Sticky or not sticky? Measurements of the tensile strength of microgranular organic materials

Abstract

ABSTRACT Knowledge of the mechanical properties of protoplanetary and cometary matter is of key importance to better understand the activity of comets and the early stages of planet formation. The tensile strength determines the required pressure to lift off grains, pebbles, and agglomerates from the cometary surface and also describes how much strain a macroscopic body can withstand before material failure occurs. As organic materials are ubiquitous in space, they could have played an important role during the planet-formation process. This work provides new data on the tensile strength of five different microgranular organic materials, namely, humic acid, paraffin, brown coal, charcoal, and graphite. These materials are investigated by the so-called Brazilian Disc Test and the resulting tensile strength values are normalized to a standard grain size and volume filling factor. We find that the tensile strength of these materials ranges over four orders of magnitude. Graphite and paraffin possess tensile strengths much higher than silica, whereas coals have very low tensile-strength values. This work demonstrates that organic materials are not generally stickier than silicates, or water ice, as often believed.