Effect of the experimental technique onto R dependence of DKth

An experimental study on two structural steels (normalized C45 and 25CrMo4 grades) was conducted to determine the influence of the adopted technique onto the threshold SIF value. For both the tested materials, the standard approach used to pre-crack the specimens showed to have an influence on determining the thresholds, generating SIF higher than the ones estimated adopting compression pre-cracking techniques. This observation can have a huge effect on both life prediction and inspection intervals for a real structure. An example of life prediction was carried out applying the Nasgro equations, with the experimentally estimated parameters, to the propagation of a crack located at the T-transition of a generic railway axle, assumed to be built using the two tested steel grades.