PSI - Issue 75

144 Luca Corsaro et al. / Procedia Structural Integrity 75 (2025) 140–149 Luca Corsaro , Francesca Curà, Raffaella Sesana / Structural Integrity Procedia (2025) 5 experimental evaluation of F pn ∾ results in a stress that produces a bending failure. As a consequence, the value of calculated by means of equation 1 assumes the meaning of ( S F min equals to one). Furthermore, in the specific case of Thermographic Method application, the F pn ∾ value was obtained from the TCM routine (see Section 2.1). 3. Materials and Methods 3.1. Materials The tooth root bending fatigue strength was estimated for two spur gears of different material, geometry and surface treatment. The first gear was induction hardened starting from a C45 steel, while the second gear was case hardened (carburizing surface treatment) from a 20MnCr5 steel. The two tested gears are illustrated in Fig. 2.

Fig. 2. (a) C45 gear; (b) 20MnCr5 gear.

Table 1. Gear parameters.

Geometrical and mechanical data

ISO 6336 coefficients

Gear

Parameter

Value 3 mm

Parameter

Value

m n

Y S Y F

1.82 1.77

z α b x

20

20°

Y ST Y NT Y δ relT Y RrelT Y X σ Flim σ Y S Y ST Y NT Y δ relT Y RrelT Y X σ Flim σ σ Y F

2 1

28 mm

C45 induction hardened gear

-

0.99 1.07

Rz

2.79 µm 720 HV

HV

1

440 MPa 934 MPa

FP-ISO

m n

2.2 mm

1.59 1.75

z α b x

30

17°

2 1

20 mm

20MnCr5 carburized gear

0.25 mm 4.3 µm 970 HV

0.99 1.05

Rz

HV

1

312 MPa 650 MPa 683 MPa

FP-ISO FP-SC