We used granular mechanics simulations to study collisions between spherical aggregates and axisymmetric ellipsoidal aggregates of equal mass. Non-spherical aggregates may be generated, for example, as the result of previous aggregate collisions, either from the merging of aggregates or from fragmentation processes. Of particular interest is the growth velocity, i.e., the critical collision velocity above which the size of the largest post-collision fragment is smaller than the original aggregate size. We find a systematic decrease of the growth velocity with axis ratio of the ellipsoid. The decrease is caused by the ‘rim peel-off’ effect: grain material close to the rims is more readily ejected from the boundaries of aggregates. When considering collisions with ellipsoids of identical semi-major axis, the growth velocity of oblate ellipsoids surpasses that of prolate ellipsoids. Averaging over the orientation of the ellipsoid and over the impact parameters possible in a collision retains the above-mentioned results. The influence of aggregate shape on collision outcomes is of interest, for instance, for codes describing the evolution of dust clouds under collisions.
Collisions between granular aggregates influence the size distribution of dust clouds. Granular aggregates may possess non-spherical shapes as a result of, for instance, previous collision processes. Here, we study aggregate collisions using a granular mechanics simulation code. Collisions between spherical aggregates are compared to collisions of ellipsoidal aggregates of equal mass. As the most prominent result, we find that the growth velocity, i.e., the velocity above which the post-collision aggregates are smaller than before collision, is generally reduced for ellipsoidal aggregates. The reason hereto lies in the less compact structure of ellipsoids which allows for a larger degree of fragmentation in a ‘rim peel-off’ mechanism. On the other hand, relative fragment distributions are only little influenced by aggregate shape.
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