosine half-range expansion

Mesoplasticity Approach to Studies of the Cutting Mechanism in Ultra-precision Machining

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Chinese Journal of Mechanical Engineering 2014年第2期27卷 219-228页

作者： lee WB Rongbin WANG hao TO Suet CHEUNG Chi Fai CHAN Chang Yuen Partner State Key Laboratory of Ultra-precision Machining Technology The Hong Kong Polytechnic University

There have been various theoretical attempts by researchers worldwide to link up different scales of plasticity studies from the nano-, micro- and macro-scale of observation, based on molecular dynamics, crystal plasticity and continuum mechanics. Very few attempts, however, have been reported in ultra-precision machining studies. A mesoplasticity approach advocated by lee and Yang is adopted by the authors and is successfully applied to studies of the micro-cutting mechanisms in ultra-precision machining. Traditionally, the shear angle in metal cutting, as well as the cutting force variation, can only be determined from cutting tests. In the pioneering work of the authors, the use of mesoplasticity theory enables prediction of the fluctuation of the shear angle and micro-cutting force, shear band formation, chip morphology in diamond turning and size effect in nano-indentation. These findings are verified by experiments. The mesoplasticity formulation opens up a new direction of studies to enable how the plastic behaviour of materials and their constitutive representations in deformation processing, such as machining can be predicted, assessed and deduced from the basic properties of the materials measurable at the microscale.

关键词： ultra-precision machining cutting mechanism mesoplasticity shear angle prediction size effect,micro-cutting force variation high frequency tool-tip vibration

Effect of a weak magnetic field on ductile-brittle transition in micro-cutting of single-crystal calcium fluoride

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Journal of Materials Science & Technology 2022年第17期112卷 96-113页

作者： Yunfa Guo Yan Jin lee Yu Zhang Anastassia Sorkin Sergei Manzhos hao Wang Department of Mechanical Engineering National University of Singapore9 Engineering Drive 1Singapore 117575Singapore School of Materials and Chemical Technology Tokyo Institute of TechnologyOokayama 2-12-1Meguro-kuTokyo 152-8552Japan

Magneto-plasticity occurs when a weak magnetic field alters material plasticity and offers a viable solution to enhance ductile-mode cutting of brittle *** study demonstrates the susceptibility of non-magnetic single-crystal calcium fluoride(CaF_(2))to the magneto-plastic *** influence of magneto-plasticity on CaF_(2) was confirmed in micro-deformation tests under a weak magnetic field of 20 *** surface pile-up effect was weakened by 10-15 nm along with an enlarged plastic zone and suppressed crack propagation under the influence of the magnetic ***-cutting tests along different crystal orientations on the(111)plane of CaF_(2) revealed an increase in the ductile-brittle transition of the machined surface with the aid of magneto-plasticity where the largest increase in ductile-brittle transition occurred along the[112]orientation from 512 nm to a range of 664-806 ***,the subsurface damage layer was concurrently thinner under magnetic *** anisotropic influence of the magnetic field relative to the single-crystal orientation and the cutting direction was also *** analytical model was derived to determine an orientation factor M that successfully describes the anisotropy while considering the single-crystal dislocation behaviour,material fracture toughness,and the orientation of the magnetic *** suggested theoretical mechanism of magneto-plasticity via formation of non-singlet electronic states in defected configurations was confirmed with density functional theory *** successful findings on the influence of a weak magnetic field on plasticity present an opportunity for the adoption of magnetic-assisted micro-cutting of non-magnetic materials.

关键词： Magneto-plasticity Weak magnetic field Brittle material Ductile-brittle transition Micro-cutting

Theoretical elucidation of rare earth extraction and separation by diglycolamides from crystal structures and DFT simulations

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Journal of Rare Earths 2021年第7期39卷 858-865,I0004页

作者： Xiujing Peng Jianhui Su hao Li Yu Cui Jin Yong lee Guoxin Sun Institute for Smart Materials&Engineering School of Chemistry and Chemical EngineeringUniversity of JinanJinan 250022China Department of Chemistry Sungkyunkwan UniversitySuwon 16419Republic of Korea

Diglycolamides(DGAs) show excellent application prospects for the extraction and separation of rare earth metals from highly radioactive liquid wastes and rare earth *** extraction ability of DGAs for rare earth ions in nitrate or chloride media increases with increasing atomic number of the rare earth *** understand the origin of this phenomenon,three binuclear crystals [Ln(TEDGA)_(3)][Ln(NO_(3))_(6)] of N,N,N’,N’-tetraethyldiglycolamide(TEDGA) with rare earth ions La(Ⅲ),Pr(Ⅲ) and Eu(III) were prepared and characterized *** three complexes belong to the triclinic crystal system,P-1 space *** bond lengths of Ln-O_(amide) are significantly shorter than those of Ln-O_(ether) in the same *** Ln-O_(amide) and Ln-O_(enher) bond lengths gradually decrease with increasing atomic number of the rare earth *** dihedral angle formed by TEDGA and metal ions through the tridentate coordination gradually increases with increasing metal ion atomic number,tending toward the formation of sizeable planar coordination structures for the most massive rare earth *** structures of the compounds formed by the extractant and metal ion were optimized by means of DFT *** find that the interaction between TEDGA and the rare earth ion is dominated by electrostatic interaction by analyzing binding energy,WBIs,Mulliken charge,natural electron configurations,and molecular orbital *** covalent component of the Ln-O bonds of the complexes increases with increasing metal atomic *** observed increase in extraction and separation capacity of diglycolamides for rare earth ions with increasing atomic number might be due to the formation of two fivemember rings by one tridentate *** rare earth ions with large atomic numbers tend to form planar structures with large dihedral angles with DGA ligands.

关键词： Diglycolamide Extraction Separation Rare earth Crystal structures DFT simulations