Woodruff School of Mechanical Engineering
COE/Structural Mechanics Seminar
DYNAMIC BEHAVIOR OF GRANULAR MATERIALS
Dr. Tracy J. Vogler
Sandia National Laboratories
Wednesday, April 4, 2012 at 3:00:00 PM
MRDC Building, Room 4211
The dynamic behavior of granular ceramics is being studied through a combination of experiments and simulations. A rich and extremely interesting range of behaviors has been observed in quasi-static experiments on granular materials, but their dynamic behavior is less well understood. Experimentally, we have performed planar impact experiments using a novel stepped fixture to determine the shock response. Shock waves in these distended materials travel at wave speeds much slower than in their fully consolidated form, and the waves themselves are structured and display an interesting scaling relationship between rise time and stress. In addition to these compaction experiments, we are measuring the strength of the granular materials through oblique impact experiments, and we are probing the ultra-high pressure response of the material through high velocity impacts using the Z accelerator. In conjunction with these material characterization experiments, we have developed more complex validation experiments with which to determine the applicability of existing continuum models to multidimensional problems. To improve our understanding of the fundamental behavior of these materials, mesoscale simulations resolving individual grains have been performed using an Eulerian finite-difference code. These simulations do a reasonable job of capturing the macroscopic shock response of the material using material properties from the literature. More importantly, they allow us to better understand propagating waves in granular materials and to determine the sensitivity of the response to various material parameters such as initial porosity, material strength, particle shape, and particle arrangement. A critical distance of many particle diameters is required for the wave to reach a steady state. Some aspects of behavior such as friction and fracture are not captured in these simulations, pointing to the need for improved modeling techniques.
Tracy Vogler received his Ph.D. in Engineering Mechanics from the University of Texas at Austin. Following a post-doc at the Army Research Laboratory, he joined the shock physics group at Sandia National Laboratories. His research involves the study of materials at high impact velocities, strain rates, and pressures through experimental, numerical, and theoretical approaches. His main areas of interest are the behavior of granular materials and the strength of ceramics and metals under such conditions. He has been active in the APS Topical Group on Shock Compression of Condensed Matter co-chairing its biennial conference in 2011 and currently serving as chair-elect of the group.
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