Issue 37

J. Vázquez et alii, Frattura ed Integrità Strutturale, 37 (2016) 38-45; DOI: 10.3221/IGF-ESIS.37.06 41 the crack advances 1 µm in this direction, (point 2 in Fig. 5). Then at point 2, again the critical plane is determined and a new 1 µm increment of crack length in this direction is assumed, leading to a new point 3. Repeating again and again this procedure a crack path is obtained. This procedure is not orthodox since this is not the way a crack propagates but, nevertheless, it is interesting to see the results and compare them with the other alternatives. Figure 4 : Crack profile at: a) crack 1, b) crack 2 and c) crack 3. Fig. 6 shows, in addition to the averaged paths for the experimentally observed cracks, the paths obtained with this procedure. First, note that FS parameter, although being the most suitable fatigue parameter for fretting -it combines both shear and normal stresses and would therefore predict better the experimentally observed initiated cracks- produces the worst results, i.e., the predicted crack path grows outside the region beneath the contact zone. On the other hand, the SWT parameter predicts a crack path growing into the region beneath the contact zone, similar to the one obtained experimentally. It is important to recall that the FS parameter and, therefore, the critical plane orientation, depend on the value considered for the k parameter. This parameter, k , measures the relative importance of the stress normal to the crack plane in the Fatemi-Socie criterium. Nevertheless, the results are very similar even when varying the value of k from 0.44 [[12]] –being this value used for the path shown in Fig. 3– up to an exaggerated value of 100.