A thermal shock test has been carried out to clarify the initiation and growth behaviors of surface micro-cracks, in conjunction with both a penetrant test and ultrasonic technique. For this study, alumina ceramic specimen was heated in an electric furnace and then was plunged into a water tank. The ultrasonic pulse echo technique was used to evaluate the characteristic of variation of Young's modulus due to the increase of thermal shock cycles by measuring the changes of ultrasonic longitudinal and shear wave velocities. The Acoustic Emission (AE) technique was also used to evaluate the correct time when a crack initiated on the surface of ceramic during the thermal shock cycle.
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