PSI - Issue 66

Andrea Zanichelli et al. / Procedia Structural Integrity 66 (2024) 471–477 Author name / Structural Integrity Procedia 00 (2025) 000–000

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Table 2. Experimental tests considered (Araújo et al. (2004)): radius of the pads, R , constant normal load, P , amplitude of the alternating cyclic tangential load, Q a , amplitude of the alternating cyclic axial stress, , B a  , and fatigue life, N f,exp . Group No. Test No. R [mm] P [N/mm] Q a [N/mm] , B a  [MPa] N f,exp [cycles] 1 T1 50 93 42 92.7 1.29E+06 T2 75 140 63 6.70E+05 T3 100 186 84 8.50E+05 T4 125 233 105 7.30E+05 T5 150 280 126 6.70E+05 2 T6 37.5 58 26 92.7 4.04E+06 T7 50 77 35 1.50E+06 T8 75 116 52 8.00E+05 T9 100 155 70 6.10E+05 T10 125 193 87 1.24E+06 T11 150 232 104 6.90E+05 3 T12 75 116 52 77.2 1.42E+06 T13 100 155 70 6.10E+05 T14 125 193 87 1.24E+06 4 T15 125 136 61 61.8 1.57E+06 T16 150 163 74 1.23E+06 Four groups of experimental tests characterised by different fretting loading conditions were tested and, for each group, different values of the radius of the cylindrical pads were adopted (Table 2). The fretting loading conditions were those typical of classical fretting fatigue testing (i.e. a constant normal load, and a cyclic tangential load in phase with a cyclic axial load), and are summarised in Table 2. The experimental fatigue life for each tested specimen is listed in Table 2. Moreover, experimental cracks were found to nucleate around the contact edge, directed toward the centre of the contact, with an orientation (defined with respect to the perpendicular to the contact surface) ranging from 18° to 32°, for the first few hundred microns. Then, the main crack further propagated almost perpendicular to the surface. 4. Results and discussion The experimental campaign detailed in Section 3 is simulated by means of the methodology described in Section 2, and the results obtained are reported and discussed hereafter. In terms of fatigue life, the comparison between analytical estimations and experimental findings is shown in Figure 1. Note that the dashed lines indicate scatter band 2 in such a Figure. It can be highlighted that the proposed methodology provides a satisfactory estimation of fretting fatigue life, since almost all the results fall within scatter band 2, with an overall T RMS value equal to 1.66 (readers can refer to the work of Vantadori et al. (2021) for the T RMS computation). Furthermore, the crack nucleation orientation computed by means of the present methodology is equal to about 6-11° depending on the test simulated. Note that these values are related to a length of 100  m. Therefore, they should be compared to the first part of the experimental crack paths, where the orientation ranges from 18° to 32° (see Section 3). From such a comparison, it can be highlighted that, although the position and the orientation of the crack towards the centre of the contact are in good agreement with the experimental observations, the present methodology underestimates the real value of the crack angle. The effect of the main parameters involved in the methodology on the results obtained in terms of both fatigue life and crack orientation is hereafter investigated. In particular, such parameters may be divided into three main categories, that is: contact geometry, fretting loading, and material properties.