basic processes (e.g., phonon generation and electron–hole pair creation); thus, determining energy dissipation mechanisms offers the potential to control friction in new ways. [ 3–5 ] Theoretically, when an object is moving along an insulator surface, kinetic energy is dissipated solely through phonon emission (i.e., lattice vibration of the substrate). However, if the substrate is conductive,...

We study the dependence of friction on surface roughness, sliding velocity, and temperature. Expanding on the classic treatment of Greenwood and Williamson, we show that the fractal nature of a surface has little influence on the real area of contact and the static friction coefficient. A simple scaling argument shows that the static friction exhibits a weak anomaly mu ~ A(0)(-chi/4), where A0 ...

Typical holding force of piezo motors is defined by friction force, required to make motor move. However, increase of friction force is not inconsequent for motor performances in terms of speed, max motion force and lifetime (tribology). In this paper, a new motor, offering high resolution positioning and holding position when unpowered, is presented. Based on a Stepping Piezo Actuator [1] at i...

We measure the quasistatic friction force acting on intruders moving downwards into a granular medium. By utilizing different intruder geometries, we demonstrate that the force acts locally normal to the intruder surface. By altering the hydrostatic loading of grain contacts by a sub-fluidizing airflow through the bed, we demonstrate that the relevant frictional contacts are loaded by gravity r...

To study how macroscopic friction phenomena originate from microscopic junction laws, we introduce a general statistical framework describing the collective behavior of a large number of individual microjunctions forming a macroscopic frictional interface. Each microjunction can switch in time between two states: a pinned state characterized by a displacement-dependent force and a slipping stat...

Using molecular-beam-epitaxy-grown InAs and InSb on InP~001! surfaces, we show that the friction-force microscope is sensitive to monolayer coverage. Those surfaces are characterized by three-dimensional islands separated by flat regions. For a constant load, the frictional forces measured on the InAs island and on the substrate are the same. This is due to the formation of a two-dimensional we...

We present a comprehensive nanoscale tribological characterization of single-layer graphene grown by chemical vapor deposition (CVD) and transferred onto silicon oxide (SiO2) substrates. Specifically, the nanotribological properties of graphene samples are studied via atomic force microscopy (AFM) under ambient conditions using calibrated probes, by measuring the evolution of friction force wit...

When pulling a particle in a driven granular fluid with constant force Fex, the probe particle approaches a steady-state average velocity v. This velocity and the corresponding friction coefficient of the probe ζ=Fex/v are obtained within a schematic model of mode-coupling theory and compared to results from event-driven simulations. For small and moderate drag forces, the model describes the s...

For the successful development and application of lubricants, a full understanding of their complex nanoscale behavior under a wide range of external conditions is required, but this is difficult to obtain experimentally. Nonequilibrium molecular dynamics (NEMD) simulations can be used to yield unique insights into the atomic-scale structure and friction of lubricants and additives; however, th...

metal forming processes, compared with machining ones, reduce production steps and increasemanufacturing speed in addition to saving raw material. in this paper, forming process of column ofa steering mechanism is investigated by finite element analyses and experimental tests; andoptimum die design parameters are found. forming process parameters including die opening angle,bearing length, clea...