Abstract
The influence of precracking techniques in the crack growth behavior of yttria‐stabilized tetragonal zirconia polycrystals (Y‐TZP) is investigated. Load‐bridge and cyclic‐compression precracking enhance subsequent tensile crack growth rates, in comparison to results that are found with precracks that are extended under four‐point bending prior to testing. The actual influence of these precracking techniques in the near‐threshold crack growth regime is remarkably different. Although load‐bridge precracking produces a pattern of crack growth fluctuations for stress intensity factors, K, lower than the effective crack‐growth threshold of the material, compression‐fatigue precracks start to propagate under far‐field tensile loads at very fast growth rates and for K values that are slightly higher than the effective threshold. Crack‐tip shielding by tetragonal‐to‐monoclinic transformation develops gradually, influencing the crack growth behavior in Y‐TZP. Proposed fatigue crack growth micromechanisms involve damage accumulation at the crack‐tip region. For Kmax > 3 MPa·m1/2, fatigue crack growth rates are strongly affected by environmental interactions at the crack tip, and postulated fatigue micromechanisms include the cyclic degradation of crack‐tip shielding.
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