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Measurement of friction at microscales

TUE : Materials Technology (Mate) group
Publication Date
  • Engineering


poster.dvi Measurement of Friction at Microscales C.P. Hendriks Eindhoven University of Technology, Faculty of Mechanical Engineering Section Materials Technology P.O. Box 513, NL 5600 MB Eindhoven tu Introduction Calculation of friction and wear in engineering applications is still not possible. Investigation on mi- croscopic length scales is neces- sary to quantify the physical pro- cesses which cause friction and wear in sliding contacts. Apparatus A pin-on-plate type apparatus is developed to measure the friction between a micrometer-sized tip and a translating sample. Focus- error detection type optical heads are used to measure the deflec- tions of the leaf springs, which are determined by the friction and normal force on the tip. The nor- mal force is controlled by a piezo- actuator. Further specifications: � load range 1 �N - 100 mN � speed 1 - 1000 �m/s � track length 1 mm Fig.1 Experimental Set-up Results The friction force between single- crystal silicon and a diamond tip strongly depends on the normal force. The same behaviour is ob- served on steel. This is in con- trast with the classical laws of fric- tion, which states that the friction force is proportional to the nor- mal force. Inspection of the wear tracks indicate that the transition is caused by the onset of plas- ticity in the surface layers. Plas- tic deformation of silicon is facili- tated by phase transformation of the diamond cubic structure to an amorphous phase. Fig.2 Friction force between silicon and a diamond tip FEM Simulations Numerical simulations of 2D- sliding contact over a half-plane are performed to support the ex- periments. The first results, ob- tained with elastic-perfectly plas- tic material and zero interfacial friction, show how the friction force is affected by plastic defor- mation of the surface. Fig.3 Results of 2D-numerical sim- ulation Fig4 Plastic strains in a sliding contact Conclusions � Empirical, classical laws of friction do not hold in mi- croscale experimen

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