Abstract
A statistical evaluation of depths of physically short fatigue cracks, residual in LCF test specimen, tested previously at strain range from 0.5 to 5% is described. From evaluation it follows, that minimal depth of the future main fatigue crack has a depth 0.1 mm, no matter of strain range and (prior austenite) grain size. These results were compared with maximal depths of microstructurally short fatigue cracks l_o (parameter of the Kitagawa-Takahashi diagram) measured by surface replication method and published in papers [7], [8], [9], [10] and good correspondence was found. From the comparison it follows that for steels with microstructural unit size up to 20-30 µm the maximum depth of microstructurally short semicircular fatigue crack l_o may be found by evaluation of cracks depths, residual in broken specimens after low cycle, constant strain range fatigue tests.

Key words
statistical evaluation, short fatigue cracks, LCF test, fatigue cracks

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