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Optical coherence elastography of 3D bilayer soft solids using full-field and partial displacement measurements

Medicine in Novel Technology and Devices 2022年第3期15卷 55-64页

作者： Dongmei Zhao Haosen Wang Jianwei Deng Iryna Slavashevich Xu Guo Yue Mei Cuiru Sun State Key Laboratory of Structural Analysis for Industrial Equipment Department of Engineering MechanicsDalian University of TechnologyDalian 116023PR China International Research Center for Computational Mechanics Dalian University of TechnologyPR China Ningbo Institute of Dalian University of Technology NingboChina DUT-BSU Joint Institute Dalian University of Technology116023PR China department of Mechanics Tianjin University300354PR China Bio and nanomechanics department Belarusian State University220030MinskBelarus State Key Laboratory of Structural Analysis for Industrial Equipment Department of Engineering MechanicsDalian University of Tech-nologyDalian116023PR China

Characterizing nonhomogeneous elastic property distribution of soft tissues plays a crucial role in disease diagnosis and treatment.In this paper,we will apply the optical coherence elastography to reconstruct the shear modulus elastic property distribution of a bilayer solid.In the computational aspect,we adopt a well-established inverse technique that solves for every nodal shear modulus in the problem domain(NO method).Additionally,we also propose a novel inverse method that assumes the shear moduli merely vary along the thickness of the bilayer solid(TO method).The inversion tests using simulated data demonstrate that TO method performs better in reconstructing the shear modulus distribution.Further,we utilize the experimental data obtained from the optical coherence tomography to reconstruct the shear modulus distribution of a bilayer phantom.We observe that the quality of the reconstructed shear modulus distribution obtained by the partial displacement measurement is better than that obtained by the full-field displacement measurement.Particularly,merely using the displacement component along the loading direction significantly improves the reconstructed results.This work is of great significance in applying optical coherence elastography(OCE)to characterize the elastic property distribution of layered soft tissues such as skins and corneas.

关键词： Inverse problem Bilayer solid Shear modulus distribution Optical coherence elastography(OCE)

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Nonlinear stochastic dynamics of an array of coupled micromechanical oscillators

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International Journal of Mechanical System Dynamics 2023年第1期3卷 3-11页

作者： Maria I.Katsidoniotaki Ioannis Petromichelakis Ioannis A.Kougioumtzoglou department of Civil Engineering and Engineering Mechanics Columbia UniversityNew YorkNew YorkUSA

The stochastic response of a multi‐degree‐of‐freedom nonlinear dynamical system is determined based on the recently developed Wiener path integral(WPI)technique.The system can be construed as a representative model of electrostatically coupled arrays of micromechanical oscillators,and relates to an experiment performed by Buks and Roukes.Compared to alternative modeling and solution treatments in the literature,the paper exhibits the following novelties.First,typically adopted linear,or higher‐order polynomial,approximations of the nonlinear electrostatic forces are circumvented.Second,for the first time,stochastic modeling is employed by considering a random excitation component representing the effect of diverse noise sources on the system dynamics.Third,the resulting high‐dimensional,nonlinear system of coupled stochastic differential equations governing the dynamics of the micromechanical array is solved based on the WPI technique for determining the response joint probability density function.Comparisons with pertinent Monte Carlo simulation data demonstrate a quite high degree of accuracy and computational efficiency exhibited by the WPI technique.Further,it is shown that the proposed model can capture,at least in a qualitative manner,the salient aspects of the frequency domain response of the associated experimental setup.

关键词： Wiener path integral nonlinear system stochastic dynamics nanomechanics

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A comparative study on microstructure,nanomechanical and corrosion behaviors of AlCoCuFeNi high entropy alloys fabricated by selective laser melting and laser metal deposition

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Journal of Materials Science & Technology 2022年第36期131卷 221-230页

作者： Yaojia Ren Hong Wu Bin Liu Yong Liu Sheng Guo ZBJiao Ian Baker State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China department of Industrial and Materials Science Chalmers University of TechnologyGothenburg SE-41296Sweden department of Mechanical Engineering The Hong Kong Polytechnic UniversityHong Kong 999077China Thayer School of Engineering Dartmouth CollegeHanover NH 03755-8000United States

The present study investigated the microstructure,nanomechanics,and corrosion behavior of AlCoCuFeNi high entropy alloys fabricated by selective laser melting(SLM)and laser metal deposition(LMD).The microstructure of SLM-processed specimens was mainly composed of columnar-grained BCC matrix(^90μm in width)and Cu-rich twinned FCC phase.The columnar grains grew epitaxially along the building direction and exhibited a strong{001}texture.In comparison,a coarse columnar-grained BCC matrix(^150μm in width)with a strongertexture,rod-like B2 precipitates,and large core-shell structured FCC phases were formed in the LMD-processed specimens due to the higher heat accumulation effect.Consequently,the LMD-processed specimens showed a lower hardness,wear resistance,and corrosion resistance,but higher creep resistance and reduced Young's modulus than the SLM-processed specimens.Hot cracks occurred in both types of specimens,which could not be completely suppressed due to Cu segregation.

关键词： Selective laser melting Laser metal deposition High entropy alloys nanomechanics Corrosion

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Small scale effects on buckling and postbuckling behaviors of axially loaded FGM nanoshells based on nonlocal strain gradient elasticity theory

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Applied Mathematics and Mechanics(English Edition) 2018年第4期39卷 561-580页

作者： S.SAHMANI A.M.FATTAHI department of Mechanical Engineering Bandar Anzali Branch Islamic Azad University department of Mechanical Engineering Tabriz Branch Islamic Azad University

By means of a comprehensive theory of elasticity, namely, a nonlocal strain gradient continuum theory, size-dependent nonlinear axial instability characteristics of cylindrical nanoshells made of functionally graded material(FGM) are examined. To take small scale effects into consideration in a more accurate way, a nonlocal stress field parameter and an internal length scale parameter are incorporated simultaneously into an exponential shear deformation shell theory. The variation of material properties associated with FGM nanoshells is supposed along the shell thickness, and it is modeled based on the Mori-Tanaka homogenization scheme. With a boundary layer theory of shell buckling and a perturbation-based solving process, the nonlocal strain gradient load-deflection and load-shortening stability paths are derived explicitly. It is observed that the strain gradient size effect causes to the increases of both the critical axial buckling load and the width of snap-through phenomenon related to the postbuckling regime, while the nonlocal size dependency leads to the decreases of them. Moreover, the influence of the nonlocal type of small scale effect on the axial instability characteristics of FGM nanoshells is more than that of the strain gradient one.

关键词： nanomechanics functionally graded material(FGM) nonlocal strain gradient theory nonlinear instability perturbation technique

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NANO-MOIRE METHOD

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Acta Mechanica Sinica 1999年第3期15卷 283-288页

作者：戴福隆邢永明 department of Engineering Mechanics Tsinghua UniversityBeijing 100084China

Nano-moiré method presented in this paper is an experimental technique which allows direct measurement of nanoscopic mechanical parameters, such as displacement, strain and dislocation distribution. The basic idea is the formation of moiré fringes when a HREM (high resolution electron microscopy) image of crystal material is superimposed with a unidirectional grating. Fourier filtering technique is used to increase the contrast of fringes and to multiple the fringes. This method has atom-size sensitivity and spatial resolution, and relatively large range. It provides a new experimental technique with very high sensitivity and spatial resolution for nanomechanics.

关键词： Nano-moiré crystal lattice nano-deformation experimental moiré

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On the truth of nanoscale for nanobeams based on nonlocal elastic stress field theory:equilibrium,governing equation and static deflection

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Applied Mathematics and Mechanics(English Edition) 2010年第1期31卷 37-54页

作者： C. W. LIM department of Building and Construction City University of Hong Kong

This paper has successfully addressed three critical but overlooked issues in nonlocal elastic stress field theory for nanobeams：（i） why does the presence of increasing nonlocal effects induce reduced nanostructural stiffness in many, but not consistently for all, cases of study, i.e., increasing static deflection, decreasing natural frequency and decreasing buckling load, although physical intuition according to the nonlocal elasticity field theory first established by Eringen tells otherwise？（ii） the intriguing conclusion that nanoscale effects are missing in the solutions in many exemplary cases of study, e.g., bending deflection of a cantilever nanobeam with a point load at its tip; and （iii） the non-existence of additional higher-order boundary conditions for a higher-order governing differential equation. Applying the nonlocal elasticity field theory in nanomechanics and an exact variational principal approach, we derive the new equilibrium conditions, do- main governing differential equation and boundary conditions for bending of nanobeams. These equations and conditions involve essential higher-order differential terms which are opposite in sign with respect to the previously studies in the statics and dynamics of nonlocal nano-structures. The difference in higher-order terms results in reverse trends of nanoscale effects with respect to the conclusion of this paper. Effectively, this paper reports new equilibrium conditions, governing differential equation and boundary condi- tions and the true basic static responses for bending of nanobeams. It is also concluded that the widely accepted equilibrium conditions of nonlocal nanostructures are in fact not in equilibrium, but they can be made perfect should the nonlocal bending moment be replaced by an effective nonlocal bending moment. These conclusions are substantiated, in a general sense, by other approaches in nanostructural models such as strain gradient theory, modified couple stress models and experiments.

关键词： bending effective nonlocal bending moment nanobeam nanomechanics,nanoscale nonlocal elastic stress strain gradient

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DE膜在电场和预拉伸作用下的褶皱机理研究

DE膜在电场和预拉伸作用下的褶皱机理研究

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2018年全国固体力学学术会议

作者：税朗泉刘益伦陈曦武汉大学土木建筑工程学院西安交通大学航天航空学院 Columbia nanomechanics Research Center Department of Earth and Environmental EngineeringColumbia University

介电弹性体是构建新一代柔性驱动器的核心材料,介电弹性薄膜的力学稳定是其作为驱动器的前提,除了力学的破坏、电击穿和力电失稳,屈曲/褶皱也是其稳定性研究的重要内容。本文基于超弹性本构和薄膜非线性大变形理论研究了介电弹性薄膜的... 详细信息

介电弹性体是构建新一代柔性驱动器的核心材料,介电弹性薄膜的力学稳定是其作为驱动器的前提,除了力学的破坏、电击穿和力电失稳,屈曲/褶皱也是其稳定性研究的重要内容。本文基于超弹性本构和薄膜非线性大变形理论研究了介电弹性薄膜的屈曲失稳,获得了其屈曲条件和后屈曲行为特征,为该类材料在柔性驱动器中的应用提供了安全判据。另一方面,介电弹性薄膜的皱褶现象在显示功能部件、接触、润湿等领域有着潜在的应用,本文的研究为皱褶现象的充分利用提供了理论基础。

关键词：介电弹性体超弹性无基底薄膜褶皱

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In-situ observations on interphase boundary migration and grain growth during α/γ phase transformation in iron-4.2%Cr alloy

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材料与冶金学报 2005年第2期4卷 91-91页

作者：渡边忠雄 OBARA Kouichi TSUREKAWA Sadahiro 日本东北大学 Laboratory of Materials Design and Interface Engineering Department of Nanomechanics Graduate School of Engineering Tohoku University Sendai 980-8579 Japan Laboratory of Materials Design and Interface Engineering

In-situ observations on α/γ phase transformation were made to study the effects of grain boundary microstructures on the formation of a new phase and the migration of α/γ interphase boundary in an iron4. 2%Cr alloy. It was found that triple junctions with more random boundaries could be the primary nucleation sites for a new phase, while triple junctions with low angle or low ∑ coincidence boundaries did not play any role as preferential sites. The migration of α/γ interphase boundary during heating over the transformation temperature range showed the two stage behaviour characterized by a stage with a migration velocity of 0. 33-0. 75 mm/s and secondly by a stage with 3. 7-7. 6 mm/s. It was also found that abnormal grain growth and a high density of ∑3 coincidence boundaries could occur in a phase with bcc structure after cycling of α/γ phase transformation. A new mechanism of nucleation and growth of a new phase in α/γ phase transformation is proposed on the basis of roles of plane-matching interphase boundaries, as previously discussed on the origin of anisotropy of grain growth due to the migration of {110} plane-matching boundaries in Fe-3z%Si alloy. The most recent theoretical work on the distribution of plane-matching boundaries in solids with different crystal structures was found to be useful for the understanding of nucleation and growth during α/γ phase transformation.

关键词： In-situ phase velocity stage effects crystal with random origin the range after new was more play over high most for The to did bcc It be

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In Situ TEM Measurements of the Mechanical Properties and Behavior of WS_(2)Nanotubes

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Nano Research 2008年第1期1卷 22-31页

作者： Ming Sheng Wang Ifat Kaplan-Ashiri Xian Long Wei Rita Rosentsveig Hanoch Daniel Wagner Reshef Tenne Lian Mao Peng Key Laboratory on the Physics and Chemistry of Nanodevices and department of Electronics Peking UniversityBeijing 100871China department of Materials and Interfaces Weizmann Institute of ScienceRehovot 76100Israel

The mechanical properties of individual WS2 nanotubes were investigated and directly related to their atomic structure details by in situ transmission electron microscope measurements.A brittle mode deformation was observed in bending tests of short(ca.1μm in length)multilayer nanotubes.This mode can be related to the atomic structure of their shells.In addition,longer nanotubes(67μm in length)were deformed in situ scanning electron microscope,but no plastic deformation was detected.A“sword-in-sheath”fracture mechanism was revealed in tensile loading of a nanotube,and the sliding of inner shells inside the outermost shell was imaged“on-line”.Furthermore,bending modulus of 217 GPa was obtained from measurements of the electric-fi eld-induced resonance of these nanotubes.

关键词： Inorganic nanotubes nanomechanics TEM SEM

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An index for deformation controllability of small-volume materials

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Science China(Technological Sciences) 2014年第4期57卷 663-670页

作者： WANG ZhangJie SHAN ZhiWei LI Ju SUN Jun MA Evan Center for Advancing Materials Performance from the Nanoscale CAMP-Nano) & Hysitron Applied Research Center in China (HARCC) State Key Laboratory for Mechanical Behavior of Materials Xi'an Jiaotong University department of Nuclear Science and Engineering and department of Materials Science and Engineering Massachusetts Institute of Technology department of Materials Science and Engineering Johns Hopkins University

Mechanical tests on small-volume materials show that in addition to the usual attributes of strength and ductility,the controllability of deformation would be crucial for the purpose of precise plastic shaping.In our present work,a"mechanical controllability index"(MCI)has been proposed to assess the controllability of mechanical deformation quantitatively.The index allows quantitative evaluation of the relative fraction of the controllable plastic strain out of the total strain.MCI=0 means completely uncontrollable plastic deformation,MCI=∞means perfectly controllable plastic shaping.The application of the index is demonstrated here by comparing two example cases:0.273 to 0.429 for single crystal Al nanopillars that exhibit obvious strain bursts,versus 3.17 to 4.2 for polycrystalline Al nanopillars of similar size for which the stress-strain curve is smoother.

关键词：材料变形可控性小批量机械变形 MCI 力学测试塑料成形塑性应变

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