Beyond the Cutting-Edge: Highlights from Tribology Letter

Back by popular demand, the Beyond the Cutting-Edge plenary symposium presented by the editors of Tribology Letters highlights some of the best papers published in the peer-reviewed journal.

Wednesday, November 11, 2020

Sessions 6A 1:00 – 4:00 pm

1:00  - 1:30 pm 
3420392: Prediction of Nanoscale Friction for Two-Dimensional Materials Using a Machine Learning Approach 
Prathima Nalam, Behnoosh Sattari Baboukani, Kristofer Reyes, SUNY University at Buffalo, Buffalo, NY, Zhijiang Ye, Miami University, Oxford, OH 

Two-dimensional (2D) materials are emerging as alternatives for lubrication additives to control friction and wear in both dry and wet environments. Recent advances in data-driven and computational methods have enabled the discovery of more than 6000 3D materials with potential exfoliation properties, and hence the identification of 2D structures with optimum tribological properties necessities a machine learning approach. In this study, we employ Bayesian statistical analysis through the transfer learning approach to predict the maximum energy barrier (MEB) of the corrugated potential energy surface for a wide range of 2D materials. The MEB values predicted for 15 different 2D materials (across two families) while sliding similar layers of a 2D material against each other will enable the development of empirical relations among the descriptors (such as structure, thermal conductivity, etc.) associated with 2D materials and their intrinsic friction property. 

1:30 - 2 pm 
3429904: The Influence of Material and Electrical Current on the Formation of Premature Bearing Failures 

Benjamin Gould, Nick Demas, Rober Erck, Maria Cinta Lorenzo Martin, Aaron Greco, Argonne National Laboratory, Chicago, IL 

Premature fatigue failures associated with local regions of microstructural degradation (i.e. White Etching Cracks (WECs)) are the predominate mode of failure within wind turbine drivetrain bearings. Although WECs have been reported in the field for over a decade, the conditions leading to this failure, and the process by which this failure culminates, are both highly debated. Recently, it was documented levels of current up to 1A can be measured uptower in turbines. The presented work studies how this variable current effects component failure. The effect of lubricant formulation via variable base fluid and additive composition was also. Moreover, the effect of potential mitigation techniques such as the use of black oxide conversion layers, and other protective coatings will be presented. 

2:00 - 2:30 pm 
3435050: Walking Your Way to Thick Slippery Cartilage

David Burris, University of Delaware, Newark, DE 

The most basic questions about how cartilage and joint function remain unanswered despite nearly a century of research. For example, it is unclear if friction forces are attributable to classical adhesive interactions or fluid shear stresses, if rough interfaces are permeable or impermeable, or if the unusual roughness of cartilage has a purpose. In this talk, I will review our most interesting findings on the topic. I will start by demonstrating that the lubrication is simply proportional to near-surface hydration - as far as we can tell, high friction is impossible on hydrated cartilage surfaces and low friction is impossible on dehydrated surfaces. Next, I will discuss how cartilage maintains hydration and lubricity despite the leaky nature of the tissue. We show that walking reinflates cartilage and restores lubricity, thickness, and mechanical function. This surprising fact is a bit like driving a car to reinflate a leaky tire. Finally, we will discuss what our measurements suggest about the mechanics of this rehydration process and what it all implies for how we can mitigate our individual risk of cartilage dysfunction and disease. 

2:30 - 3 pm 
3436427: Graft Copolymers and Bottlebrushes at Surfaces for Tuning Physicochemical and Tribological Properties of Materials

Edmondo M. Benetti, ETH Zürich, Zürich, Switzerland 

The functionalization of inorganic and organic surfaces by highly branched, functional polymer adsorbates enables a fine tuning of the interfacial physicochemical properties and allows one to determine the interaction of the modified support with the surrounding environment. This is valid on metal oxide surfaces, where graft copolymers featuring different compositions and side chain topologies can assemble forming biopassive and lubricious interfaces. Alternatively, from similar inorganic substrates, bottlebrushes with controlled molar mass and side chain length can be grown exploiting controlled radical polymerization (CRP) methods, enabling a broad modulation of steric stabilization of the surface, and tuning its biopassivity and nanotribological properties. The design concepts and functionalization strategies applied for model inorganic materials can be additionally enlarged to complex tissue surfaces such as articular cartilage, where highly branched, biocompatible copolymers can replace structurally similar biomacromolecules responsible for protection and lubrication of the underlying tissue. In this contribution, the influence of polymer architecture and composition on the fabrication and properties of graft copolymer- and bottlebrush-based interfaces will be discussed, bringing the abovementioned cases as examples of highly-technologically-relevant applications.