Research

Tribometry and Instrumentation

In Situ Tribology

In situ studies are the state-of-the-art experiments for promoting a mechanistic understanding of complex systems through probing fundamental aspects of a system. Typically, interfacial interactions occur at an interface buried between two solids. This prevents access of traditional microscopy, spectroscopy and other analytical techniques to assess the interfacial interactions (including friction, wear and adhesion). In situ experiments afford the opportunity to make fundamental and mechanistic observations of complex systems (see publications for journal articles and presentations on in situ techniques).

State of the art in situ studies include in situ contacting, adhesion and sliding experiments using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS), electron backscatter diffraction (EBSD) to link material microstructure and its evolution during surface interactions.

In Situ surface interfacial chemistry can be achieved through in situ Raman and surface enhanced Raman spectroscopy (SERS). Molecular scale transfer of solid lubricant materials, including graphite and polymers can be measured after as early as one sliding cycle through in situ surface plasmon resonance (SPR) and surface enhanced Raman spectroscopy (SERS). In situ x-ray photoelectron spectroscopy (XPS) can be used to observe tribochemical changes at sliding interfaces to understand the dynamic, evolving nature of a sliding interface. It is hypothesized that tribochemical reactions occur in polymers, resulting in molecular interactions that are much stronger than what may be predicted by non-reactive simulations. These surface reactions form tribochemically generated transfer films, which dramatically alter the adhesion, friction and wear of the system. Characterization of these new surface chemistries can provide valuable feedback for theoreticians and computationalists doing MD simulations for tribology. A fundamental understanding of these mechanisms could dramatically improve design of materials and mechanical systems.

In Situ Optical Methods: Using in situ optical microscopy and interferometry, we can realize real contact area between randomly rough surfaces with µN force resolution nm scale positioning capabilities. These experiments are used to compare with models of elastomer contact mechanics with collaborator Bo N.J Person at IFF-Institute. Bo is the leading theorists in adhesion and friction of elastomers. This work could dramatically improve the understanding of soft materials such as elastomers and rubbers and significantly alter design strategies for systems like tires, that are responsible for a significant amount of energy loss in automobiles.

Examples of in situ studies

• Friction, wear, contact mechanics and adhesion of elastomers with in situ contact area observation
  • “Optical In Situ Micro Tribometer for Analysis of Real Contact Area for Contact Mechanics, Adhesion, and Sliding Experiments”
  • “Elastic Contact Mechanics: Percolation of the Contact Area and Fluid Squeeze-out”
  • “Adhesion: Role of Bulk Viscoelasticity and Surface Roughness”
• Molecular transfer of polymer composites ith in situ surface plasmon resonance (SPR) and surface enhanced Raman spectroscopy (SERS)
• Environmental sensitivities and tribochemistry with in situ XPS
• Advanced characterization with electron microscopy
• In Situ Thermal Measurement of sliding contacts