Papers by Keyword: Maincrack Formation

Abstract: A new experimental technique, Disc-on-Rod test, was developed for evaluating the thermal shock fracture characteristics of ceramic materials. The specimen is disc shaped with a diameter of 20 mm and a thickness of 0.6 mm, and the 2-dimensional thermal stress field was obtained. The specimen was heated to a high temperature and the center region was quenched by means of contact with a cool metal rod with a diameter of 4 mm. The temperature distribution of the specimen was measured by a high speed IR camera and used for the determination of the thermal stress field in the specimen using FEM calculations. In order to evaluate the fracture process, AE signals during thermal shock fracture were detected. It was observed that the maincrack was initiated at the center region, which was subjected to the maximum balanced biaxial stress. The critical stress for maincrack formation was evaluated and compared with that under mechanical loading, considering the volume effect of strength based on Weibull statistics.

Abstract: Microfracture process during bending tests of alumina ceramics used for artificial joints was evaluated by acoustic emission (AE) technique. Four-point bending tests were carried out in air, refined water, physiological saline and simulated body fluid. AE behavior during bending test inhibited the rapid increasing point of AE events and energy prior to the final unstable fracture. It was understood that the bending stress at the increasing point corresponds to the critical stress for maincrack formation. The critical stress was affected by water in environments more strongly than fracture strength. Consequently, it was suggested that the characterization of maincrack formation is essential for the long-term reliability assessment of load-bearing bioceramics.