PSI - Issue 42

Lukáš Suchý et al. / Procedia Structural Integrity 42 (2022) 1128–1136 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1130

3

2.1. Test bench The test bench used for the present investigations is able to apply rotating 4-point-bending and dynamic torque to the specimen. It has already been described in [16]. Although different amplitude ratios, frequency ratios, mean torsional stresses and phase shifts can be set, the variation of these stress-multiaxiality parameters was not a focus of the present study. With the aim of investigating the material effect, the tests were performed at the single stress amplitude = and frequency = = 15 Hz . The tests were carried out using the staircase method according to Hück [17]. The limit for load cycles was 10 7 . 2.2. Specimen and material The test geometry is summarized in Table 1 . The shaft shoulder was designed so as to take the known notch sensitivity of the stronger steels into consideration. This results in a lower shoulder height for the 42CrMo4 steel, which means that the notch factor = / (according to DIN 743 [13]) is almost the same for both materials. The initial diameter of the semi-finished product during production was 75 mm; the critical cross section was 40 mm. This corresponds to a typical reference shrink-fit type with a sharp contact edge from DIN 743, for which numerous results are available. The joining process of the press-fit connection was carried out by heating the hub to 280°C and cooling the shaft down to – 30°C. According to DIN 7190[18], a relative interference of = / = 1.7 per mil was selected, which leads to a nominal contact pressure of = 134 MPa . The concentricity as well as the reliable interference of the connection is ensured by measuring and matching the geometrical outlines of the shaft and hub. Table 1. Specimen geometries and materials

Filleted shaft

Interference fit connection

40 mm

40 mm

Shaft diameter Hub thickness Q A

Shaft diameter

D F

d

0.5

4 mm; 2 mm

Fillet depth

D F / D A

t

1.7 ‰

0.4 mm

Relative interference ξ w Relative joining length l rel

Radius

I / D F l F / D F

r

0.9

48 mm; 44 mm

Fillet diameter

D

C45+N, 42CrMo4+QT (hub + shaft)

C45+N; 42CrMo4+QT

Material

Material

Table 2 summarizes the material properties. The results from the tensile tests represent the material properties at the failure diameter of = = 40 mm. The corresponding fatigue parameters were determined using DIN743 with a conversion factor of = 0.4 . Using Eq.(1) and (2) , the fatigue strength was determined for repeating tension and torsion according to [19] and [20], respectively, The torsional fatigue strength is calculated from −1 = −1 /√3 . 0 = 2 ∙ −1 /(1 + 0.35 ∙ 10 −3 ∙ /MPa − 0.1) (1) 0 = 4 ∙ −1 2 ∙ −1 0 + 1 (2)