Cracks and Shocks

Professor Marder is a member of the Center for Nonlinear Dynamics at The University of Texas at Austin. The goal of their research into fracture is to study material fracture as a dynamical system, to understand how dynamics at small (atomic) scales emerges as phenomena observable at the macroscopic scale. Puzzles arise in this field because the speed at which a crack (fracture) in a material propagates is often much, much slower in experiments than calculated in most theories. Marder studies fracture in brittle, amorphous materials like Plexiglas, in glass, and in structured materials like crystalline silicon. He and his group have developed complete analytical solutions for the fracture behavior of crystals, for use in comparison with laboratory experiments and simulations. Their molecular dynamics code, which they run on the Lonestar machine at TACC, is specially suited to studying the fracture of materials with three-body interactions.

One useful feature of the fracture code is that it has the ability to focus on the atoms in the vicinity of a traveling crack tip, pasting new material on the front, and discarding material from behind as it becomes irrelevant. The group has now developed a similar technique to study shocks, so they can follow the dynamics of a shock wave for a long time with minimal computational cost. Applying this method to shocks involves establishing appropriate thermodynamic conditions at the front and the back of the sample.