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Lithiation-enhanced charge transfer and sliding strength at the silicon-graphene interface:A first-principles study

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Acta Mechanica Solida Sinica 2017年第3期30卷 254-262页

作者： Cheng Chang Xiaoyan Li Zhiping Xu Huajian Gao Applied mechanics Laboratory Department of Engineering Mechanics Center for Nano and Micro MechanicsCenter for Advanced Mechanics and Materials Tsinghua University School of Engineering Brown University

The application of silicon as ultrahigh capacity electrodes in lithiumion batteries has been limited by a number of mechanical degradation mechanisms including fracture, delamination and plastic ratcheting, as a result of its large volumetric change during lithiation and delithiation. Graphene coating is one feasible technique to mitigate the mechanical degradation of Si anode and improve its conductivity. In this paper, first-principles calculations are performed to study the atomic structure, charge transfer and sliding strength of the interface between lithiated silicon and graphene. Our results show that Li atoms segre- gate at the （lithiated） Si-graphene interface preferentially, donating electrons to graphene and enhancing the interfacial sliding resistance. Moreover, the interfacial cohesion and sliding strength can be further enhanced by introducing single-vacancy defects into graphene. These findings provide insights that can guide the design of stable and efficient anodes of silicon/graphene hybrids for energy storage applications.

关键词： Lithium-ion batteries Silicon anode Graphene coating Interracial sliding strength First-principles calculations

Effects of static aeroelasticity on composite wing characteristics under different flight attitudes

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Journal of Central South University 2013年第2期20卷 312-317页

作者：霍世慧袁喆王富生岳珠峰 advanced materials Test center School of Mechanics and Civil Engineering & ArchitectureNorthwestern Polytechnical University

Composite wing static aeroelasticity was analyzed through a loosely coupled method and the effects on composite wing characteristics under different flight attitudes were presented. Structural analysis and aerodynamic analysis were carried out through finite element method (FEM) software NASTRAN and computational fluid dynamics (CFD) software FLUENT, respectively. Correlative data transfer and mesh regenerate procedure were applied to couple the results of computational structure dynamics (CSD) and CFD. After static aeroelasticity analysis under different flight attitudes, it can be seen that lift increases with the increase of flight speed and the incremental value enlarges gradually in both rigid and elastic wings. Lift presents a linear increment relationship with the increase of attack angle when the flight speed is 0.4Ma or 0.6Ma, but nonlinear increment in elastic wing when flight speed is 0.8Ma. On the effect of aeroelasticity, the maximum of deformation increases with the increase of flight speed and attack angle, and the incremental value decreases with the increase of flight speed while uniform with different attack angles. The results provide a reference for engineering applications.

关键词： static aeroelasticity elastic deformation aerodynamic characteristics structural characteristics flight attitudes

mechanics of flexible and stretchable piezoelectrics for energy harvesting

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Science China(Physics,mechanics & Astronomy) 2015年第9期58卷 39-51页

作者： CHEN Ying LU BingWei OU DaPeng FENG Xue Department of Engineering mechanics Tsinghua University center for mechanics and materials Tsinghua University

As rapid development in wearable/implantable electronic devices benefit human life in daily health monitoring and disease treatment medically, all kinds of flexible and/or stretchable electronic devices are booming, together with which is the demanding of energy supply with similar mechanical property. Due to its ability in converting mechanical energy lying in human body into electric energy, energy harvesters based on piezoelectric materials are promising for applications in wearable/implantable device's energy supply in a renewable, clean and life-long way. Here the mechanics of traditional piezoelectrics in energy harvesting is reviewed, including why piezoelectricity is the choice for minor energy harvesting to power the implantable/wearable electronics and how. Different kinds of up to date flexible piezoelectric devices for energy harvesting are introduced, such as nanogenerators based on Zn O and thin and conformal energy harvester based on PZT. A detailed theoretical model of the flexible thin film energy harvester based on PZT nanoribbons is summarized, together with the in vivo demonstration of energy harvesting by integrating it with swine heart. Then the initial researches on stretchable energy harvesters based on piezoelectric material in wavy or serpentine configuration are introduced as well.

关键词： piezoelectric effect energy harvesting flexible electronics stretchable electronics

Dynamic compressive behavior and constitutive relations of lanthanum metal

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Journal of Rare Earths 2012年第5期30卷 473-479页

作者：王焕然蔡灿元陈大年马东方邓高涛 mechanics and materials Science Research center Ningbo University

The dynamic compressive behavior and constitutive relations of Lanthanum（La） metal was determined by using the first compression in split Hopkinson pressure bar（SHPB） tests at different strain rates and *** constitutive relation of La metal determined in a certain range of strains was employed and adjusted in numerically simulating large deformations of La metal specimens generated by multi-compression in SHPB tests and recorded by a high-speed *** dynamic compressive behavior and constitutive relations of La metal under multiple SHPB tests loading was also *** results of scanning electron microscope（SEM） investigation of the recovered La metal specimens for typical tests showed that there was a variety of deformation microstructures depending on strain rate,temperature and stress state.

关键词： lanthanum metal dynamic compression constitutive relation multi-compression multiple impact SHPB rare earths

On the material constants measurement method of a fluid-saturated transversely isotropic poroelastic medium

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Science China(Physics,mechanics & Astronomy) 2019年第1期62卷 69-75页

作者： Yue Gao ZhanLi Liu Zhuo Zhuang Keh-Chih Hwang AML Department of Engineering Mechanics Tsinghua University center for mechanics and materials Tsinghua University

The fluid-saturated transversely isotropic poroelastic medium could be widely found in nature, e.g., the sedimentary rocks underground. To determine the eight independent material constants for the transversely isotropic poroelastic medium, a series of tests are discussed. Two undrained tests and one drained test are suggested as a set of tests of the least amount. For the verification purpose, two additional drained tests are also introduced as an option. The atmospheric dried test is discussed as a replacement of the traditional infiltrated drained test to save the time waiting for an equilibrium state. Some microscopic material constants, i.e.,the unjacketed bulk coefficients, the porosity, and the compressibility of porous fluid, are measurable but unnecessary to determine the independent material constants of a poroelastic medium.

关键词： poroelastic constitutive model material constants measurement transversely isotropic medium

Dynamic tensile characterization of pig skin

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Acta Mechanica Sinica 2014年第2期30卷 125-132页

作者： H.Khatam Q.Liu K.Ravi-Chandar center for mechanics of Solids Structures and MaterialsThe University of Texas at Austin

The strain-rate dependent response of porcine skin oriented in the fiber direction is explored under tensile loading. Quasi-static response was obtained at strain rates in the range of 10-3s-1to 25 s-1. Characterization of the response at even greater strain rates is accomplished by measuring the spatio-temporal evolution of the particle velocity and strain in a thin strip subjected to high speed impact loading that generates uniaxial stress conditions. These experiments indicate the formation of shock waves; the shock Hugoniot that relates particle velocity to the shock velocity and the dynamic stress to dynamic strain is obtained directly through experimental measurements, without any assumptions regarding the constitutive properties of the material.

关键词： Nonlinear waves Impact tests Digital image correlation Shocks Hugoniot

Improving the thermal shock resistance of ceramics by crack arrest blocks

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Science China(Technological Sciences) 2016年第6期59卷 913-919页

作者： WANG Yan Wei XIA Biao SU Hong Hong CHEN Hang FENG Xue Applied mechanics Laboratory Department of Engineering Mechanics Tsinghua University center for mechanics and materials Tsinghua University Department of Engineering mechanics Chongqing University

Ceramics used in the high temperature environment are inevitably subjected to sudden temperature change, which may lead to catastrophic thermal shock failure due to the intrinsic brittleness of ceramics. In this paper, an experimental platform is designed to realize the in-situ observation during the thermal shock experiments. Experimental results show that all the cracks initiate from one of the edge midpoints and propagate to another one for square specimens. Such experimental observation is consistent with the maximum tensile stress zone with the maximum temperature gradient given by the finite element method(FEM). The different crack modes resulting from different heating rates after thermal shock experiments are observed and analyzed. Comparison between different clamping methods is conducted to study the effects of boundary conditions on the thermal shock experiments. Furthermore, in order to improve the thermal shock performance of alumina ceramics, crack arrest blocks are added near the edge midpoint. The thickness, shape and arrangement of the blocks are systematically investigated to understand the mechanism of improvement of thermal shock resistance.

关键词： thermal shock ultra-high temperature ceramics crack arrest blocks in-situ dynamic observation

Analyses of mechanically-assembled 3D spiral mesostructures with applications as tunable inductors

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Science China(Technological Sciences) 2019年第2期62卷 243-251页

作者： ZHANG Fan LIU Fei ZHANG YiHui Key Laboratory of Applied mechanics of Ministry of Education Department of Engineering Mechanics Tsinghua University center for Flexible Electronics Technology and center for mechanics and materials Tsinghua University

Mechanically-guided assembly allows the formation of 3D spiral-shaped inductors through controlled buckling, which could provide an increased quality(Q) factor and broadened working angle in near field communication, as compared to the planar design. An understanding of the microstructure-property relationship is essential in the design optimization of the assembly process. This work presents a theoretical model to analyze the deformations during the assembly of the 3D spiral-shaped mesostructure from a bilayer precursor that consists of a supporting ribbon and a 2D coil on its top. As validated by both the experiments and finite element analyses(FEA), this mechanics model allows accurate predictions of the assembled 3D configurations. In combination of electromagnetic simulations, we investigated the effects of various key design parameters on the final 3D configuration and the Q factor when operated as an inductor. The results suggest a significant role of the gravity effect on the assembled spiral configuration, especially for flexible coil designs with relative small cross-sectional areas or long *** study can serve as a reference for the design of spiral-shaped 3D inductors in different device applications.

关键词： 3D assembly modeling buckling multilayer tunable inductor

Dendritic and spherical crystal reinforced metallic glass matrix composites

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International Journal of Minerals,Metallurgy and materials 2013年第4期20卷 386-392页

作者： Jun-wei Qiao Yong Zhang Hui-jun Yang Sheng-bo Sang Laboratory of Applied Physics and mechanics of advanced materials College of Materials Science and Engineering Taiyuan University of Technology Key Laboratory of Interface Science and Engineering in advanced materials (Ministry of Education) Taiyuan University of Technology State Key Laboratory for advanced Metals and materials University of Science and Technology Beijing MicroNano System Research center Taiyuan University of Technology

Zr-based bulk metallic glass matrix composites （BMGMCs） with a composition of Zr60.0Ti14.7Nb5.3Cu5.6Ni4.4- Be10.0 （at%） were fabricated by an innovative process, i.e., semisolid processing plus Bridgman solidification. Different morphologies, distributions, and volume fractions of the crystalline phases can be achieved by tailoring the withdrawal velocity. The largest fi-acture strain of Zr60.0Ti14.7Nb5.3Cu5.6Ni4.4Be10.0 （at%） composites with the withdrawal velocity of 1.0 mm/s was found to be 16.7%. The mechanism of plasticity improvement is mainly attributed to the interpenetrated structure of the crystalline phase, which greatly confines the rapid propagation of shear bands.

关键词： metallic glass composite materials mechanical properties plastic deformation