Near-application testing of ceramics under proportional and non-proportional loading*

Abstract The use of ceramic materials in machine parts with multiaxial and non-proportional stresses requires near-application testing to gather parameters for proper strength and lifetime prediction and to reduce the costly testing of prototypes. Therefore, experimental procedures have been developed for testing ceramic specimens with natural flaws under proportional and non-proportional stresses. Testing rings of different diameter ratios under internal pressure allows the estimation of short-term strength, crack growth parameters and of multiaxial failure criteria even with surfaces in “as-fired”-conditions. Assessment numbers, which quantify the influence of failure criteria on test results, are used to compare different experimental setups regarding their ability to reveal failure criteria. An additional setup allows testing with non-proportional stresses and different load sequences. A cylindrical specimen with a necked-down portion is loaded by alternating torque and compressive force to achieve variable mixed-mode-loading on natural cracks in the necking. Test series with alumina and zirconia are in progress and preliminary results are presented.