セラミックスの熱衝撃疲労におけるき裂進展挙動

抄録

Thermal shock fatigue experiments were carried out on notched Al₂O₃ ceramic specimens by using a water quench technique. The crack growth behavior from initial cracks, which were introduced by thermal shock at the notch root or Vicker's indentation or on the surface of specimens, was studied. Each crack grew and finally branched under a repetition of thermal shock. In this study, the crack growth behavior before the branching was mainly investigated. The results showed that the crack growth rate was reduced with an increase of the number of thermal shock regardless of initial crack size and thermal conditions. When a relatively higher temperature difference was repeated, a crack grew discontinuously and finally stopped. Such a crack growth behavior suggests that some damage occured at a crack tip under a repetation of thermal shock. In order to consider these behaviors, steady-state thermal stress was analyzed by FEM. In this result, the crack opening stress at a crack tip near the surface increased at first and decreased with an increase of crack length after the maximum stress value. In order to show the damage produced at a crack tip by thermal shock fatigue, the bending strength was evaluated after the repetition of thermal shock. After the repetition of a smaller thermal shock, no crack was observed but the bending strength was reduced.