Abstract
In this study, a novel apparatus was designed and constructed to perform micro-sliding friction experiments while simultaneously observing the motion of micro-sized spheres using a visual inspection technique. The apparatus comprises a precision elevation stage that is used to elevate a flat mica disk, with the microspheres on top of it, to bring it into contact with a stationary surface and apply low loads on the contact. During micro-sliding experiments, it was found that the velocity of the center of the microsphere was half the velocity of the mica disk; in addition, friction force measurements revealed a very low coefficient of friction (about 0.03), indicating the rolling motion of the microspheres. The main outcome of our study was the verification of the hypothesis that spherical particles can be used to avoid direct contact among flat surfaces and can also introduce rolling motion within the system. The pure rolling motion of the microspheres sandwiched between a stationary and a moving flat surface supports the idea of adding rigid spherical particles to oil lubricants to further reduce friction and wear in the system by performing as micro and nanoscale ball bearings.
Highlights
Most mechanical systems involve energy losses due to the presence of friction and wear between moving surfaces
High frictional force and wear loss arises in boundary and mixed lubrication regions since fluid lubricant film thickness is less than 1 μm [1]
It has been shown that the combination of metal nanoparticles with two-dimensional nanosheets is an efficient method to improve the tribological properties of polymers [4]
Summary
Most mechanical systems involve energy losses due to the presence of friction and wear between moving surfaces. Liquid lubricants are used to lower wear and frictional losses by minimizing direct surface contact. High frictional force and wear loss arises in boundary and mixed lubrication regions since fluid lubricant film thickness is less than 1 μm [1]. In boundary and mixed lubrication regions, asperities interaction happens even with the existence of a liquid lubricant and, as a result, high wear and friction occur. Numerous research studies have been dedicated to advance the tribological properties of existing liquid lubricants. Recent research reports have pointed to the promising tribological results of nanoparticles when combined with 2D materials such as graphene. It has been shown that metal nanoparticle/graphene nanocomposites can be utilized as superior lubricant additive materials as well as solid lubricants or as film lubrication because of their exceptional self-lubricating properties [2]. It has been shown that the combination of metal nanoparticles with two-dimensional nanosheets is an efficient method to improve the tribological properties of polymers [4]
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