Effect of Indenter Elastic Modulus on Hertzian Ring Crack Initiation in Silicon Carbide

Hertzian ring cracking in two SiCs was studied as a function of elastic property mismatch between indenter and target. Ring crack initiation forces (RCIF) were measured using ZrO2, steel, Si3N4, Al2O3, and WC balls. The SiCs were similar; however, similar to 20% of the grains in one were larger than the largest grains in the other. Decreasing indenter stiffness resulted in lower RCIFs and initiation occurred at lower forces in the SiC containing larger grains. Using a spherical indenter with similar elastic properties as the target provides a simpler interpretation and useful and confident estimates of ring crack initiation stresses.