PSI - Issue 57

Guillaume THOQUENNE et al. / Procedia Structural Integrity 57 (2024) 191–198 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2. High depth crack initiation phenomenon in rolling contact fatigue Generally, the crack initiation in rolling contact fatigue may appears at the maximum shear stress depth, called Hertz depth, noted (HD). To prevent that phenomenon, conventional sizing method consists in considering a case hardening depth (CHD) greater than 2 times the Hertz depth. In the case of induction hardening, which generates a severe metallurgical slope between the hardened surface and the non hardened core, it may happens that the critical zone is moved from the Hertz depth to the transition zone (see Fig. 1), even if the induction hardening depth (IHD) corresponds to the classical rule (IHD > 2.HD).

Fig. 1 Contact shear stresses vs material resistance. a/ Case hardening [1] – b/ Induction hardening.

3. Cetim twin-disc test bench The Cetim twin disc test bench is a Phenix Tribology TE74 machine (see Fig. 2). It consists in applying a constant load on a cylindrical and a crowned specimens in contact (see geometries in Fig. 3), which roll at a constant velocity. It allows to have a slide to roll ratio (SRR) from 0 (pure rolling) to 50% ( = 100 ∙ 2 ∙ 1 − 2 1 + 2 ). This type of contact represents the contact between 2 gear teeth or a rolling element with a ring in bearings.

Upper

specimen

temperature measurement

Upper specimen

Oil injection

Oil

injection

Lower specimen

temperature measurement

Fig. 2. Cetim TE74 twin-disc test bench.