Dynamics of Brittle Fracture

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0101030 Marder We will carry out studies in single crystal silicon to find how the speed of a rapidly running crack depends upon loading magnitude, loading mode, crystal plane, orientation, and temperature. The studies will include the first investigations of crystalline fracture at temperatures below 100K. We will also provide careful measurements of the structures left behind the cracks, both on and below the fracture surface. In addition, we will investigate the brittle-ductile transition for polymers, glasses, ionic crystals, and alloys, and study the laws governing crack paths in crystalline and amorphous materials.%%%When airplanes or bridges fail, the culprit is often fracture. Cracks race across solid structures near the speed of sound, ripping them in two. At the same time, fracture underlies many processes used to shape materials, such as cutting, sanding, or polishing. The first motivation to study fracture is therefore to protect engineering structures, and the second is to learn new ways to manipulate and form them. We have been constructing experiments to obtain detailed information on how fracture proceeds under precisely controlled conditions. Our experiments will be performed in single crystals of silicon at temperatures that are 200 degrees C below room temperature. The information from these experiments will tell us how the structure of matter at the atomic scale affects fracture, and will test theories claiming to make predictions about possible atomic effects. As the experiments in silicon are completed, we will broaden our studies to investigate crack motion in other crystalline and glassy materials.