Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session T2: Focus Session: Improving Models of Geologic & Planetary Materials |
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Chair: Huirong-Anita Ai, California Institute of Technology Room: Hyatt Regency Constellation C |
Thursday, August 4, 2005 1:00PM - 1:30PM |
T2.00001: Using Mesoscale Computational Investigations to Investigate the Role of Material Heterogeneity in Geologic and Planetary Materials Invited Speaker: The propagation of shock waves through target materials is strongly influenced by the presence of small-scale structure, fractures, physical and chemical heterogeneities. Reverberations behind the shock from the presence of physical heterogeneity have been proposed as a mechanism for transient weakening of target materials [1] as are localized shock effects seen in some meteorites [2]. Pre-existing fractures can also affect melt generation [3]. Recent studies in computational hydrodynamics have attempted to bridge the gap in numerical modeling between the micro-scale and the continuum, the meso-scale. Methods are being devised using shock physics hydrocodes such as CTH and Monte-Carlo-type methods to investigate the shock properties of heterogeneous materials [4] and to compare the results with experiments[5]. Recent numerical experiments at the meso-scale using these statistical methods suggest that heterogeneity at the micro-scale plays a substantial and statistically quantifiable role in the effective shear and fracture strength of rocks [6]. This paper will describe the methodology to determine the shear and fracture strength of heterogeneous materials and apply the method to simulations of large crater formation. References: [1] Melosh, H. J. 1979, J. Geophys. Res. 84, pp. 7513-7520. [2] Walton E.L. {\&} J.G. Spray 2003, Met. Planet. Sci. 38, pp. 1865-1875. [3] Kieffer, S. W. 1971, J. of Geophys. Res., 76, pp. 5449-5473. [4] Crawford, D.A. {\&} O.S. Barnouin-Jha 2004, Abstract {\#}1757, 35$^{th}$ Lunar and Planet. Sci. Conf.. [5]~Barnouin-Jha, et al. 2002, 33$^{rd}$ Lunar and Planet. Sci. Conf., pp. 1738-1739. [6] Crawford, D.A. {\&} O.S. Barnouin-Jha 2004, Abs. {\#}5083, 67$^{th}$ Annual Meteoritical Society Meeting. [Preview Abstract] |
Thursday, August 4, 2005 1:30PM - 1:45PM |
T2.00002: Numerical Modeling of Shock-Induced Damage Beneath Impact Craters Huirong-Anita Ai, Thomas Ahrens The mechanical response of rocks under dynamic loading is a complex yet not very well understood phenomenon due to the difficulty of finding proper strength model for geologic materials. Recently AUTODYN-2D is used to simulate the shock-induced damage in a 20x20x15 cm granite block impacted by a lead bullet at 1.2 km/s and the result is compared with experiment data. The Johnson-Holmquist constitutive model for brittle materials, which describes the deviatoric straining in brittle media such as ceramic, is chosen to represent the shear strength of granite. A tensile crack softening model is coupled to simulate the propagation of radial tensile cracks generated by the principal tensile stress perpendicular to the shock front. The tensile stress is assumed to be equal to the deviatoric stress at radii that experience less than the HEL stress. The simulated deformation is also compared with that using CTH and only the JH model. The latter shows that damage for this shot is overestimated, which can be explained by the incapability of JH model to simulate both deviatoric and tensile cracks inducd in brittle rocks under impact. [Preview Abstract] |
Thursday, August 4, 2005 1:45PM - 2:00PM |
T2.00003: The Behavior of Sand Under Shock-Loading Conditions D.J. Chapman, K. Tsembelis, W.G. Proud The behavior of dry and water-saturated sand has been investigated under the condition of uni-axial strain using the plate impact facility of the Cavendish Laboratory, Cambridge, UK. Unlike previous work, manganin gauges were embedded between Mylar sheets and positioned directly in the sand, to obtain the in-material stress. The results are compared with that in the open literature. [Preview Abstract] |
Thursday, August 4, 2005 2:00PM - 2:15PM |
T2.00004: Post-shock Temperature and Free Surface Velocity Measurements of Basalt Gregory Kennedy, Sarah Stewart, Laurel Senft, Michael Furlanetto, Andy Obst, Jeremy Payton, Achim Seifter Basalt is the most common rock on planetary surfaces. Post-shock temperature and particle velocity measurements provide fundamental information about the effects of impact cratering events on planets, the outcome of collisions between small bodies, and the thermal history of meteorites. A high-speed infrared four-wavelength pyrometer, developed at Los Alamos National Laboratory, is used with customized front end optics at the Harvard Shock Compression Laboratory for concurrent observations of particle velocity (VISAR) and free surface emission from Columbia River flood basalt. Preliminary data at a peak shock pressure of 29 GPa indicate that the free surface includes hot spots, likely due to sub-mm void spaces, within the $\sim $4-mm diameter area of the pyrometry observations. The two long wavelength (3.5 and 4.8 micron) channels record a post-shock temperature between 585 and 610 K, slightly higher than the CTH basalt EOS model. The two short wavelength (1.8 and 2.3 micron) channels record hot spot temperatures $>$700 K. Free surface velocity measurements are lower than predicted by the basalt EOS model. Improvements to the basalt EOS using particle and post-shock temperature data will be discussed. [Preview Abstract] |
Thursday, August 4, 2005 2:15PM - 2:30PM |
T2.00005: A Compaction Model for Highly Porous Silica Powder. P.D. Church, I.G. Cullis, D. Porter, K. Tsembelis This paper describes research to develop an equation of state to describe the behaviour of a highly porous silica powder. It shows that whilst molecular modelling techniques can be readily applied to develop a description of a compact material the description of the compaction process is more problematic. An empirical model, based upon the Lennard-Jones potential, has been shown to be capable of describing the compaction process observed in simple experiments. This development and application of the model in the Eulerian hydrocode GRIM to reproduce experimental plate impact data over a wide range of impact velocities is described and the results compared with experimental data. [Preview Abstract] |
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