Abstract: The effects of control mode and rate on the fracture toughness of ceramics were measured by using chevron-notched flexure specimen in accordance with ASTM C1421. The use of stroke control gave consistent results with about 2% variation in measured fracture toughness for a very wide range of rates (0.005 to 0.5 mm/min). Use of strain or CMOD control gave ~5% variation over a very wide range of rates, with the measurements being a function of rate. However, the effect was eliminated by use of d…