Influence of porosity on collisions between dust aggregates

Abstract

Context. Collisions between dust particles may lead to agglomerate growth or fragmentation, depending on the porosity of the dust and the collision velocity.Aims. We study the effect of agglomerate porosity and collision velocity on aggregate fragmentation and agglomeration.Methods. Granular-mechanics simulations are used to study the outcome of head-on dust aggregate collisions. The aggregates are composed of silica grains of 0.76 μ m radius and have filling factors of between 0.08 and 0.21. The simulations incorporate repulsive and viscoelastic, dissipative normal forces, and intergrain adhesion. The tangential forces are composed of gliding, rolling, and torsional friction. To study the effect of aggregate porosity, we prepared spherical aggregates with identical radius but differing particle numbers. Results. The threshold velocity for agglomerate fragmentation decreases with the porosity of the aggregates. Porous aggregates tend to fragment more easily, and the fragments are irregularly shaped. In the agglomeration regime, the merged aggregate is more compact than the initial collision partners. The collision velocity at which compaction is highest is independent of the initial porosity.