Friction and Fracture

Professor Marder is a member of the Center for Nonlinear Dynamics at The University of Texas at Austin. His group’s research is aimed at understanding dynamic fracture, from its atomic-scale underpinnings to its macroscopic implications. They conduct atomistic dynamics simulations on the Lonestar machine at TACC, targeting a range or materials, including plastic, glass, and crystalline silicon. They are directly able to compare the atomic-scale simulations with the macroscopic experiments. In specific studies of the role of friction in fracture, Marder is particularly interested in the atomic-scale behavior of materials in situations where friction is overcome by an applied sliding force.

In some recent experiments, when a sliding force is exerted on one block of material moving over another, "detachment fronts," lines where contact between the materials is broken, move out from the region where the force is applied toward the farthest points from that region. The nominal speed at which such a front moves is the speed of sound across the material, but fronts move slower than this at the start of such a process, then reach the sound speed, when they can ultimately, and surprisingly, "spawn" two further fronts, one supersonic and one subsonic. Marder's simulations of friction in fractures are attempts to explore this behavior further, taking into account surface roughness and temperature. Results from these calculations may have broad application in everything from the problem of keeping nanomachinery going without lubrication to assessing the geophysical friction and fracture behaviors that result in earthquakes.