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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Fig. 2. Schematic procedure for determining the keyway expansion: 2 nd -1 st Measurement is the keyway expansion due to the jointing of the key (without torsion); 3 rd - 2 nd Measurement is the keyway expansion due applied torque load

3. Experimental Results

3.1. Determination of the permissible load on the basis of the permissible surface pressure

This paper focuses on keyed shaft-hub connections under torque load and its damage effects between the key and shafts keyway. The first step was to investigate the durability of a keyed shaft-hub connection on the basis of the permissible surface pressure. The measurement of the plastic shaft keyway expansion (3 rd measurement - 2 nd measurement) is exemplary shown for two different bearing-lengths (l tr /d = 0.95 and 1.3) in Figure 3 a. The three measuring points along the load-bearing length at 3 different load levels are shown. A new specimen was used for each load level. It is clearly visible that the load introduction side (Fig. 3a left) is always subjected to maximum stress and consequently the expansion decreases with increasing keyway length. The expansion increases with increasing torque level, as expected. The failure criterion was defined as a maximum keyway expansion of 50 µmwith a reference diameter d = 40 mm. This determination results in the experimentally obtained permissible torsional moments which are shown in Fig. 3 b for the different bearing lengths l tr /d = 0.95 and 1.3 as well as for short connections (l tr /d = 0.5). For the (long) connection with l tr /d = 1.3 the permissible 50 µm keyway expansion lead to a permissible torsional moment of M t = 1400 Nm. The standard value matches the experimental results for the long connections. With decreasing bearing length, the differences between DIN 6892 and experiment increase. A torsional moment up to 50% higher can be transmitted than currently reported in DIN 6892 with the (short) keyed connection l tr /d = 0.5. Furthermore, it becomes clear that the transmissible torsional moment does not increase any more from a length of l tr /d ≈ 0.95. Therefore an optimum has been achieved because of the inhomogeneous distribution of the surface pressure along the length of the key does not permit any further increase in the transmittable torsional moment.

Fig. 3. a) Experimentally determined plastic keyway expansions at different loads and load-bearing lengths; b) Comparison of the experimentally determined permissible torsion moments with the dimensioning according to DIN 6892