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Scale- and load-dependent friction in commensurate sphere-on-flat contacts

机译:相应的平面接触中与尺度和载荷有关的摩擦

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Contact of a spherical tip with a flat elastic substrate is simulated with a Green's-function method that includes atomic structure at the interface while capturing elastic deformation in a semi-infinite substrate. The tip and substrate have identical crystal structures with nearest-neighbor spacing d and are aligned in registry. Purely repulsive interactions between surface atoms lead to a local shear strength that is the local pressure times a constant local friction coefficient a. The total friction between tip and substrate is calculated as a function of contact radius a and sphere radius R, with a up to 10~3d and R up to 4 x 10~4d. Three regimes are identified depending on the ratio of a to the core width of edge dislocations in the center of the contact. This ratio is proportional to aa~2/Rd. In small contacts, all atoms move coherently and the total friction coefficient µ = a. When the contact radius exceeds the core width, a dislocation nucleates at the edge of the contact and rapidly advances to the center where it annihilates. The friction coefficient falls as µ ~ a(aa~2 / Rd)~(-2/3). An array of dislocations forms in very large contacts and the friction is determined by the Peierls stress for dislocation motion. The Peierls stress rises with pressure, and µ rises with increasing load.
机译:用格林函数方法模拟球形尖端与平坦的弹性基板的接触,该方法在界面处包含原子结构,同时捕获半无限基板中的弹性变形。尖端和基底具有相同的晶体结构,其最近邻间距为d,并且对准对齐。表面原子之间的纯排斥相互作用导致局部剪切强度,即局部压力乘以恒定的局部摩擦系数α。尖端与基材之间的总摩擦力是接触半径a和球体半径R的函数,最大可达10〜3d,R可达4 x 10〜4d。根据α与接触中心边缘位错核心宽度的比值,确定了三种状态。该比例与aa〜2 / Rd成正比。在小接触中,所有原子相干运动,总摩擦系数µ = a。当接触半径超过磁芯宽度时,位错在接触的边缘成核,并迅速前进到其消失的中心。摩擦系数为μ〜a(aa〜2 / Rd)〜(-2/3)。位错阵列在非常大的接触中形成,并且摩擦力由位错运动的Peierls应力确定。 Peierls应力随压力增加,而µ随着负荷增加而增加。

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  • 来源
    《Physical review. B, Condensed Matter And Materials Physics》 |2017年第15期|155436.1-155436.13|共13页
  • 作者单位

    Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA,Department of Physics, University of Pennsylvania, 209 South 33rd Street, Philadelphia, Pennsylvania 19104, USA;

    Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA,Department of Microsystems Engineering, University of Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany;

    Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA;

    Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA;

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