静水圧下におけるアルミナセラミックスの円筒内圧負荷による破壊

抄録

In the previous paper the fracture criterion of alumina ceramics subjected to triaxial stresses had been examined by carrying out bending tests under various hydrostatic pressures. By considering that in bending the effect of surface crack on fracture would be remarkable and that of non-uniform stress distribution produced in the material was probable, it was concluded that the specimen should be tested under a uniform stress state as possible. In this paper, the material was fractured by applying internal pressure to a thin-walled tubular specimen with open ends under hydrostatic pressure. The fracture criterion was reexamined by comparing the present experimental results with the results obtained in the previous paper.
(1) The fracture stress plotted in the principal stress space showed a similar tendency to the theoretical results for the fracture criterion obtained by taking account of small cracks in the material, in which the material constants had been decided so as to satisfy the experimental results in bending tests under hydrostatic pressures. Thus, the validity of the assumptions in deriving the theoretical results was confirmed.
(2) The experimentally obtained fracture stress was somewhat lower than the theoretical results. This fact may indicate that the theoretical results include the effect of surface crack or non-uniform stress distribution.
(3) In the fracture criterion, the respective material constants of πK_Ic²/4a and K_Ic/K_IIc were corrected, where K_Ic and K_IIc are the respective fracture toughness values for mode I and mode II, and a is the radius of a penny-shaped crack. The corrected fracture criterion agreed quantitatively with that determined from the experimental results.