On the Behavior of Granular Materials in Rough Wheel Contacts on Mars

The extremely remote location of Mars suggests that it is not possible to carry enough flight resources to make a roundtrip. Therefore, in-situ mining, conveyance, and transporting of Martian soil must be conducted with the aid of wheel-based vehicles. However, there is limited understanding of the behavior of granular materials in rough rolling contacts with prescribed wheel roughness (or traction). On earth, rolling contacts in the presence of liquid surfaces oftentimes exhibit boundary-traction and hydrodynamic slip, where accurate prediction of the traction behavior between the wheel and the surface is governed by dry friction and hydrodynamic theory. Since granular materials have been known to behave as solids and liquids, a predictive modeling framework is needed to study the behavior of these complex materials under load and as a function of wheel roughness in interfaces. This work describes the usefulness of employing a tribology-based continuum modeling approach, known as granular kinetic lubrication (GKL), to model granular flows in a rough and fixed-load parallel shear cell. Additionally, a lattice, rule-based mathematics modeling approach, known as cellular automata, is explored as a more simplified tool for modeling complex granular systems in shear cells. Results from the two modeling approaches are compared and comments about their usefulness in advancing an understanding of vehicle transport on Martian regolith are made. Lastly, preliminary experimental results are presented on granular flows with varying wheel roughness.