PSI - Issue 17

Felix Kresinsky et al. / Procedia Structural Integrity 17 (2019) 162–169 Felix Kresinsky / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 1. Material data of examined specimens and failure criterion to be investigated.

R e , R p0,2 yield strength

R m tensile strength

Material (hub)

potential failure criterion

Material (shaft)

C45/1.1191 (normalized)

C45/1.1191 (normalized) C45/1.1191 (normalized)

360 MPa

635 MPa

keyway expansion + shaft crack

42CrMo4+QT/1.7225 (quench and tempered) 16MnCr5E/1.7131 (case hardened)

840 MPa

989 MPa

keyway expansion + shaft crack

16MnCr5E/1.7131 (case hardened)

659 MPa

918 MPa

keyway expansion + shaft crack

The basic geometry and material parameters of the main variant are shown in Table 2. The length of the hub always equaled the load-bearing length of the key. The seat of the hub was joined according to the sketch in Table 2. No relative interference fit was between shaft and hub.

Table 2. Basic geometry and material data of the main variant with the assembling position of the hub.

Parameter

Main variant

unit mm mm mm mm mm

shaft diameter d

40 51 80

load-bearing length of key l tr

Small shouldered hub outer diameter D 1 Big shouldered hub outer diameter D 2

165

Width of big shouldered hub c

21

Length ratio l tr /d

1,3 0,5 0,5 0,0

- - - - - -

Diameters ratio d/D 1

Limit case of load diversion a 0 /l tr

‰

Relative interference

Material hub Material shaft Material key

C45+N/1.1191 (normalized) C45+N/1.1191 (normalized) C45+QT/1.1191 (quenched and tempered)

Frequency f load ratio R

20

Hz

0

-

2.3. Determination of the keyway expansion

As already discussed at the beginning, torsional loaded keyed shaft-hub connections must be designed according to two different criteria: this work is mainly focused on the permissible surface pressure. The actual surface pressure in the contacts between the keyways flanks and the key is not explicitly measurable, especially not during a dynamic test. For this reason, the plastic deformation of the shaft keyway is used as a measurable result of the surface pressure. As shown in Fig. 2 each keyway was measured at three locations (z/l tr = 0 | 0.5 | 1 [cf. Tab. 2]). The keyway was measured three times (Fig. 2): The first measurement documents the initial condition of the shaft keyway. The second measurement shows the plastic deformation of the keyway due to the joining of the key. The third measurement shows the deformation/expansion of the keyway after the experiment. It was shown that the width of the shaft keyway is already outside its manufactured tolerance field of 12P9 (-61µm to -18 µm) due to the joining of the key (2nd measurement - 1st measurement, Fig. 2). The yield strength of the key is 2.5 times higher than that of the shaft material. Therefore only 10-20 µm interference between shaft keyway and key remains after the key is inserted. In order to be able to assess only the result of the torsional stress acting on the shaft keyway, the keyway expansion discussed subsequently (see chapter 3) always describes the difference between the 2nd and 3rd measurement.