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Snapping instability in prismatic tensegrities under torsion

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Applied Mathematics and Mechanics(English Edition) 2016年第3期37卷 275-288页

作者： Liyuan ZHANG Cheng ZHANG Xiqiao FENG Hua jian GAO School of Mechanical Engineering University of Science and Technology Beijing aml & cnmm Department of Engineering Mechanics Tsinghua University School of Engineering Brown University

Tensegrities are a class of lightweight and reticulated structures consisting of stressed strings and bars. It is shown that each prismatic tensegrity can have two self-equilibrated and stable states, leading to a snapping instability behavior under an applied torque. The predicted mechanism is experimentally validated, and can be used in areas such as advanced sensors and actuators, energy storage /alsorption equipments, and folding/unfolding devices.

关键词： tensegrity snapping instability mechanical response structure mechanics

Energy corrugation in atomic-scale friction on graphite revisited by molecular dynamics simulations

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Acta Mechanica Sinica 2016年第4期32卷 604-610页

作者： Xiao-Yu Sun Yi-Zhou Qi Wengen Ouyang Xi-Qiao Feng Qunyang Li aml and cnmm Department of Engineering MechanicsTsinghua University Department of Engineering Mechanics School of Civil Engineering Wuhan University State Key Laboratory of Tribology Tsinghua University

Although atomic stick–slip friction has been extensively studied since its first demonstration on graphite,the physical understanding of this dissipation-dominated phenomenon is still very limited. In this work, we perform molecular dynamics（MD） simulations to study the frictional behavior of a diamond tip sliding over a graphite surface. In contrast to the common wisdom, our MD results suggest that the energy barrier associated lateral sliding（known as energy corrugation） comes not only from interaction between the tip and the top layer of graphite but also from interactions among the deformed atomic layers of graphite. Due to the competition of these two subentries, friction on graphite can be tuned by controlling the relative adhesion of different *** relatively low tip-graphite adhesion, friction behaves normally and increases with increasing normal load. However,for relatively high tip-graphite adhesion, friction increases unusually with decreasing normal load leading to an effectively negative coefficient of friction, which is consistent with the recent experimental observations on chemically modified graphite. Our results provide a new insight into the physical origins of energy corrugation in atomic scale friction.

关键词： graphite friction diamond sliding tuned stick dissipation decreasing chemically oscillatory

HEAT FLOW CONTROL BY TRANSFORMATION METHOD WITH GRID GENERATION METHOD

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Acta Mechanica Solida Sinica 2014年第5期27卷 454-460页

作者： Zheng Chang Xiaoning Liu Gengkai Hu Key Laboratory of Dynamics and Control of Flight Vehicle Ministry of Education School of Aerospace Engineering Beijing Institute of Technology cnmm & aml Department of Engineering Mechanics Tsinghua University

In the context of the transformation method, we propose a general approach to construct numerically the mapping generated by imposing specific boundary conditions with a targeted function, and the necessary material and heat source spatial distributions are then derived with the help of transformation method. The construction of mapping by grid generation method through solving partial differential equations circumvents the limitation of device geometry, which paves the way for designing more complex heat flow control devices. Two numerical examples are also given to show how to design material properties and heat source in order to control temperature patterns.

关键词： heat conduction inverse problem transformation method grid generation

Quantitative law of diffusion induced fracture

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Acta Mechanica Sinica 2016年第4期32卷 611-632页

作者： H.-J.Lei H.-L.Wang B.Liu C.-A.Wang aml CNMMDepartment of Engineering MechanicsTsinghua UniversityBeijing 100084China State Key Lab of New Ceramics and Fine Processing Department of Materials Science and EngineeringTsinghua UniversityBeijing 100084China

Through dimension analysis, an almost analytical model for the maximum diffusion induced stress（DIS）and critical temperature（or concentration） difference at which cracks begin to initiate in the diffusion process is developed. It interestingly predicts that the spacing of diffusioninduced cracks is constant, independent of the thickness of specimen and the temperature difference. These conclusions are validated by our thermal shock experiments on alumina plates. Furthermore, the proposed model can interpret observed hierarchical crack patterns for high temperature jump cases, and a three-stage relation between the residual strength and the temperature difference. The prediction for crack spacing can guide the biomimetic thermal-shockfailure proof design, in which the hard platelets smaller than the predicted diffusion induced by constant crack-spacing are embedded in a soft matrix, and, therefore, no fracture will happen. This may guide the design of the thermal protection system and the lithium ion battery. Finally we present the maximum normalized DISes for various geometry and boundary conditions by single-variable curves for the stressindependent diffusion process and two-variable contour plots for the stress-dependent diffusion process, which can provideengineers and materialists a simple and easy way to quickly evaluate the reliability of related materials and devices.

关键词： normalized hierarchical contour spacing quickly lithium validated battery constraint coordinate

The Existence of Simultaneous Bragg and Locally Resonant Band Gaps in Composite Phononic Crystal

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Chinese Physics Letters 2013年第4期30卷 110-114页

作者： XU Yan-Long CHEN Chang-Qing TIAN Xiao-Geng State Key Laboratory for Mechanical Structure Strength and Vibration Xi'an Jiaotong UniversityXi'an 710049 Department of Engineering Mechanics AML&CNMMTsinghua UniversityBeijing 100084

The band structure and transmission coefficient of the two-dimensional ternary locally resonant phononic crystal are computed by the finite element method with the calculated frequency up to 120 *** band gap in the high frequency range is found and considered as the Bragg band gap in the locally resonant phononic crystal which has the locally resonant band gap in the low frequency range ***,a composite phononic crystal by hybridizing the Bragg scattering phononic crystal and the locally resonant phononic crystal is *** Bragg and locally resonant band gaps are displayed and discussed for the composite phononic *** results show that the simultaneous Bragg band gap and locally resonant band gap can be tuned.

关键词： resonant locally crystal

Mechanical Analysis and Strength Checking of Current Collector Failure in the Winding Process of Lithium-Ion Batteries

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Acta Mechanica Solida Sinica 2021年第3期34卷 297-306页

作者： Ran Tao Zhibo Liang Shengxin Zhu Le Yang Lianhua Ma Wei-li Song Haosen Chen aml CNMMDepartment of Engineering MechanicsTsinghua UniversityBeijing 100084China Institute of Advanced Structure Technology Beijing Institute of TechnologyBeijing 100081China College of Civil Engineering and Architecture Hebei UniversityBaoding 071002China

The current collector fracture failure of lithium-ion batteries(LIBs)occurs during its winding production process frequently,and the consequent damages are usually large,but little research has been conducted on this *** work stems from the difficulty and obstacles in the winding process of actual production of *** fracture failure of the current collectors is easily caused by the evolution and mutation of the mechanical behavior during the winding process,resulting in safety hazards and poor *** purpose of this work is to reveal the evolution and distribution mechanism of circumferential strain of the current collectors on the fracture failure under the constraint of winding *** tests,finite element calculations and theoretical model are used to study the evolution and distribution of circumferential *** dynamic evolution process of circumferential strain is tested accurately,and the mechanism of fracture failure of current collectors is *** criterion for current collector strength is proposed based on the results of strain analysis and SEM observation.

关键词： Lithium-ion batteries Circumferential strain Mechanical properties Surface damage Strength checking

Three dimensional phase field study on the thickness effect of ferroelectric polymer thin film

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Theoretical & Applied Mechanics Letters 2011年第1期1卷 34-37页

作者： Tao Li,~(1,a))Changqing Chen,~(2,b)) and Jinxiong Zhou~1 1)School of Aerospace,Xi’an Jiaotong University,Xi’an 710049,China 2)Department of Engineering Mechanics,aml & cnmm,Tsinghua University,Beijing 100084,China Department of Engineering Mechanics AML & CNMM Tsinghua University Beijing 100084 China

The electromechanical behavior of poly(vinylidene fluoride-trifluoroethylene)[P(VDF -TrFE)]ferroelectric thin film was investigated using the three dimensional(3D) phase-field method. Various energetic contributions,including elastic,electrostatic,and domain wall energy were taken into account in the variational functional of the phase field *** of the microscopic domain structures of P(VDF-TrFE) polymer film was *** of the in-plane residual stress,the film thickness and externally applied electric bias field on the electromechanical properties of the film were *** obtained numerical results showed that the macroscopic responses of the electric hysteresis loops are sensitive to the residual stress and electric bias *** was also found that thickness has a great effect on the electric hysteresis loops and remanent polarization.

关键词： phase field ferroelectric polymer thin film domain structure residual stress polarization

Surface effects on the persistence length of nanowires and nanotubes

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Theoretical & Applied Mechanics Letters 2014年第5期4卷 54-59页

作者： Hua Liu Hualong Song Xiqiao Feng Jialing Yang Institute of Solid Mechanics Beihang University aml and cnmm Department of Engineering MechanicsTsinghua University

Surface effects on the persistence length of quasi-one-dimensional nanomaterials are investigated by using the theory of surface elasticity and the core-shell model of nanobeams. A simple and unified expression is provided to determine the persistence length of nanowires and nanotubes with any regular polygonal cross-sections. It is demonstrated that surface effects have a distinct in- fluence on the persistence length when the characteristic sizes of materials shrink to nanometers. This work is helpful not only for understanding the size-dependent behavior of nanomaterials but also for the design of devices based on nanotubes or nanowires.

关键词： surface effect persistence length nanotube nanowire

Two-dimensional modeling of the self-limiting oxidation in silicon and tungsten nanowires

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Theoretical & Applied Mechanics Letters 2016年第5期6卷 195-199页

作者： Mingchao Liu Peng Jin Zhiping Xu Dorian A.H.Hanaor Yixiang Gan Changqing Chen Department of Engineering Mechanics CNMM & AMLTsinghua University School of Civil Engineering The University of Sydney

Self-limiting oxidation of nanowires has been previously described as a reaction- or diffusion-controlled process. In this letter, the concept of finite reactive region is introduced into a diffusion-controlled model, based upon which a two-dimensional cylindrical kinetics model is developed for the oxidation of silicon nanowires and is extended for tungsten. In the model, diffusivity is affected by the expansive oxidation reaction induced stress. The dependency of the oxidation upon curvature and temperature is modeled. Good agreement between the model predictions and available experimental data is obtained. The de- veloped model serves to quantify the oxidation in two-dimensional nanostructures and is expected to facilitate their fabrication via thermal oxidation techniques.

关键词： Self-limiting oxidation Finite reactive region Kinetics model Nanowires