During cyclic deformation, temperature measurements were carried out with thermocouples. On the basis of the thermoelastic effect, a thermometric method is described which allows the determination of the elastic part of the total deformation. Thus effective stress changes can be determined. The system is quite sensitive and makes it possible to characterize the behavior of a small volume unit during cyclic deformation. The temperature change ,~ T is directly related to the stress change Aa according to Thomson's formula.
Notched AI20 3 specimens were tested under direct tension--compression loading. Cyclic tests with a stepwise load increase were carried out using a tensile tester and a servohydraulic test system. The test frequency was 0.5 and 5 Hz and the stress ratio was R =-1. Load differences and corresponding changes of temperature were measured. By means of the temperature measurements, the notch factor can be determined. It can be shown that the calculated stress concentration in the notched area is much higher than the measured value. This indicates that the stress reduction in A1203 is higher than in non-brittle materials. The predominant mechanism causing reduction of the stress concentration is microcracking.
Fractographic studies with the scanning electron microscope show damage of A1203 under cyclic loading conditions.