Spotlight Presentations

Spotlight presentations are a special category of talks being presented during the Tribology Frontiers Virtual Conference featuring comprehensive longer (40-minute) presentations that have been chosen by the Tribology Frontiers Conference Planning Committee, with notable principal investigators (PIs) and researchers showcasing their most compelling tribology research to a broader audience.

All TFC spotlight presentations will be recorded and archived on-demand after the event ends for your convenience. Speakers/presenters will be asked to join the online chat discussions for each session and answer questions posted.

Monday, November 9

Session 2A - Energy, Environment & Manufacturing II

2:00 - 2:40 pm
3439417: Study of Vibration Wear in Plug-In Hybrid Vehicle Engine
Weizi Li, Shell (Shanghai) Technology Limited., Shanghai, China, Yunfei Wang, Qinhao Fan, Zhi Wang, Tsinghua University, Beijing, China, Taylor Robert, Shell Global Solutions UK, London, United Kingdom 

At times plug-in hybrid vehicle (PHEV) is powered only by electricity, hence engine does not operate and is not lubricated well, subsequently is under severer stress of vibration on road. Thus, this study initiated by Shell and Tsinghua University is aimed to identify possible lubrication challenge in such case. As first step, vibration data acquisition from a PHEV is done through dynamometer and real driving, amplitude and frequency characteristics of engine vibration are analyzed. Next, in order to simulate extreme conditions in pure electricity mode, the PHEV engine is installed on a specifically designed rig to produce accelerated aging resulting from vibration. Lastly, engine is teared down for measurement and rating. The test results suggest fretting wear can be intensified in PHEV as we find corrosion-like wear pattern on the journal bearing close to fly wheel and scratches which indicated abrasive wear on con-rod bearings.

Tuesday November 10

Session 3B - Surface & Interfaces III

2:00 - 2:40 pm
3439430: Chemical and Physical Origins of Friction on Two-Dimensionally Flat Surface with Atomic Steps

Seong Kim, Pennsylvania State University, State College, PA 

When two solid surfaces are in contact and shear each other, there is always a friction. Depending on the materials involved and the chemistry of surrounding environments, friction coefficient can be even larger than 1 or as small as <0.01. What governs such a large variance in friction coefficient? To better understand the origins of friction, we studied friction on a chemically and topographically well-defined interface—a graphite step edge—using atomic force microscopy and molecular dynamics simulations. We identified the separate contributions of physical and chemical processes to friction and showed that friction coefficient can be separated into two terms corresponding to these effects. We also found that the friction force measured with an AFM tip moving across an atomic step edge does not positively correlate with the adhesion force measured with the same tip at the same step edge. The findings provide deeper insights into the chemical and topographic origins of friction.

Session 3C - Lubricants I

10:00 - 10:40 am
3435312: Mechanochemistry at Diamond-Rock Interfaces
Jagjeevan Bhamra, James Ewen, Daniele Dini, Imperial College London, London, United Kingdom, Marc Bird, John Bomidi, Baker Hughes, Houston, TX 

The interactions between polycrystalline diamond compact (PDC) drill bits and rock-surfaces is not fully understood. We perform molecular simulations to investigate the interactions in diamond-rock systems. We use nonequilibrium molecular dynamics (NEMD) simulations to explain the increased friction properties observed experimentally at diamond-calcite interfaces compared to diamond-quartz. We consider both dry and aqueous environments using new reactive force field (ReaxFF) parameters, which have been verified against first principles calculations. We monitor mechanochemical processes within these systems such as tip-substrate bond formation and structural changes within both the tip and the substrates. These successfully rationalise the experimentally-observed tribological behaviour.

Session 4A - Tribochemistry II

2:00 - 2:40 pm

3438144: Understanding the In-Situ Formation and Evolution of Phosphorus Antiwear Tribofilms with FFM and NanoIR-AFM
Kerry Cogen, Infineum USA L.P., Linden, NJ, Alison Pawlicki, Matthias Lorenz, Nickolay Borodinov, Olga Ovchinnikova, Oak Ridge National Laboratory, Oak Ridge, TN 

In vehicle transmissions, antiwear tribofilms form from lubricating fluids on rolling / sliding contacting surfaces and serve to control friction and protect surfaces from wear and fatigue. Understanding the mechanism of antiwear film formation and how to tune surface chemistry to control functionality is essential for development of next generation transmission fluids. Here, we developed a unique multimodal AFM methodology to understand initial film formation from different phosphorus-containing lubricants in-situ. We combined Friction Force Microscopy (FFM) to capture the spatial details of friction over the surface as the tribofilm forms and evolves and Nano Infrared Spectroscopy AFM (NanoIR-AFM) to understand the chemistry of the film. We demonstrate the formation of antiwear tribofilms on steel surfaces, the effect of lubricant formulation on how these films evolve in-situ, and the differences in chemistry between these films.

Wednesday, November 11

Session 5B - Surfaces & Interfaces V

9:20 - 10:00 am
3439419: In Situ Study of the Lubrication Mechanism of Phosphonium Phosphate Ionic Liquid in Nanoscale Single-Asperity Sliding Contacts
Filippo Mangolini, Zixuan Li, Oscar Morales-Collazo, Hugo Celio, Andrei Dolocan, Robert Chrostowski, Joan Brennecke, The University of Texas at Austin, Austin, TX, Jerzy Sadowski, Brookhaven National Laboratory, Upton, NY 

Phosphonium phosphate ionic liquids (PP-ILs) have attracted considerable attention in tribology owing to their high thermal stability, good miscibility in hydrocarbon fluids, and excellent lubrication performance. Despite the scientific weight of previous macroscale tribological studies of PP-ILs, a fundamental understanding of the nanoscale lubrication mechanism is still lacking. Here, we used atomic force microscopy (AFM) to evaluate the processes occurring at sliding interfaces in situ, in single-asperity contacts. The AFM experiments, in which a diamond tip was slid on steel in PP-IL, indicated a reduction in friction only after the removal of the native oxide layer from steel. Based on laterally-resolved ex situ analyses of the surface chemistry of steel by X-ray photoemission electron microscopy, low energy electron microscopy, and time-of-flight secondary ion mass spectrometry, a phenomenological model will be proposed to account for the observed tribological behavior.

Session 5C - Tribochemistry III

10:20 - 11:00 am

3482237: Molecules Under Pressure
James Ewen, Hugh Spikes, Tom Reddyhoff, Daniele Dini, Imperial College London, London, United Kingdom

High pressures have wide-ranging effects in tribology, from governing the elastohydrodynamic friction of base oils to driving the mechanochemical decomposition of additives. In this talk, we discuss recent high- pressure studies of friction, wear, rheology, and tribochemistry using molecular simulations and specialised experiments. Recent experiments using the Extreme Traction Machine (ETM) have shown that the mechanochemical decomposition and tribofilm formation of zinc dialkyldithiophosphate (ZDDP) under elastohydrodynamic lubrication (EHL) conditions is due to shear stress, rather than hydrostatic pressure. We also discuss how molecular simulations with accurate all-atom force fields can now provide quantitative agreement with high-pressure viscometer measurements for molecular fluids and their binary mixtures. These simulations not only pave the way for accurate in silico prediction of EHL friction, but also provide unique insights into transport behaviour in the high-pressure, supercooled state. Finally, we discuss molecular fluids that have recently been shown to exhibit macroscale liquid superlubricity under EHL conditions.

Thursday, November 12

Session 7A - Materials Tribology II

10:00 - 10:40 am
3435645: Linking Energy Loss in Soft Adhesion to Surface Roughness

Tevis Jacobs, Abhijeet Gujrati, Subarna Khanal, University of Pittsburgh, Pittsburgh, PA, Siddhesh Dalvi, Ali Dhinojwala, University of Akron, Akron, OH, Lars Pastewka, University of Freiburg, Freiburg, Germany 

A mechanistic understanding of adhesion in soft materials is critical in transportation, biomaterials, and soft robotics. On rough surfaces, the apparent work of adhesion coming into contact is lower than the intrinsic value for the materials, and there is adhesion hysteresis during separation. Still lacking is a quantitative experimentally validated link between adhesion and surface topography. Here, we used in situ measurements of contact size to investigate the adhesion behavior of soft elastic hemispheres on four different nanodiamond substrates with topography characterized down to the Ångström-scale. The results show that the reduction in apparent work of adhesion is equal to the energy required to achieve conformal contact. Further, the energy loss during contact is equal to the product of intrinsic work of adhesion and true contact area. These findings reveal the mechanism that links adhesion hysteresis to roughness, rather than viscoelastic dissipation.

Session 7B - Lubricants III

11:30 am - 12:10 pm
3436105: Optimization of Bio-Derived Basefluid Properties to Improve Efficiency in Hydraulic Systems

Maria Cinta Lorenzo Martin, Oyelayo Ajayi, George Fenske, Argonne National Laboratory, Argonne, IL, Girma Biresaw, Grigor Bantchev, Roger HarryoKuru, USDA, Peoria, IL 

Demand for high efficiency environmentally friendly hydraulic fluids is increasing for a variety of applications, such as agricultural and marine applications. Efficiency of fluid power systems depend on several properties of the hydraulic fluid. The main ones are viscosity (including VI), traction coefficient, bulk modulus, and the boundary friction with appropriate pump and motor materials. Optimization of these properties can provide opportunity for development of efficient hydraulic fluid. Composite fluids consisting of a mixture of PAO and bio-derived ester from high oleic sunflower oil were formulated to have properties similar to commercially available hydraulic fluids. Measurement of the pertinent properties and evaluation of tribological performance indicated the composite fluid has superior or equivalent performance as the current state-of-the-art hydraulic fluids. There are opportunities for further performance enhancement of the composite fluids though formulation.

Session 7C - Machine Elements & Systems I

11:30 am - 12:10 pm

3473456: Use of Tribology in Rolling Bearing Design for Use in Advanced Machinery
Michael Kotzalas, The Timken Company, North Canton, OH 
When people think of the cutting edge of machine design, they often are thinking about electric vehicles, renewable energy or commercial space flight. The last decade has brought about the the beginnings of revolutionary changes in these markets with plug in electric cars or all electric last mile delivery, massive offshore wind turbines, and satellite constellations for global internet and communications coverage. These systems, or the end products that everyone sees, are extraordinary and eye catching, but the design process behind making them work is also highly involved and elegant for those who are knowledgeable in these fields. For the bearing engineer, we must consider new ways of looking at the problems and using tribological theories which allow for the advancements that make these machines work, such as thermal modeling, advanced rheological properties of the fluids, wear testing and material science. Through use of examples, I will discuss how we are implementing these methods into the rolling bearings used in these machines.

Friday November 13

Session 9A - Biotribology

10:20 - 11:00 am
3438863: Tribological and Bactericidal Effect of Nanodiamonds as Potential Lubricants for Artificial Joints
Diana Berman, University of North Texas, Denton, TX

The artificial joints in forms of knee and hip implants are widely used for the treatment of degenerative joint diseases and trauma. Current clinically-used implants, traditionally made from polymer-on-metal structures, often suffer from high friction and wear, leading to associated inflammation and infection resulting in ultimate failure of the artificial joints. Here, we propose an alternative solution to this tribologically-induced failure of the joint materials. We demonstrate that friction and wear behavior of ultra-high-molecular-weight polyethylene (UHMWPE) and titanium tribopair, used to mimic the artificial joint interface, can be improved by introducing nanodiamond (ND) particles in the sliding contact. Analysis of the wear track formed during sliding indicates the formation of a carbon-rich tribolayer of embedded NDs which improves tribological properties of the contacting surfaces and significantly suppressed the wear of the UHMWPE surface. In addition to the improved lubrication characteristics, NDs exhibit high biocompatibility with the bone cells and promising antibacterial properties against S. aureus, the most common strain associated with artificial joint infection. These results indicate that NDs can be used as a promising nontoxic human-body lubricant with anti-wear and antibacterial features, thus demonstrating their great potential to treat artificial joint complications through intra-articular injection.