Abstract
In this work, we employed a soft-sphere discrete element method with a cohesion implementation to model the dynamical process of sub-km-sized cohesive rubble piles under continuous spinup. The dependencies of the critical spin periods Tc on several material parameters for oblate rubble piles with different diameters were explored. Our simulations show that the interparticle cohesive force can strengthen the bodies as expected, especially for the smaller ones. The simulated results of Tc were fitted with the continuum theory developed by Holsapple (2007), through which we find the interparticle cohesion is proportional to the best-fit bulk cohesion and the ratio shows no dependency on the density. In addition, we find Tc decreases as the density increases in the compressive regime, while the trend reverses when transitioning to the tensile regime. Besides, though a higher friction angle can strengthen the bodies, its influence on Tc is minimized near the separation between the two regimes. Our numerical findings are generally consistent with the continuum theory, except that the latter predicts that Tc should increase as the friction angle increases in the tensile regime, which is contrary to the numerical results. This remarkable difference reminds us to take caution when applying the continuum theory to critically spinning cohesive rubble piles in the tensile regime, especially when dealing with the effect of the friction angle. Finally, we emphasize that the separation between the regimes can be specified by a characteristic period, which is only a function of density for a given shape.