Different procedures are available to determine the subcritical crack growth behavior of natural cracks in ceramic materials. In order to compare the results obtained from different methods, dynamic bending tests [1] and lifetime tests under constant load were performed. A commercial alumina, Frialit F99.7 (Friatec, Friedrichsfeld), with a median grain size of d_m ≈ 9 μm was tested. Its surface treatment resulted in the roughness parameters: arithmetic surface roughness R_a = 0.7 μm, reduced peak height R_(pk) = 0.3 μm, core roughness depth R_k = 1.6 μm, reduced valley depth R_(vk) = 1.7 μm.
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