Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session S2a: Granular Impact-Cratering Dynamics and Morphology |
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Sponsoring Units: DCMP Chair: Robert Behringer, Duke University Room: LACC 151 |
Wednesday, March 23, 2005 2:30PM - 3:06PM |
S2a.00001: Dynamics of projectile impact in a two-dimensional granular medium Invited Speaker: Our experiments and molecular dynamics simulations on a projectile impacting a two-dimensional granular medium reveal that the average deceleration of the projectile is constant during the penetration and proportional to the impact velocity [M. Pica Ciamarra, A. H. Lara, A. T. Lee, D. I. Goldman, I. Vishik, and H. L. Swinney, Phys. Rev. Lett. 92, 194301 (2004)]. Thus the time taken for a projectile to decelerate to a stop is independent of its impact velocity. The simulations show that the probability distribution function of forces on grains is time independent during a projectile's deceleration in the medium. At all times the force distribution function decreases exponentially for large forces. [Preview Abstract] |
Wednesday, March 23, 2005 3:06PM - 3:42PM |
S2a.00002: Low-speed impact cratering in loose granular media Invited Speaker: In this talk I shall describe the penetration of projectiles dropped into noncohesive granular media, and how the results vary with the properties of both the projectile and the medium. In contrast to wide assumption, the penetration depth and crater diameter represent two distinct length scales. The diameter scales as the 1/4 power of projectile energy, but curiously the depth is not a simple function of either the projectile energy or momentum at impact. Rather, it scales as the 1/2 power of density, the 2/3 power of projectile diameter, and the 1/3 power of total drop distance. This same result also holds for cylinders with a variety of tips, and so is not an accident of projectile shape. It is crucial to understand the penetration depth because it is directly related to the mechanics of impact, namely the average stopping force acting between projectile and medium. In addition to this discussion, I shall also present new data on the dynamics of impact. All experiments were constructed and carried out at UCLA by undergraduate physics majors: Jun Uehara, Katie Newhall, Chris Santore, and Mike Ambroso.\newline\newline [1] J.S. Uehara, M.A. Ambroso, R.P. Ojha, and D.J. Durian, ``Low-Speed Impact Craters in Loose Granular Media,'' Phys. Rev. Lett. {\bf 90}, 194301 (2003).\newline [2] K.A. Newhall and D.J. Durian, ``Projectile-shape dependence of impact craters in loose granular media,'' Phys. Rev. E {\bf 68}, 06030R (2003).\newline [3] M.A. Ambroso, C.R. Santore, A.R. Abate, and D.J. Durian, ``Penetration depth for shallow impact cratering,'' cond-mat/0411231 (2004). [Preview Abstract] |
Wednesday, March 23, 2005 3:42PM - 4:18PM |
S2a.00003: Simulations of impact cratering in granular media Invited Speaker: We simulate impact cratering in two dimensions using soft particle molecular dynamics simulations. We systematically vary the physical parameters of the grains and the ball (density, size, friction, impact energy). Our results confirm the recently observed scaling of the crater depth with impact energy as observed by Uehara et al and the effect of constant deceleration of the ball during the penetration phase as observed by Pica Ciamarra et al. We focus on the distribution of energy dissipation during the impact among various dissipation mechanisms and conclude that the most significant dissipation occurs due to internal frictional contacts among the grains. [Preview Abstract] |
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