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Size and strain rate effects in tensile strength of penta-twinned Ag nanowires

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Acta Mechanica Sinica 2017年第4期33卷 792-800页

作者： Xuan Zhang Xiaoyan Li huajian gao Centre of Advanced Mechanics and Materials Department of Engineering Mechanics Tsinghua University School of Engineering Brown University

Penta-twinned Ag nanowires（pt-AgNWs） have recently attracted much attention due to their interesting mechanical and physical properties. Here we perform largescale atomistic simulations to investigate the influence of sample size and strain rate on the tensile strength of pt-AgNWs. The simulation results show an apparent size effect in that the nanowire strength（defined as the critical stress for dislocation nucleation） increases with decreasing wire diameter. To account for such size effect, a theoretical model involving the interaction between an emerging dislocation and the twin boundary has been developed for the surface nucleation of dislocations. It is shown that the model predictions are in quantitative agreement with the results from atomistic simulations and previous experimental studies in the literatures. The simulations also reveal that nanowire strength is strain-rate dependent, which predicts an activation volume for dislocation nucleation in the range of 1–10b^3,where b is the magnitude of the Burgers vector for a full dislocation.

关键词： nucleation tensile dislocation modulus apparent diameters decreasing magnitude crystalline penta

Atomistic modelling of deformation and failure mechanisms in nanostructured materials

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National Science Review 2015年第2期2卷 133-135页

作者： Xiaoyan Li huajian gao Department of Engineering Mechanics Tsinghua University School of Engineering Brown University

Over the past two decades,there has been a whirlwind of worldwide research activities on nanostructured materials,with the long-term promise to tailor-design material properties from the nanoscale and *** this grand e... 详细信息

关键词： MD Atomistic modelling of deformation and failure mechanisms in nanostructured materials

Two-dimensional model of vesicle adhesion on curved substrates

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Acta Mechanica Sinica 2006年第6期22卷 529-535页

作者： Wendong Shi Xi Qiao Feng huajian gao Department of Engineering Mechanics Tsinghua University Beijing 100084 China Division of Engineering Brown University 182 Hope Street Providence RI 02912 USA

We develop a two dimensional model of a vesicle adhered on a curved substrate via long-range molecular interactions while subjected to a detachment force. The relationship between the force and displacement of the vesicle is investigated as a function of the substrate shape. It is shown that both the force- displacement relationship and the maximum force at pull-off are significantly dependent on the substrate shape. The results suggest that probes with different tip shapes may be designed for cell manipulation. For example, we demonstrate that a vesicle can be pulled off a fiat surface using a probe with a curved tip.

关键词： Biomechanics Cell adhesion-Vesicle Adhesive contact Cell manipulation

Modeling Frequency- and Temperature-Invariant Dissipative Behaviors of Randomly Entangled Carbon Nanotube Networks under Cyclic Loading

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Nano Research 2011年第12期4卷 1191-1198页

作者： Xiaodong Yang Pengfei He huajian gao School of Aerospace Engineering and Applied Mechanics Tongji University Shanghai 200092 China School of Engineering Brown University Providence RI 02912 USA

Recent experiments have shown that entangled networks of carbon nanotubes exhibit temperature- and frequency-invariant dissipative behaviors under cyclic loading. We have performed coarse-grained molecular dynamics simulations which show that these intriguing phenomena can be attributed to the unstable attachments/detachments between individual carbon nanotubes induced by van der Waals interactions. We show that this behavior can be described by a triboelastic constitutive model. This study highlights the promise of carbon nanomaterials for energy absorption and dissipation under extreme conditions.

关键词： Carbon nanotubes unstable detachments and attachments van der Waals interactions triboelastic

Molecular dynamics simulation of peeling a DNA molecule on substrate

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Acta Mechanica Sinica 2005年第3期21卷 249-256页

作者： Xinghua Shi Yong Kong Yapu Zhao huajian gao Max-Planck Institut für Metallforschung Heisenbergstr. 3 D-70569 Stuttgart Germany State Key Laboratory of Nonlinear Mechanics (LNM) Institute of Mechanics Chinese Academy of Sciences. Beijing 100080 China

Molecular dynamics （MD） simulations are performed to study adhesion and peeling of a short fragment of single strand DNA （ssDNA） molecule from a graphite surface. The critical peel-off force is found to depend on both the peeling angle and the elasticity of ssDNA. For the short ssDNA strand under investigation, we show that the simulation results can be explained by a continuum model of an adhesive elastic band on substrate. The analysis suggests that it is often the peak value, rather than the mean value, of adhesion energy which determines the peeling of a nanoscale material.

关键词： Molecular dynamics simulation DNA Adhesion Peeling

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

Anomalous strain effect on the thermal conductivity of low-buckled two-dimensional silicene

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National Science Review 2021年第9期8卷 23-31页

作者： Bin Ding Xiaoyan Li Wuxing Zhou Gang Zhang huajian gao Institute of High Performance Computing A*STAR Centre for Advanced Mechanics and Materials Applied Mechanics Laboratory Department of Engineering Mechanics Tsinghua University School of Materials Science and Engineering & Hunan Provincial Key Laboratory of Advanced Materials for New Energy Storage and Conversion Hunan University of Science and Technology School of Mechanical and Aerospace Engineering College of Engineering Nanyang Technological University

The thermal conductivity of two-dimensional materials, such as graphene, typically decreases when tensile strain is applied, which softens their phonon modes. Here, we report an anomalous strain effect on the thermal conductivity of monolayer silicene, a representative low-buckled two-dimensional (LB-2D)material. Reax FF-based molecular dynamics simulations are performed to show that biaxially stretched monolayer silicene exhibits a remarkable increase in thermal conductivity, by as much as 10 times the freestanding value, with increasing applied strain in the range of [0, 0.1], which is attributed to increased contributions from long-wavelength phonons. A further increase in strain in the range of [0.11, 0.18] results in a plateau of the thermal conductivity in an oscillatory manner, governed by a unique dynamic bonding behavior under extreme loading. This anomalous effect reveals new physical insights into the thermal properties of LB-2D materials and may provide some guidelines for designing heat management and energy conversion devices based on such materials.

关键词： low-buckled two-dimensional materials strain effect thermal conductivity bonding dynamics

Remarkable enhancement in failure stress and strain of penta-graphene via chemical functionalization

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Nano Research 2017年第11期10卷 3865-3874页

作者： Yingyan Zhang Qingxiang Pei Zhendong Sha Yongwei Zhang huajian gao School of Computing Engineering and Mathematics Western Sydney University Penrith NSW2751 Australia Institute of High Performance Computing A＊STAR Singapore 138632 Singapore International Center for Applied Mechanics State Key Laboratory for Strength and Vibration of Mechanical Structures Xi'an Jiaotong University Xi'an 710049 China School of Engineering Brown University Providence Rhode Island 02912 USA

Penta-graphene （PG）,a newly proposed two-dimensional material composed entirely of carbon pentagons,is believed to possess much lower failure stress and strain than those of *** open question is whether and how these properties can be *** using molecular dynamics simulations,we examine the deformation and failure processes of PG functionalized with different functional *** reveal that complete chemical functionalization leads to remarkable increases in the failure stress and strain of PG by up to 86.6% and 82.4%,*** underlying reason for this enhancement is that the buckled pentagonal rings in pristine and partially functionalized PGs can easily transform into planar polygon rings under stretching;in contrast,complete functionalization of PG strongly stabilizes its structure and prevents such transformation,thereby significantly increasing the failure stress and *** findings suggest a possible route to enhance the mechanical properties of PG for potential applications in nanocomposites and nanodevices.

关键词： penta-graphene mechanical properties chemical functionalization molecular dynamics

MECHANICS OF CARBON NANOSCROLLS: A REVIEW

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Acta Mechanica Solida Sinica 2010年第6期23卷 484-497页

作者： Xinghua Shi Nicola M. Pugno huajian gao School of Engineering Brown University 610 Barus & Holley 182 Hope Street Providence RI 02912 USA Laboratory of Bio-inspired Nanomechanics 'Giuseppe Maria Pugno ' Department of Structural Engineering Politecnico di Torino Corso Duca degli Abruzzi 24 10129 Torino Italy

Carbon nanoscrolls （CNSs） belong to the same class of carbon-based nanomaterials as carbon nanotubes but are much less studied in spite of their great potential for applications in nanotechnology and bioengineering. Fundamental description, understanding and regulation of such materials will ultimately lead to a new generation of integrated systems that utilize their unique properties. In this review, we describe some of the recent advances in theoretical investi- gation on structural and dynamical behavior of CNS, as well as relevant simulation techniques. Theoretically it has been found that a stable equilibrium core size of CNS can be uniquely determined or tuned from the basal graphene length, the interlayer spacing, the interaction energy between layers of CNS and the bending stiffness of graphene. Perturbations of the surface energy, which can be controlled by an electric field, will cause a CNS to undergo breathing oscillatory motion as well as translational rolling motion on a substrate. The tunable core size of CNS also enables it to serve potentially as transmembrane water channels in biological systems.

关键词： Graphene