PSI - Issue 17

92 Sebastian Vetter et al. / Procedia Structural Integrity 17 (2019) 90–97 Sebastian Vetter/ Structural Integrity Procedia 00 (2019) 000 – 000 . Hypotrochoidal profiles with three and seven tappets were investigated. Due to the different eccentricities , the sides of the profiles appeared convex, concave or flat. The finite element method was used to calculate stress concentration factors for the free profile shapes under torsion loading. All P-SHCs have a diameter ratio 0.5 between the circumscribed circle diameter of the shaft and the outer diameter of the hub (cf. Fig. 1c). a b c 3

H3-convex

H7-concave

H7-flat

Fig. 1. (a) profile generation (b) investigated profile shapes (c) H7-concave P-SHC.

Eccentricity [mm]

Table 1. Parameter of investigated profile shapes of P-SHCs. Profil shape Tappet number Mean diameter [mm] H3-convex 3 37.334

Diameter of inscribed circle [mm] 34.667

Stress concentration factor 1.14

1.333 1.081 0.676

H7-concave 7

37.838 38.648

35.676 37.295

1.26 1.18

H7-flat

7

2.2. Material and surface properties

Two different materials were used for the production of the P-SHCs according to the parameters specified in section 2.1. These two materials were normalized C45E+N (1.1191 according to DIN EN 10027 (1992)) as well as quenched and tempered 42CrMo4+QT (1.7225 according to DIN EN 10027 (1992)). The static and fatigue strength values were determined for both materials (cf. Table 2). For the investigations of the material, specimens were extracted from the semi-finished product at a diameter of 40 mm. This diameter was equal to the circumscribed circle diameter of the shaft. Therefore, a technological size effect due to heat treatment influences could be excluded. The determined ultimate tensile strength and yield strength were averaged from three static tensile tests according to DIN EN ISO 6892-1 (2009). The basic fatigue strength of the material , was investigated with unnotched specimens with a diameter of 7.5 mm. The tests were performed and evaluated according to the modified staircase method by Hück (1983) for 50 % survival probability. The surface roughness was measured in axial direction according to DIN EN ISO 4287 (2009). Due to the different feed speeds during production, the mean surface roughness for shafts and hubs of the materials C45E+N and 42CrMo4+QT differ according to Table 2.

Table 2. Material and surface properties. Material Tensile strength [MPa] C45E+N 687

Tensile yield strength [MPa] 351

Fatigue strength , [MPa] 257

Surface roughness shaft [µm] 5,8

Surface roughness hub [µm] 6,9

42CrMo4+QT

1012

873

439

3,0

3,1

2.3. Experimental setup

In order to develop an approach for dimensioning P-SHCs under static and high cycle stresses, it is necessary for the experimental investigations to focus on load cases which dominate in practice. With regard to the static load capacity of P-SHCs, the static torsional moment as load is essential. A rotating bending load, which can be optionally combined with static torsion as mean stress, is important for the high cycle load capacity. The static torsional moment for the investigation of the static load capacity was applied with the hydraulic rotary cylinder test bench shown in Fig. 2a. The torsional moment was measured by a load cell and the twisting angle between shaft and hub was detected.