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298 results on '"Hector, Louis G."'

103. Origin of static friction and its relationship to adhesion at the atomic scale

Author

Zhang, Qing, Qi, Yue, Hector, Louis G., Jr., Çağin, Tahir, Goddard, William A., III, Zhang, Qing, Qi, Yue, Hector, Louis G., Jr., Çağin, Tahir, and Goddard, William A., III

Abstract

Using atomic scale interfaces consisting of slabs of the same materials, we study the relationship between adhesion and static friction. The work of separation, which is a measure of adhesion, and the spatial variation of the interface potential energy along the sliding direction are computed for both commensurate and incommensurate Al2O3/Al2O3 interfaces, and incommensurate smooth and rough Al/Al interfaces. These values are compared with the predicted static friction stress resulting from constant force and constant velocity molecular dynamics simulations. Simulation results show that static friction is not determined by the absolute value of adhesion. Rather, it is determined by the change of potential energy along the sliding direction.

Published
2007

149. Boundary additive effect on abrasive wear during single asperity plowing of a 3004 aluminum alloy

Author

Opalka, Susanne M., Hector, Louis G., Jr., Schmid, Steven R., Reich, Ronald A., and Epp, June M.

Subjects
Aluminum founding -- Research, Aluminum alloys -- Research, Mechanical wear -- Prevention, Lubrication and lubricants -- Usage, Friction -- Prevention, Science and technology
Abstract

Aluminum forming processes such as rolling, extrusion, and ironing involve the transfer of large loads through a tooling/workpiece interface to plastically deform the workpiece to a desired shape. Sharp tool surface asperities can plow the workpiece and lead to elevated friction and temperatures in the interface with a subsequent increase in abrasive wear debris which in turn degrades the surface aesthetics of the final product. To minimize associated friction and wear levels in aluminum forming processes, a base oil with one or more boundary additives is used as a lubricant. At the present time, however, little is known about the mechanisms by which a given additive influences abrasive wear in an aluminum metal forming interface. In the present work, a series of single asperity plowing experiments on a 3004-O aluminum alloy with selected lubricant components was conducted. Three additives were separately investigated, viz., stearic acid, butyl stearate, and lauryl alcohol. The plowing motion of a pyramidal diamond indentor with a cutting edge oriented in the plowing direction (i.e., a sharp indentor) was controlled with the piezo-electric transducers of an atomic force microscope. The experiments help to provide insight about the interplay between additive reaction with the surface and plowing mechanics. Further insight into this interplay and abrasive wear debris generation was sought, albeit qualitatively, through additional experiments involving a diamond indentor for which no one cutting edge was oriented in the plowing direction (i.e., a blunt indentor). The tests allowed evaluation of the boundary lubricant mechanism and propensity for generating wear debris.

Published
1999

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