**Influence of Tip Geometry on Nanoscratching**

IA Alhafez and A Brodyanski and M Kopnarski and HM Urbassek, TRIBOLOGY LETTERS, 65 (2017).

DOI: 10.1007/s11249-016-0804-6

Using molecular dynamics simulation, we study the influence of the tip
geometry on indentation and scratching. We focus on the specific case of
an Fe (100) surface scratched in **0 (1) over bar(1) over bar** direction.
Three indenter shapes-spherical, conical and Berkovich-are investigated;
for the cone, the semi-apex angle b is varied systematically. For
conical indenters, we find a clear dependence on the semi-apex angle b:
The friction coefficient decreases strongly with b in agreement with a
simple analytical theory, while the hardness increases. For wider cones,
the dislocation network under the groove increases in complexity. The
pile-up produced outside the groove changes from a frontal to a lateral
rim. The results for the Berkovich pyramid line up excellently with the
cones if the traditional concept of an 'equivalent cone angle' is used.
For the spherical indenter, however, we find deviations; it is not well
described by its 'equivalent cone angle.' The sphere shows a smaller
hardness and a higher friction coefficient than an equivalent cone. This
finding quantifies the difference between blunt and sharp indenters in
scratching.

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