PSI - Issue 66

Ramdane Boukellif et al. / Procedia Structural Integrity 66 (2024) 55–70 Ramdane Boukellif et al. / Structural Integrity Procedia 00 (2025) 000 – 000

60 6

Fig. 6 shows the shift of the crack flanks and the elastic deformation of the half-plane with surface crack due to contact pressure during the rollover process. In this case, the crack faces move alternately in the Z-direction

Fig. 6. Contact pressure and relative motion between the crack surfaces during crack rollover: (a) Rolling element is located in front of the crack; (b) Rolling element is located on the crack; (c) Rolling element is located behind the crack. 3. Prediction of rolling contact fatigue crack propagation In the investigations regarding the crack paths, three cases were distinguished. In Phase I.1, the crack paths were investigated assuming a semi-infinite plane with an edge crack under pure rolling contact. In phase I.2, the residual stresses were also considered. The aim of Phase I.2 was to investigate the maximum crack growth depth and tendency of crack propagation (into the core or back to the surface) in comparison with the basic variant of Phase I.1. The influence of an additional load (complex load) was investigated in Phase II. Using the measured residual stresses, crack growth simulations were then carried out in the hollow shaft and in the outer ring.

3.1. Phase I.1: Pure Rolling Contact Fatigue (RCF)

3.1.1. Vertical initial crack/ consideration of the friction between the crack flanks In this example, the influence of initial crack length/angle on crack paths and SIFs was investigated. The parameters used are defined in Table 1.

Table 1. Parameters used for the prediction of crack path for the vertical initial crack. Parameters Initial crack length

0.5 mm

Friction coefficient (cylinder/half-plane) Contact pressure Friction coefficient (crack surfaces)

0.15 1500 MPa 0.15

The SIF for the initial crack is shown in Fig. 7(b). The curve shows two extreme values with different signs. These are larger than the threshold value of 150 N/mm 3/2 , which can lead to crack branching. These signs indicate the direction in which the crack will grow. This means that the initial crack could propagate right in roll increment 10 and/or left in roll increment 15. The deflection angles at the first crack extension are about ±70° (Mode II controlled). Here, both cracks are assumed to grow simultaneously into the material (see Fig. 8). The cylinder is at the first extreme value before the crack and at the second extreme value after the crack (see Fig. 7(a)).