The way things break, or fracture, and the way things slide, or friction, are intimately intertwined, according to Hebrew University of Jerusalem researchers who disproved a 500-year-old theory devised by Leonardo da Vinci. The discovery, which just appeared in the international scientific journal Nature, provides implications for describing the mechanics that leads to earthquakes.
The Italian Renaissance genius, who was among other things an engineer, geologist, painter and sculptor, described over half a millennium ago how rough blocks slide over one another, providing the basis for our understanding of friction to this day. The phenomenon of fracture was always considered to be something totally different.
But research by Prof. Jay Fineberg and his graduate student Ilya Svetlizky at the Hebrew University’s Racah Institute of Physics has proven that the two seemingly disparate processes of fracture and friction are actually connected.
Their findings create a new paradigm that is very different from the da Vinci version, and, according to the researchers, gives us a new understanding of how earthquakes occur.
The two scientists produced artificial earthquakes in their lab that showed the friction caused by the sliding of two contacting blocks can only occur when the connections between the surfaces are first ruptured – that is, fractured or broken – in an orderly, organized process that happens at a speed near to that of sound.
The blocks are connected by interlocking rough contacts that define their interface. For motion to occur, these connections have to be broken. This physical process of breaking is called a fracture process and is described by the theory of crack propagation – meaning that the forces that exist at the front edge of a crack become highly magnified, even if the overall forces being applied are initially quite small.
“The insights gained from our study provide a new paradigm for understanding friction and give us a new, fundamental description of the mechanics and behavior that drive earthquakes, the sliding of two tectonic blocks within natural faults,” said Fineberg. “In this way, we can now understand important processes that are generally hidden kilometers beneath the earth’s surface.”