PSI - Issue 75

Luca Corsaro et al. / Procedia Structural Integrity 75 (2025) 140–149 Luca Corsaro , Francesca Curà, Raffaella Sesana / Structural Integrity Procedia (2025)

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Table 1 summarizes the main parameters of both tested gears. More in detail, geometrical (m n , z, α, b and x) and mechanical (Rz and HV) parameters are illustrated on the left column. On the right column, the ISO 6336 Standard coefficients (Y S , Y F , Y ST , Y NT , Y δrelT , Y RrelT , Y X and σ Flim ) (ISO 6336-3 (2019) and ISO 6336-5 (2019)) are presented for the evaluation of tooth root stress ( σ F ), and an estimation of the permissible bending stress ( σ FP-ISO ) is also reported. In particular, the two materials under consideration were classified in the Eh (20MnCr5, carburizing surface treatment) and IF (C45, induction hardening surface treatment) typologies. Moreover, a reference value of the fatigue limit (F pn ∾ ሻ obtained from a classical Staircase analysis was evaluated for the 20MnCr5 gear, obtaining 14.60 kN with a standard deviation of 1.06 kN respectively. This way, the permissible bending stress evaluated from an experimental campaign ( σ FP-SC ) was also proposed, and the value was properly corrected in order to take into account the 1% failure probability results and considering the correction coefficient for STBF testing condition (Stahl (1999)). In order to measure the thermal emissions during the fatigue tests, the gear was carefully painted with black paint, which allows to set a known emissivity value of 0.95 according to the value suggested in the reference tables (f. i. FLIR). 3.2. Thermal signal processing The bending fatigue tests were carried out by using the Single Tooth Bending Fatigue (STBF) configuration, and a dedicated equipment was designed and realized to perform bending fatigue tests at high testing frequency with a mechanical pulsator.

Fig. 3. (a) Experimental setups; (b) Thermograms. Fig. 3 shows the experimental setups (Fig. 3 (a)) and the thermograms obtained during the bending fatigue tests (Fig. 3 (b)) for both the tested gears. A thermal camera (Fig. 3(a) n°1) with a minimum temperature resolution of 0.1 K and a spectral range of 7.5- 13 μm was utilized to acquire the surface thermal maps. It was located 65 mm distant from the tested gear and a sampling frequency of 0.1 Hz was adopted during the acquisition. Moreover, a reference sample ((Fig. 3(a) n°3) was located near the gear with the aim of acquiring the environment temperature during the fatigue test. The thermal signal processing of the gear, which was crucial for the thermal parameters computation, was performed for the tensile zone of the upper tooth (see Fig.3(b) n°4 in the upper tooth) by using a measurement point of 2x2 pixel located at the tooth root near the 30° tangent lines (ISO 6336-3 (2019)). The temperature evolution produced from the reference sample (see Fig. 2 n°3) was also processed in order to consider the relative temperature