Using Mesoscale Computational Investigations to Investigate the Role of Material Heterogeneity in Geologic and Planetary Materials

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.