Scaling Effects on Materials Tribology: From Macro to Micro Scale

Abstract

The tribological study of materials inherently involves the interaction of surface asperities at the micro to nanoscopic length scales. This is the case for large scale engineering applications with sliding contacts, where the real area of contact is made up of small contacting asperities that make up only a fraction of the apparent area of contact. This is why researchers have sought to create idealized experiments of single asperity contacts in the field of nanotribology. At the same time, small scale engineering structures known as micro- and nano-electromechanical systems (MEMS and NEMS) have been developed, where the apparent area of contact approaches the length scale of the asperities, meaning the real area of contact for these devices may be only a few asperities. This is essentially the field of microtribology, where the contact size and/or forces involved have pushed the nature of the interaction between two surfaces towards the regime where the scale of the interaction approaches that of the natural length scale of the features on the surface. This paper provides a review of microtribology with the purpose to understand how tribological processes are different at the smaller length scales compared to macrotribology. Studies of the interfacial phenomena at the macroscopic length scales (e.g., using in situ tribometry) will be discussed and correlated with new findings and methodologies at the micro-length scale.

The Fundamental Regularities of the Evolution of Elastic Vortices Generated in the Surface Layers of Solids under Tangential Contact Loading

“…This provides the formation of "high-energy" elastic vortices with high shear stresses in the central region. In real contact pairs, the asperity sizes and the squares of the local contact spots of asperities are typically distributed over several orders of scales [3,5,6,45]. The asperities of the smallest spatial scales can lose the contact and start to slip already at the initial phase of the surface tangential displacement.…”

Practice of Simulation and Life Cycle Assessment in Tribology—A Review

“…Pin on disk (POD) and ball on disk (BOD) configurations are the two most widely used tribological test configuration that are reported in the literature and contact size between surfaces are in the range 50 to 800 µm in the macro-scale and between 0.06 and 6 µm in micro-scale [127]. As a rule of thumb, the contact area between tribo-contacts at the micro-scale tribology is about five orders of magnitude lower compared to the macro-scale tribology [127]. This affects the friction forces and surface tension in addition to the influence of contact shape and surface roughness.…”

“…In that respect, multi-scale modeling techniques that involve machine learning and deep learning are foreseen to play an important role [94,118,135]. Figure 10 represents the general overview of different length-scale investigation as reported in Reference [127]. materials at atomic scale, such as using the average distance, potential energy, or the distance-based limits for the structure of the materials [132].…”

“…Figure 10 represents the general overview of different length-scale investigation as reported in Reference [127]. [127]. This figure is taken from Reference [127] with permission from the publisher.…”

“…However, using a computational technique such as FEM or MD provides more information about initial surface conditions and atomic Figure 10. Different length scale (i.e., macro, micro, and nano) investigations used in tribology [127]. This figure is taken from Reference [127] with permission from the publisher.…”