EVALUATION OF DEPTHS OF RESIDUAL FATIGUE CRACKS

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 dept h of the future main fatigue crack has a depth 0.1 mm, no matter of st rain range and (prior austenite) grain size. These results were compar ed with maximal depths of microstructurally short fatigue cracks l(o) (parameter of the Kitagawa-Takahashi diagram) measured by surface repl ication method and published in papers [7], [8], [9], [10] and goad co rrespondence was found. From the comparison it follows that for steels with microstructural unit size up to 20 divided by 30 mu m the maximu m 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.