A new paradigm on the inherent relationship between friction and fractures has implications for understanding earthquakes
A new study at the Rakah Institute of Physics of the Hebrew University of Jerusalem shows a close relationship between "how things break" and "how things slide on a surface". The research undermines the common separation between these questions which goes back all the way to the days of Leonardo da Vinci.
More than 500 years ago, Leonardo da Vinci described how rough blocks slide on top of each other, which provided the basis for the understanding of friction to this day. The phenomenon of fracture has always been considered something completely different belonging to a different field of research.
A new study by Prof. J. Feinberg and his research student Ilya Svetlitsky, at the Rakah Institute of Physics at the Hebrew University, proves that these two distinct processes of fracture and friction are in fact completely intertwined. The research findings, which appeared in the journal NATURE, create a new paradigm that can provide a new understanding of the occurrence of earthquakes in the world.
Feinberg and Svetlitsky produced "earthquakes in the laboratory" and showed that in order to produce friction between two blocks sliding on each other, a "fracture" must first occur in an organized process that occurs at a speed close to the speed of sound.
How does that happen? When blocks are placed on top of each other, and before any movement can occur, they are connected by interlocking contact points that define the material's language. In order for movement to occur, these interlinked bonds have to break and this physical process is called a fracture process. This process is described by the theory of crack propagation, which states that the stresses (or forces) at the initial edge of a crack increase and intensify greatly as the crack propagates, even if the total forces applied to begin with are quite weak.
"The insights gained in our research provide a new paradigm for understanding friction and give us a new fundamental description of the mechanics responsible for the behavior of earthquakes - the sliding of tectonic plates on top of each other under natural circumstances." says Feinberg. "In this way, we can now understand important processes that often take place in secret, kilometers below the surface."
