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Normal and sliding contact experiments on gneiss

Content Provider	Springer Nature Link
Author	Cole, David M. Mathisen, Lillian Uthus Hopkins, M. A. Knapp, Byron R.
Copyright Year	2010
Abstract	The development of reliable discrete element models to simulate the mechanics of granular media requires knowledge of the grain-to-grain contact laws of the material in question. We have conducted a series of normal and sliding contact experiments on material used in laboratory triaxial experiments to obtain such contact laws for DEM simulations of the experiments. The contact experiments employed segments of 14.72 mm-diameter spherical grains from the triaxial specimens and flat specimens of the same material. The spherical grains had a uniform diameter with a smooth surface finish. Monotonic and cyclic loading paths were applied in both the normal and sliding modes, and both sphere-sphere and sphere-flat contact behavior were examined. Force-displacement behavior and frictional loss were measured in all cases. The behavior was generally Hertzian in the normal contact experiments, which involved forces up to approximately 100 N. The normal contact stiffness increased from ≈2 to 15MN m−1 over the range of normal force examined. The sliding experiments employed several normal forces up to approximately 25 N, and produced a value of the coefficient of static friction of 0.28. The shear stiffness of the sliding contact increased with normal force, and ranged from 0.8 to 1.2MN m−1 under normal loads ranging from ≈1 to 7.5 N, respectively, for virgin contacts. The shear stiffness observed for the sphere-flat contact decreased with wear. Surface roughness measurements were obtained on both tested and untested regions of the spheres and flat specimens. The average roughness (Ra) for untested regions of the sphere and flat specimens were 270 and 230 nm, respectively. Repeated testing in the sliding mode reduced these values by 29–45% for the flat surfaces, and by 20% for the spherical contact. Frictional losses were observed in both the normal and sliding modes. In the sliding mode, frictional loss decreased with increasing normal load. We observed stable sliding (associated with significant contact movement under an increasing shear force) at forces that were below the macroscopic frictional limit and resulted in permanent displacement of the contact. There was generally a distinct threshold in shear force for this permanent sliding. The extent of sliding increased significantly with wear for the sphere-flat contact and was accompanied by a substantial drop in shear stiffness.
Starting Page	69
Ending Page	86
Page Count	18
File Format	PDF
ISSN	14345021
Journal	Granular Matter
Volume Number	12
Issue Number	1
e-ISSN	14347636
Language	English
Publisher	Springer-Verlag
Publisher Date	2010-01-29
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Contact mechanics Contact stiffness Gneiss Experiments Micromechanics Engineering Thermodynamics, Heat and Mass Transfer Industrial Chemistry/Chemical Engineering Geoengineering, Foundations, Hydraulics Materials Science Engineering Fluid Dynamics Soft and Granular Matter, Complex Fluids and Microfluidics
Content Type	Text
Resource Type	Article
Subject	Physics and Astronomy Mechanics of Materials Materials Science

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