Griffith Theory Applied to Dust Lofting on the Moon

Details Griffith Theory Applied to Dust Lofting on the Moon Griffith Theory Applied to Dust Lofting on the Moon

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p32a..07m&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P32A-07

Other

[5400] Planetary Sciences: Solid Surface Planets, [6250] Planetary Sciences: Solar System Objects / Moon

Scientific paper

Griffith Theory is normally applied to strong solids to explain their breakage at stress levels well below theoretical strength. The theory is based on the fact that most brittle solids have surface flaws (microcracks, lattice dislocations, etc). When a solid is subjected to a physical stress field, the stress finds the weakest (critical) flaw and initiates fracture at this stress-riser; solids do not break at the theoretical strength dictated by intermolecular forces. Griffith theory can be applied to weak solids such as cohesive powders of which the lunar regolith is an example. Uncompressed powders have non-uniform packing, often with frequent voids, a reflection of the relationship between grain shape, emplacement history, and the ratio of grain weight to interparticle (e.g. vdW) forces. The result is great variation in powder strength from one place to another within the powder bulk. If a powder is subjected to Coulombic stress due to static charging, it will fail at a stress-riser such as a void, rather than at a junction between two of the powder’s smallest particles (which are equivalent to molecules in a strong solid). In experiments in which simulant lunar regolith was subjected to Coulombic stress by tribocharging and also by electron-beam charging in an SEM, it was found that aggregates of 10 E2 to 10 E6 particles would be lofted from the powder surface in preference to micron or submicron particles which remained steadfastly attached to larger host grains. The same observation was made in experiments involving the application of pneumatic stress to the simulants. The application of Griffith Theory to powders is borne out well by experiments. For the Moon, it might be inferred that there is a preference for aggregates to be lifted rather than submicron particles. If the latter are lifted at all, they might only form a miniscule fraction of the mass of material potentially in electrostatic entrainment close to the lunar surface.

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