PSI - Issue 75

Tomáš Karas et al. / Procedia Structural Integrity 75 (2025) 150–157 T. Karas et al. / Structural Integrity Procedia 00 (2025) 000–000

152

3

2. Material and Methods

2.1. Material

The material 42CrMo4 + QT used for the sample manufacturing was consistent (the same heat No. T46157) with the steel used in the experimental campaign of Papuga et al. (2023). The steel underwent a quenching and tempering heat treatment process prior to manufacturing the fatigue samples to achieve the desired mechanical properties (Table 1.).

Table 1. Material properties of 42CrMo4 + QT steel (Heat No. T46157) Tensile strength

Tensile yield strength

Elongation at fracture

1097MPa

1002MPa

16.5%

2.2. Test sample and fretting pads

The samples (Fig. 1. (a)) were machined from the centres of round 35 mm diameter bars. First, a round cross-section with a diameter of 11.3 mm was created in the narrowed central part, followed by milling from four sides to obtain a 7.5 x 7.5 mm square cross-section. In this study, two di ff erent fretting pad geometries were employed (Fig.1. (b, c)), both with a contact face width of 7.5 mm, that is, the same as the width of the sample. The first geometry was a single contact pad with a flat surface contact and rounded edges with a radius r = 50 mm. The second geometry was a double contact pad, also known as bridge type, with a radius r = 1 mm at the edges. Both pads were made from the same 42CrMo4 + QT steel as the test samples. Furthermore, all surfaces for self-heating measurement were coated with black LabIR paint with high emissivity ( ε T = 0.963) as shown in Fig. 1. (d).

2.3. Conventional Fretting Fatigue Tests

For all Fretting fatigue tests, an Amsler 10 HFP 422 electromagnetic pulsator was used, with measuring set-up shown in Fig. 2. (a). The sample is first loaded with a mean axial force corresponding to the test R-ratio, and after that, the fretting pads can be placed in contact. The fretting pads are then aligned with the width of the sample and loaded with normal force through tightening the screws in a free proving ring. The ring is equipped with strain gauges calibrated to measure the normal force. For both pad geometries, the normal force applied is comparable (9.0 kN for

(b)

(a)

Fig. 2. (a) Combined fretting fatigue and self-heating set-up; (b) Acquisition software with the thermal camera view.