  We advance the modeling of rubble-pile solid bodies by re-examining the tidal
breakup of comet Shoemaker-Levy 9, an event that occurred during a 1.33 Jupiter
radii encounter with that planet in July 1992. Tidal disruption of the comet
nucleus led to a chain of sub-nuclei about 100-1000 m in diameter; these went
on to collide with the planet two years later (Chodas & Yeomans 1996). They
were intensively studied prior to and during the collisions, making SL9 the
best natural benchmark for physical models of small body disruption. For the
first time in the study of this event, we use numerical codes treating
rubble-piles as collections of polyhedra (Korycansky & Asphaug 2009). This
introduces forces of dilatation and friction, and inelastic response. As in our
previous studies (Asphaug & Benz 1994,1996) we conclude that the progenitor
must have been a rubble-pile, and we obtain approximately the same pre-breakup
diameter (about 1.5 km) in our best fits to the data. We find that the
inclusion of realistic fragment shapes leads to grain locking and dilatancy, so
that even in the absence of friction or other dissipation we find that
disruption is overall more difficult than in our spheres-based simulations. We
constrain the comet's bulk density at about 300-400 kg/m^3, half that of our
spheres-based predictions and consistent with recent estimates derived from
spacecraft observations.
