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In this work, we employ a soft-sphere discrete element method with a cohesionimplementation to model the dynamical process of sub-km-sized cohesive rubblepiles under continuous spinup. The dependencies of critical spin periods $T_c$on several material parameters for oblate rubble piles with different bulkdiameters $D$ are explored. Our numerical simulations show that both theincrease of interparticle cohesion and particle shape parameter in our modelcan strengthen the bodies, especially for the smaller ones. In addition, wefind there exists some critical diameter $D_{cri,\rho}$ at which the variationtrend of $T_c$ with the bulk density $\rho$ reverses. Though a greater staticfriction coefficient $\mu_S$ can strengthen the body, this effect attains aminimum at a critical diameter $D_{cri,\phi}$ close to $D_{cri,\rho}$. Thecontinuum theory (analytical method) is used for comparison and two equivalentcritical diameters are obtained. The numerical results were fitted with theanalytical method and the ratio of the interparticle cohesion $c$ to the bulkcohesion $C$ is estimated to be roughly 88.3. We find this ratio keeps constantfor different $c$ and $\rho$, while it strongly depends on the friction angle$\phi$. Also, our numerical results further show that the dependency of $T_c$on $\phi$ is opposite from that predicted by the continuum theory when $D$ <$D_{cri,\phi}$. Finally, we find that the two critical diameters happen to beclose to the diameter when the mean normal stress of the body equals zero,which is the separation between the compressive regime and the tensile regime.

Critical spin periods of sub-km-sized cohesive rubble-pile asteroids: dependencies on material parameters