PSI - Issue 68

Martin Nesládek et al. / Procedia Structural Integrity 68 (2025) 527–533

532

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Martin Nesládek et al. / Structural Integrity Procedia 00 (2025) 000–000

Tab. 2. Comparison of stabilized temperatures from FEA due to friction in contact and those from IR measurement. Case of bridge pads.

Θ [°C] from FEA

Θ [°C] from IR measurement

σ a [MPa]

COF = 0.5

COF = 0.8

COF = 1.0

COF = 1.2

COF = 1.4

78.6

0.67 5.49

0.01 1.59 8.41

0.01 0.32 5.05

N/A N/A N/A

N/A N/A N/A N/A

~0.00

125.7 172.8 227.8 263.1

2.66 8.11

16.19 35.31 48.74

22.40 38.00

17.64 28.99

13.62 25.04

15.80 21.49

19.62

4. Discussion To obtain relevant COF values, we performed measurements using digital image correlation (DIC; see Fig. 7a). The evolution of the COF was analyzed over the lifetime of two specimens subjected to different levels of axial stress amplitude. The COF values, determined by using measured and numerically calculated contact slips, are presented graphically in Fig. 7b. It appears that the stabilized COF values relevant for determining contact slips and stresses under the conditions of our experiments fall within the range of approximately 0.55 to 0.60. For example, by using COF = 0.6 and η = 0.8 to simulate the temperatures of specimens due to contact friction, we were able to obtain the self-heating curve for pads with a single contact surface (shown in Fig. 8) after subtracting the simulated temperatures from the measured ones. However, when applying the Matušů method, the error of σ !" relative to conventional fatigue increased (compare Fig. 5a with Fig. 8a). The output from Risitano’s a b

# = 284 # = 175

Fig. 7. (a) Acquisition of images for evaluating contact slips and COF using DIC. (b) Evolution of the COF with the number of cycles.

method (Fig. 8b) closely matches that obtained using as-measured temperatures. It is important to note that with these simulation settings, the computed temperatures for the bridge pads remain significantly higher than the measured values, which prevents effective correction. 5. Conclusion This study shows relatively promising results in terms of the application of the self-heating method to the rapid experimental estimation of fatigue limit under fretting conditions. Good agreement with the conventional measurement approach is achieved already with temperatures without correction for contact friction. The extraction of the effect of contact friction by subtracting the simulated temperatures from the measured ones did not have the desired improving effect and for the case of bridge pads it was not even feasible for the real COF setting. However, the data presented here are very limited to draw a more general conclusion.