Integration of contact size dependence and thermal activation in atomic friction

Zhang, Jiangnan; Lee, Jin Haeng; Lou, Jun; Gao, Yanfei

doi:10.1016/j.eml.2015.01.005

Cited by 2 publications

(4 citation statements)

References 20 publications

(27 reference statements)

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“…The transition between these two states experiences a saddle point configuration which has a higher energy than the stable solution, and the energy difference between the saddle point and stable configurations is the activation energy. Such a general view has be adopted for various types of dislocation models, including the Volterra dislocation analysis [91,[132][133][134], the Peierls dislocation model [135][136][137][138][139][140], or molecular dynamics [131,142]. The saddle point configuration can be guessed in simple cases, e.g., a circular dislocation loop in homogeneous dislocation nucleation, or a half loop from a crack tip or surface steps.…”

Section: Thermally Activated Dislocation Nucleation Processmentioning

confidence: 99%

Strength statistics of single crystals and metallic glasses under small stressed volumes

Gao¹,

Bei²

2016

Progress in Materials Science

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It has been well documented that plastic deformation of crystalline and amorphous metals/alloys shows a general trend of "smaller is stronger". The majority of the experimental and modeling studies along this line have been focused on finding and reasoning the scaling slope or exponent in the logarithmic plot of strength versus size. In contrast to this view, here we show that the universal picture should be the thermally activated nucleation mechanisms in small stressed volume, the stochastic behavior as to find the weakest links in intermediate sizes of the stressed volume, and the convolution of these two mechanisms with respect to variables such as indenter radius in nanoindentation pop-in, crystallographic orientation, pre-strain level, sample length as in uniaxial tests, and others. Experiments that cover the entire spectrum of length scales and a unified model that treats both thermal activation and spatial stochasticity have discovered new perspectives in understanding and correlating the strength statistics in a vast of observations in nanoindentation, micro-pillar compression, and fiber/whisker tension tests of single crystals and metallic glasses.

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Section: Thermally Activated Dislocation Nucleation Processmentioning

confidence: 99%

Strength statistics of single crystals and metallic glasses under small stressed volumes

Gao¹,

Bei²

2016

Progress in Materials Science

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“…For a Mode-II crack, the gradual increase of the relative shear displacement between surfaces S + and S − leads to the nucleation of an edge dislocation from the crack tip in figure 3(a). The total potential energy is written as [11,14,21]…”

Section: Problem Formulationmentioning

confidence: 99%

“…Much of the above complexities can be removed if a smooth single asperity can be examined at nanoscale. Along this line, frictional force microscopy tests have found the high friction stress (i.e., friction force divided by the contact area) that is a large fraction of the material shear modulus, the reduction of friction stress due to interface incommensurability, and the increase of the friction force with the increase of sliding velocity, among many others [2,[11][12][13][14]. The one-dimensional Tomlinson model, as commonly used in surface physics and tribology [1,2], assumes a point contact that is connected to the faraway loading apparatus by a compliant spring and traverses on a periodic potential that represents the atomic structure on the surface.…”

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Scale dependence of interface dislocation storage governing the frictional sliding of single asperities

Gao

Zhang

Gao

2016

Modelling Simul. Mater. Sci. Eng.

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Single-asperity friction tests have found a critical dependence of friction stress on the nanoscale contact size, as successfully explained by the nucleation of interface dislocations as opposed to concurrent sliding of all the interfacial atoms in contact. Modeling and simulation results, however, vary when the motion and interactions of multiple dislocations dominate at a larger scale regime. A Rice-Peierls framework is employed to investigate the multiplication and storage of interface dislocations, and the critical conditions for dislocation initiation and steadystate gliding are determined numerically. Our findings identify the key parameters that govern various friction mechanisms in the Hurtado-Kim and Deshpande-Needleman-van der Giessen models. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 Keywords IntroductionFriction is an inherently multiscale problem [1,2], because of the geometric irregularities (i.e., roughness, asperities) that prevail over multiple decades of length scales [3][4][5], the plastic responses that depend on intrinsic and extrinsic length scales such as geometrically necessary dislocations or material microstructures [6][7][8][9], and a variety of time-dependent processes that render peculiar rate-dependent, collective responses of multi-asperities at micro-and macroscales [10]. Much of the above complexities can be removed if a smooth single asperity can be examined at nanoscale. Along this line, frictional force microscopy tests have found the high friction stress (i.e., friction force divided by the contact area) that is a large fraction of the material shear modulus, the reduction of friction stress due to interface incommensurability, and the increase of the friction force with the increase of sliding velocity, among many others [2,[11][12][13][14]. The one-dimensional Tomlinson model, as commonly used in surface physics and tribology [1,2], assumes a point contact that is connected to the faraway loading apparatus by a compliant spring and traverses on a periodic potential that represents the atomic structure on the surface.Although the stick-slip behavior on the shear load-displacement curves can be successfully explained, it inexorably constrains all the atoms in contact moving concurrently. Although several dislocation-based models [11,[15][16][17] have emerged recently to resolve this limitation in the Tomlinson model, they appear to conflict each other in the underlying assumptions, as will be explained in Figs. 1 and 2. The present work aims to reconcile, and provide justifications for, the discrepancies in the Hurtado-Kim model [15,16] and the Deshpande-Needleman-van der Giessen model [17].In the Hurtado-Kim model in Fig. 1(a), the contacting bodies are equivalent to an external circular crack subjected to a tangential loading, thus leading to stress singularity at the contact edg...

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Integration of contact size dependence and thermal activation in atomic friction

Cited by 2 publications

References 20 publications

Strength statistics of single crystals and metallic glasses under small stressed volumes

Strength statistics of single crystals and metallic glasses under small stressed volumes

Scale dependence of interface dislocation storage governing the frictional sliding of single asperities

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