Seisuke Sakai

Influence of Surface Crack Density on Strength of Ceramics

Bending test specimens made of silicon nitride ceramics were indented with a Knoop pyramid at intervals of 100-5000μm, and four-point bending strength was measured at room temperature. The bending strength increased with decreasing crack interval for the crack interval smaller than 500μm. This was attributed to the interference of stress field around the Knoop cracks. The influence of surface layer removal on the bending strength was studied for the specimens with many surface cracks introduced during the previous machining process. No difference was observed in the bending strength when the surface layer of less than 10μm was removed. This invariability of strength with the surface removal was also attributed to the interference of the stress field.