PSI - Issue 39

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A.L. Pinto et al. / Procedia Structural Integrity 39 (2022) 409–418 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Figure 1 – Schematic representation of CDM at the contact trailing edge. Positive angles in the counterclockwise direction. It is worth mentioning that microcrack paths in fretting problems are affected by microstructural features (e.g., grain boundaries and crystallographic orientations) and localized plastic deformation near the surface. It is also noted that the orientation of the microcrack varies as the crack grows away from the contact. However, the average stress/strain quantities used in the CDM are based on homogeneous continuum elasticity assumptions. Accordingly, the critical direction provided by the proposed method should be regarded as an engineering estimate of the average path of a crack of length 2 emanating from the crack initiation site. 3.2. Method 2: Method based on LEFM In the Method 2, crack initiation path is estimated by actually propagating a crack through LEFM concepts, Figure 2. In this case, consider a small crack increment of size Δ with orientation emanating from the contact trailing edge ( = − ). This problem can be solved through FE modelling in order to obtain crack’s stress intensity factors ( and ) over time. Those, on the other hand, can be used to estimate the propagation direction of the next crack increment Δ . In this work, this process is undertaken up to the crack reaches the size of 2 . In this work, the crack propagation increment, Δ , was set to 25 μ m, whereas the initial propagation angle, , was set to 45°. Such angle was chosen since this is the direction that maximizes shear stress amplitude at the contact trailing edge. In this case, one assumes that crack nucleation is governed by the formation of slip bands.

Figure 2 – Schematic representation of Method 2 at the contact trailing edge. Positive angles in the counterclockwise direction.