PSI - Issue 39

Georg Schnalzger et al. / Procedia Structural Integrity 39 (2022) 313–326 Author name / Structural Integrity Procedia 00 (2019) 000–000

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These examples show that RCF crack propagation as it occurs in tracks, where cracks grow up to tens of millimeters before branching, is experimentally only observed under mixed-mode loads in undeformed materials (Fletcher et al. (2009)). However, the prediction of RCF crack propagation from numerical-based models as proposed by Daves et al. (2019) for example requires pure Mode-I as well as Mode-II FCG data. Therefore, the current work aims to measure the propagation of fatigue cracks in pearlitic rail steels under cyclic Mode-II loading with varying static axial force. In contrast to past research, the focus is on the FCG behavior of different material deformation states in order to determine the influence of shear deformation occurring in the railhead. For this purpose, the pearlitic rail steel is severely deformed prior to the FCG test by a modified version of high pressure torsion (Hohenwarter et al. (2011), Leitner et al. (2018), Leitner et al. (2019)). The paper at first outlines the experimental methodology including the development of a new non-standard FCG experiment and a complementary FEA as well as the pre-deformation method. The results comprise the FCG characteristics in dependence of the material pre-deformation degree with respect to the crack growth rates and macroscopic crack paths. In the discussion, supplementary analyses on microscopic level of the crack path and fracture surfaces are presented to deepen the understanding for the FCG behavior. 2. Methods The test procedure (Fig. 2) is established to investigate FCG in the undeformed and deformed standard pearlitic rail steel R260 under cyclic Mode-II loading.

Fig. 2. Test procedure to investigate Fatigue Crack Growth (FCG) in undeformed and deformed pearlitic rail steel using notched and pre-cracked tubular specimens. Table 1 shows the nominal chemical composition and mechanical properties of the undeformed R260 in the as-rolled condition provided by the rail manufacturer.