PSI - Issue 31

Vera Friederici et al. / Procedia Structural Integrity 31 (2021) 8–14 V. Friederici et al. / Structural Integrity Procedia 00 (2019) 000–000

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XFEM calculations are planned similar to the reversed engineering approach described by Babić et al. (2019). Superposition of the stress intensity factor values due to the residual stresses (as result of induction hardening of the raceway) and the applied load (Božić, Ž., 2018) will be evaluated, too. In the first step of this project results of crack propagation and fatigue strength were evaluated. The results show good agreement with literature, although the experiments are not yet completed. 2. Crack propagation and fatigue strength Test samples of various geometries (see Table 1) as well as samples for metallographic inspection were cut from the core of a slewing bearing ring (4 point contact, diameter of 2.3 m), see Figure 2. The chemical analysis revealed that the 42CrMo4 steel contains 0.44 % carbon. Also all other elements meet the specification according to DIN EN 10083.

Fig. 1. (a) Fracture surface of rotating bending specimen. Indicated initiation site, assumed crack path and residual crack area. (b) Illustration of an S-N-curve. Hypothetical proportions of crack initiation and crack growth phase until failure are shown . The rotating bending specimens were taken in two orientations to determine the possible anisotropic properties of the ring.

Table 1. Overview of the specimen. Sample geometry Sampling orientation

Dimensions Heat treatment condition

Number of samples

Core Transition region Hardened surface Core Transition region Hardened surface

15 15 15

Compact tension (CT) specimen

Axial

58 mm x 60 mm x 25 mm

Rotating bending specimen

Axial / tangential

80 mm, Ø= 5.9 mm

25/32 25/25 23/14

Fig. 2. Site of sampling.

After sampling two heat treatments, to mimic the raceway and the transition region of the bearing were carried out. Samples from core material were used as received. Samples which should resemble the raceway or have a similar microstructure to the transition area (between raceway and core) were heat-treated, with the heat treatment parameters shown in Table 2. The experimental investigation consist of rotating bending test (S-N-curve), fatigue crack propagation test and fracture toughness test. The experiments are not yet completed, so only a selection can be shown here (Fig. 3).