Although the enormous progress in fatigue investigations and the understanding achieved during the last years, fatigue phenomenon stays as an important problem concerning strength of metals, their life and structural integrity of engineering constructions. One method which is very useful, informative and easy for application is that of investigation of short fatigue-crack growth by replica monitoring of surface crack propagation from the initiation to failure. In our case, this method includes short-crack rotation-bending (R-B) experiments and length measuring of propagating crack
at some cycles
on smooth hour-glass specimens subjected to different frequency and symmetric cycling loading, Table 1. Material under investigation is a rolled lowcarbon, low alloyed steel (RLCLAS), mostly used for off-shore applications and in shipbuilding, marked as 092 according to the Bulgarian Construction Steel Standard. Experimental conditions under in-air R-B are the following: specimen 1 (Stress range, MPa — 620, Frequency
, Hz — 11), and respectively: specimen 2 (620, 11), specimen 3 (580, 11), specimen 4 (620, 6.6).