Physics Colloquium: Friction is Fracture: The onset of frictional motion

Abstract:

I will describe laboratory experiments on the frictional slip along a rough and spatially extended interface. Utilizing simultaneous measurements of the real area of contact together with measurements of the spatial profile of the stresses adjacent to the interface, we perform real-time observations of how interface ruptures that lead to slip events take place. We will present real-time observations of the how slip is born. We observe distinct modes of interface rupture and relate their propagation velocity to stresses along the interface that exist prior to rupture nucleation. These include ruptures that are limited by the Rayleigh wave speed of the material, supershear ruptures and slow rupture fronts that propagate at velocities that are nearly two orders of magnitude more slowly. These modes should be akin to different types of earthquakes that occur along natural faults. 

We will present measurements of the structure of the singular stress fields that surround rupture tips while they are propagating. We will show that many features of these fields can be quantitatively described by classic fracture mechanical solutions describing shear fracture – hence friction is really fracture. 

Event Organiser: Prof. Sasha Gerber