Abrasive Properties of Test and Training Site Soils: Relative Hardness of Fine Particle Fraction

The experiment reported here shows that fine soil particles contribute to abrasion, wear and ultimate failure of parachute materials in a manner somewhat analogous to three-body abrasion in metals. The hardness of the particles collected at several test, training and maneuver areas is examined and scaled to known natural materials and commercial abrasives. The geometric diameters of the soil grains that enter and imbed in the fibers are a primary factor for understanding the abrasion mechanism. En the case of cordage abrasion, the fraction of soil grains less than 0.2 mm was dominant within the strands and among the fibers. The particles were applied to designated surface grids on relatively large 3 x 3 to 7 x 7 cm Mohs hardness specimens, glass photographic plates and steel cutting tools. All of the fine particles abraded glass photographic plates, with the exception of a soft, nonmagnetic, black fraction found in Camp Blanding fines. None of the materials scratched corundum, although it was possible to make a few scratches in Topaz with almost all specimens. The general upper limit of hardness was similar to that of quartz, which showed some detectable abrasion by five specimens. Fines from the Riyadh, Saudi Arabia, area easily scratched quartz, and this material is the hardest measured to date.