Cyclic Fatigue Crack Propagation Behavior of 9Ce‐TZP Ceramics with Different Grain Size

Cyclic fatigue crack growth behavior has been investigated in 9 mol% Ce‐TZP ceramics with grain sizes varying from 1.1 to 3.0 μm. To ascertain the interaction between crack resistance curve behavior and cyclic fatigue crack growth, cyclic fatigue tests were conducted with short double‐cantilever‐beam specimens in two conditions: (a) with a sharp precrack without preexisting t‐m transformation and (b) with a sharp crack after R‐curve measurements, i.e., with preformed t‐m transformation in the crack region. Fatigue crack propagation occurs at applied stress intensity factor values as low as about 40% of the K_I,∞ values measured in the R‐curves. The size and shape of the t‐m transformation zones are found to be different for specimens obtained in monotonic loading R‐curve measurements and in cyclic fatigue tests. For the specimens without preexisting t‐m transformation the overall crack growth behavior can be described by the Paris power law relation: da/dN=AδK^m_I with m values of 15 for the 1.1‐μm grain size and between 8 and 9 for the material with larger grain sizes. For the specimens with the preformed transformation zone, a “V”shape da/dN versus ΔK_I relation is obtained. Explanations for these different results in the two conditions are discussed in terms of crack tip shielding effects.