Tribology is the science and engineering of understanding friction, lubrication and wear phenomena for interacting surfaces in relative motion.
The history of humanity's struggle with friction goes back to ancient Egypt. If you carefully watch the mural that transporting a huge stone statue drawn at the era, you can find a man pouring oil at the tip of a sled to reduce friction.
Amazingly, we still do not understand why friction occurs and why wear occur very well, even in the 21st century.
Friction is difficult to study because the contact area is normally hidden from view.
The problem with this research field is that R&D is done without direct evidence, e.g., "We try to find out why friction occurs without observing what happens at the contact area" or "We sell lubricants that happen to be high performance without observing how they work".
Measuring forces and observing the area at micro-nano scale; we have to do them at the same time to clarify the microscopic mechanisms governing friction and wear.
I made MEMS and put it in TEM.
MEMS measures forces F, N, and TEM observe the contact area A.
That's how we get the key physical parameters such as τ, σ (and μ, of course).
I am the first to make detailed observations of the sliding interface of single asperity friction. In other words, I for the first time observed the sliding contact area with atomic resolution while simultaneously measuring the friction and normal forces.
Our results suggested that an amorphous layer was formed on the interface due to the induced sliding actuation, and that the amorphous sliding should be the origin of the friction force.
1. Waiting time Dependency
The static friction force increases when the objects remain in contact. What is happening in the actual contact area during the stationary contact?
In this study, I fabricated MEMS and actuated it in TEM to observe single-asperity friction with atomic resolution.
I beleive TEM images provide direct data showing what's going on at the contact.
The result attempts to elucidate the microscopic mechanisms underlying time-dependent static friction, which is caused by strengthened contact or a growth of the contact area.
2. Material Dependency
When the material changes, so does the friction. But what exactly about the material causes the friction to change?
No one can provide a definitive answer to this simple question.
My experimental setup, which can directly observe the contact area with atomic resolution, will attempt to unravel this long-standing mystery.
3. Temperature Dependency
A temperature dependency will provide significant cue to clarify the origin of friction.
In other words, research on the temperature dependence of interface strength will determine which of the following hypotheses regarding the origin of friction is the best explanation by its temperature dependence: grain boundary sliding, yield stress, fracture energy, stacking fault energy, or Peirce stress etc....
We will integrate a micro heater in a MEMS device to know the interfacial strength depending on the temperature.
