Multi-scale morphology of diverse particles from CE-5 lunar samples: Implications for flowability of lunar soil

The high-resolution X-ray micro-computed tomography and 3D white light interferometry were first employed to quantify the overall form, local angularity, and surface texture of nine distinct types of Chang’e-5 lunar soil particles. Then the digital particles were generated using the spherical harmonic method, and further incorporated into the discrete element simulations of granular column collapse to explore the flowability of lunar soil and its underlying mechanisms. Experimental results show that monomineral fragments, shaped glasses, polymineral clasts, and agglutinates share similar mean overall regularity values (0.66-0.74), while glass beads exhibit a markedly higher one (0.89), and agglutinates exhibit well-developed internal pores (average porosity: 0.3). Surface roughness varies considerably among distinct types of lunar soil particles. Simulation results show that the particle size governs the macroscopic cohesion of lunar soil by modulating the coordination number. Modal abundance influences the flowability through two mechanisms: large- and medium-scale morphological features affect coordination number, while small-scale surface texture controls interparticle friction. The interparticle adhesive force influences both adhesive strength and coordination number. The combined effects of interparticle adhesion, irregular morphology, and small particle size reduce the flowability of lunar soil. Our simulations further confirm that the critical interparticle adhesion force required to stabilize a lunar soil column with a mean particle size of 67 μm ranges from 2 to 6 nN, which is consistent with the previous back-analyzed or directly-measured results. This study offers important insights into the flowability of lunar soil from the perspectives of particle size, morphology, friction, and adhesion properties.