ABSTRACT
Cyclic fatigue crack growth behaviour has been investigated in 9 mole % Ce-TZP ceramics with grain sizes varing from 1.1 to 3.0 μm. To ascertain the interaction between crack resistance behaviour and cyclic fatigue crack growth, cyclic fatigue tests were conducted with short double-cantilever-beam (s-DCB) specimens in two conditions: (a) with a sharp precrack without pre-existing 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 factors as low as about 40% of the plateau KI values measured in the R-curves. The size and shape of the t-m transformation zones are different for specimens in R-curve measurements and in cyclic fatigue tests. For the specimens without pre-existing t-m transformation the overall crack growth behaviour can be described by the Paris power law relation: https://www.w3.org/1998/Math/MathML"> da / dN = A Δ K I m https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003421290/07e4de97-c68f-4ca1-95b4-28d8b410031d/content/eq394.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> with m values of 15 for the 1.1 μm grain size and between 8 and 9 for the other materials with larger grain sizes. For the specimens with the preformed transformation zone a “V” shape da/dN versus ΔKI,app relation is obtained. Explanations for these different results in the two conditions are discussed in terms of crack tip shielding effects.
