THE EXPERIMENTAL-VERIFICATION OF THE SHIELDING EFFECT IN ZIRCONIA

The toughening mechanism of CeO2-stabilized ZrO2 (CeO2-ZrO2) was discussed on the basis of the observation of resistance R curve and the stress intensity factor K-tip at the crack tip. A compression splitting test method, compressing the top of the double cantilever beam specimen, was applied to achieve slow crack growth of CeO2-ZrO2. The laser caustic method was also applied to observe K-tip. The results showed that K infinity was increased with increasing crack extension (R curve behaviour). Crack extension started around K infinity of 3 MPa m(1/2), and K infinity increased to 7 MPa m(1/2), where K infinity became saturated. On the contrary, K-tip exhibited a constant value in the range 2 similar to 3 MPa m(1/2) during the crack extension. From observed K infinity and K-tip, the contribution Delta K of transformation toughening was examined on the basis of the relation K infinity = K-tip + Delta K With these results, the shielding effect, which is the relaxation mechanism of stress concentration at the crack tip, was experimental verified.