Wear of Fluorapatite Single Crystals: IV. Influence of Sliding Direction on Frictional Behavior and Surface Failure

¹ School of Dentistry and College of Engineering, University of Michigan, Ann Arbor, Michigan 48104, USA

Frictional anisotropy of the basal plane of natural fluorapatite single crystals was observed; the coefficient of friction () in the [2110] direction ( = 0.217) was approximately 12% higher than that in the [0110] direction ( = 0.193). The load at which the ductile-to-brittle transition occurred () was significantly higher in the [2110] direction = 77 gm) than in the [0110] direction = 15 gm). A mechanism is proposed involving the maximum normal stress and probable cleavage planes.