Contact Behavior of Lunar Materials and their Simulants: Experimental Observations and Model Developments

The modeling and simulation of lunar surface and sub-surface activities requires an understanding of the mechanical behavior of the regolith and of the terrestrial materials used to simulate its various components. The discrete element method is frequently applied to model regolith mechanics and this approach requires realistic contact models for the subject materials. In support of this approach, we have conducted grain-to-grain contact experiments on lunar materials and their simulants and herein report on several advancements in this effort. The paper describes a time-based, hereditary integral approach to model anelastic deformation, experimental evidence for nonlinear creep behavior in shear is examined and modeled, and the contact behavior of two lunar materials (plagioclase and pyroxene) are compared to that of their terrestrial simulants. Although as demonstrated in our previous work, space weathering substantially degrades the contact behavior (e.g., lower stiffness and increased frictional loss) of individual mineral grains, reasonably good agreement is found in the contact behavior of unweathered lunar materials and their simulants.