What is it about?
This paper describes how tiny amounts of slip on the rough frictional interface between rock samples control the increase in friction during periods of (nearly) no motion. This goes against the decades-old notion that increase in real contact area, and not slip, on these microscopically rough surfaces determines changes in frictional strength during periods of no slip.
Photo by Marco Reyes on Unsplash
Why is it important?
The strengthening of frictional interfaces during periods of reduced motion control the dynamics of stick-slip instabilities across most materials, including geological faults and their ability to host repeated earthquakes. The most widely used constitutive equation for friction used to model systems ranging from lubricants, micromachines to earthquake nucleation considers frictional strengthening to be insensitive to slip. We not only show that this constitutive equation has little experimental support, but also show that friction evolves dominantly with slip across more than 5 orders of magnitude variations in slip rate.
Read the Original
This page is a summary of: The evolution of rock friction is more sensitive to slip than elapsed time, even at near-zero slip rates, Proceedings of the National Academy of Sciences, July 2022, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2119462119.
You can read the full text:
Rock friction experiments reveal remarkable slip-sensitivity of frictional strength
Rock friction experiments on granite samples on a rotary shear apparatus reveal that friction evolution across many orders-of-magnitude variations in slip rate are more consistent with a model that requires some interfacial slip for friction to evolve. This is in contrast to the traditional view that friction evolves with contact area creep.
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