PSI - Issue 13

H. Soares et al. / Procedia Structural Integrity 13 (2018) 1786–1791 Soares et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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been shown that fatigue in metals may occur in any range of cycles, even beyond what was once considered the fatigue life limit, therefore fatigue characterization of structural materials in all load ranges continues to be a challenge, Bathias (1999). In this work, a railway wheel material is under evaluation using multiaxial fatigue testing to perceive its response on the high cycle fatigue (HCF) regime, under multiaxial loading conditions. The experiments were conducted using a servo-hydraulic machine with standardized specimens. All the material samples were machined from a single worn-out railway wheel.

2. Materials and Methods

The component in study is a worn-out railway wheel that should follow the EN_13262+A1-2009 standard. The machine used in the multiaxial fatigue experiments was an Instron 8874 equipped with a 25 kN and 100 N.m load cell. All specimens were machined directly form the railway wheel from specific locations as shown in Figure 1. The specimen geometry and its dimensions are presented in Figure 2.

Fig. 1. Representation of the specimen’s location on the railway whe el.

Fig. 2. Conventional high cycle fatigue specimen that follows the ASTM E606 (2003) standard (mm).

Three types of loads were applied; Case 1 (uniaxial loading in tension), Case 2 (proportional), and Case 3 (non proportional – 90º phase shift). The corresponding loading paths are shown in Figure 3. All tests were conducted with a 5 Hz frequency. Runouts where considered at 1E06 cycles, meaning that if a given specimen reached such number of cycles, a new specimen is introduced, and higher stresses are applied.

Fig. 3. Loading cases. Case 1 – normal uniaxial loading, Case 2 – proportional loading, Case 3 – out-of-phase loading.

3. Theoretical 3.1. Critical plane models

Critical plane models are suitable to estimate crack initiation planes. The most used are the Brown-Miller, Findely, Fatemi & Socie, Liu I, Liu II and SWT, Fatemi and Socie (1988). These models use a constant damage scale between normal and shear loads to estimate critical planes and estimate fatigue lives. In this study, the influence of heat treatment in the crack initiation plane is analyzed by correlating the critical plane estimates with the experimental crack initiation planes.