Dynamics of Britttle Fracture

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9802562 Marder This project will study the dyanamics of cracks in brittle materials, using single crystal silicon since it is the best characterized material available, and single crystals of high quality are plentiful and relatively inexpensive. The PIs have developed a set of experimental tools that improve significantly the measurement of cracks in motion. Using these tools they will gather data that characterize brittle fracture of silicon, and show how it is influenced by atomic structure. These tools are 1) a dynamic potential drop method which makes it possible to measure the velocity and location of a crack 120, 000 times in succession at intervals of one twentieth of a microsecond and with accuracy of plus or minus10 meters per second; 2) a loading apparatus capable of applying rigid displacements to a 10 cm long sample with accuracy of 0.1 micron; and 3) X-ray topography to obtain images of subsurface conditions, before and after fracture. The research will measure how the speed of a rapidly running crack in single-crystal silicon depends upon loading magnitude, loading mode, crystal plane, orientation, and temperature. The structures left behind the cracks, both on and below the fracture surface, will also be measured. %%% With a detailed understanding of how running cracks respond to external and atomic-scale structures, several issues can be resolved including how microstructural changes make crack propagation energetically more expensive, and using this insight to reduce the brittleness of materials; and using known correlations between damage structures on or below fracture surfaces with velocity to provide post mortem analysis of fracture velocities. This interdisciplinary project is co-funded by the Ceramics Program of the Division of Materials Research and the Office of Multidisciplinary Activities of the Mathematical and Physical Sciences Directorate. ***