Indentation crack profiles in silicon nitride

Indentation crack profiles that form under Vickers and Knoop indentations in silicon nitride were investigated. Two different experimental techniques were used to obtain a complete representation of the radial/median as well as the lateral crack system and the plastic deformation zone as a function of indentation load. Vickers indentation cracks exhibit a load dependent shape. At low loads two seperate radial cracks form per median plane, at high loads these cracks merge beneath the hardness impression to form an annular crack. Lateral cracks appear much closer to the surface than frequently assumed. Knoop cracks are nearly semielliptical. The crack aspect ratio and the aspect ratio of the elongated wedge-shaped plastic deformation zone are load dependent.