Free-Roller Versus Fixed-Roller Fixtures in Flexure Testing of Advanced Ceramic Materials

The error associated with strength measurements made with fixed-roller and V-grooved roller figures was studied with a variety of roller and figure material combinations. Both the fixed-roller and the V-grooved fixtures yielded an error in stress of about 4 to 7%. They also exhibited an appreciable amount of load strain hysteresis. Dynamic fatigue testing of 96 wt.% alumina verified the error: the fatigue strength was overestimated by 7 to 9% for the fixed roller configuration. The source of error is exclusively attributed to friction between the rollers and the specimen surface, as verified by previous investigators.