Approximately 100 million terajoules, is used annually just to

Approximately one fifth of
all energy produced worldwide, about 100 million terajoules, is used annually
just to overcome friction in everything from ceiling fans to automotive
industries. Friction reduction can have important implications for reducing energy loss and increasing
the lifetime of devices. Up to now, improvements in lubricants, engineered
surfaces, and mechanical design have led to progress in reducing friction;
however, many fundamental questions in the field of tribology remained
unanswered. For instance, the basic mechanism and effect of the extreme temperatures
on friction at atomic scale is not yet fully understood. High temperature friction is relevant to many
applications that either operate in elevated temperature environments or are
designed to manage temperature rise. The temperature dependence of friction is
also important in aerospace systems such as satellites, which possess thousands
of moving, contacting parts exposed to temperatures ranging from a few hundred
degrees Celsius down to near absolute zero, but cannot be serviced once
deployed in space and so must not fail. Understanding, predicting, and
controlling friction as a function of temperature is therefore critical. The
proposed research is focused on mechanisms that determine the temperature dependence
of friction for nanoscale single asperities. This work can ultimately
contribute to a deeper understanding and more precise and predictive approach
to designing reliable, energy-efficient systems.
The intellectual merit of this research lies in advancing the
fundamental understanding of the temperature dependence of friction for single
asperities. Atomistic simulations and atomic force microscopy experiments will
be conducted, where state-of-the-art methods are used so that the conditions in
the simulations and experiments are optimally matched, allowing results to be
directly compared and validated, maximizing the understanding gained. This
tightly-coupled approach will enable the atomic structure, mechanics, dynamics,
and thermal behavior of the contact to be deterministically linked with
friction forces and the corresponding energy dissipation. Key features of the
proposed unique collaborative approach are: integration of advanced
variable-temperature atomic force microscope measurements and atomistic
simulations of optimally-matched systems; use of novel thermal probes that
enable rapid variation the temperature of the contact; and modeling and
simulation at the same sliding speeds through the use of accelerated
simulations and ultrafast atomic force microscope scanning. With this
comprehensive approach, the underlying mechanisms governing the temperature
dependence of interfacial friction can be definitively established.