Indentation-Precracking and Double-Torsion Methods for Measuring Fracture Mechanics Parameters in Hot-Pressed Si3N4

The two widely used test methods, the indentation-induced flaw (IIF) and the double-torsion (DT), for measuring fracture mechanics parameters were directly compared using a commercial hot-pressed Si₃N₄. The IIF method is simple for estimating the inherent flaw size of the as-received material and in revealing the qualitative nature of slow crack growth as a function of temperature and strain rate. The critical stress intensity factor, K _ic, for catastrophic failure at 20°C was 3.5 and 4.1 MN/m^3/2 using IIF and DT methods, respectively. Crack velocities can be measured with greater accuracy using the DT method.