DEFORMATION OF SAPPHIRE INDUCED BY A SPHERICAL INDENTATION ON THE (10(1)OVER-BAR0) PLANE

This work clarifies the origin of the characteristic discontinuities r egistered during the deformation of the <(10(1)over bar 0)> plane of s apphire, by means of depth sensing indentation experiments with a sphe rical indenter. The sudden increase of the plasticity of the crystal w as found to be caused by a twinning process, The calculation and analy sis of the distribution of resolved shear stresses under a spherical i ndenter predicted the features of the surface deformation. The high re solution microscopic examination of the residual impressions confirmed the theoretical prediction. (C) 1996 American Institute of Physics.