PSI - Issue 28

Barış Tanrıkulu et al. / Procedia Structural Integrity 28 (2020) 1267 – 1275 Author ame / Structural Int grity Procedia 00 (2019) 00 – 00

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Fig. 3. Representation of the Junker test machine

3. Results and Discussion

As a result of the performed Junker vibration tests, clamp load-cycle graphs of each combination were drawn and a comparison was made between loosening rates. Accordingly, for 29 mm clamp length, it was found that the loosening rate of the flat nut was the highest among the other two combination. The effect of tightening strategies was revealed in DIN 6923 nuts with a rip form under the flange. Accordingly, it was found that fastening from bolt head provides better vibration resistance compared to fastening from nut side. The reason for this behavior was explained by the rip form of the nut as deforming the plate. The results and comparisons of the tests performed for combinations with 29 mm locking length and 175 HV plate hardness are given in Figure 4-a. One of the most important factors affecting the loosening resistance of fasteners is the clamp length. For this reason, tests were repeated with bolts having 40 mm clamp length and plates with 175 HV hardness. In this way, the loosening resistance between tightening strategies could be revealed based on the clamp length. Accordingly, the experimental studies showed that the order of the loosening rate of different tightening strategies was the same. However, the effect of the tightening strategies was more obvious, i.e. the difference in loosening rates were higher (Figure 4-b). In the third set of the experimental study, tests were carried out by using plates with 300 HV hardness and bolts with 40 mm clamp length. Results on 300 HV hardness values showed that loosening resistance decreases with the increase of the hardness value (Figure 5-a). Accordingly, with the comparison of the test results performed with plates having 300 HV and 175 HV hardness for 40 mm clamp length, it was determined that the loosening resistance decreased with the increase of plate hardness (Figure 5-b). This situation was determined to be due to the reduction of the deformation created by the rip form on the plate surface. Tightening method had a direct effect on the amount of deformation on the plate. Images containing the deformation shapes on the plate surface as a result of the tests are given in Figure 6. It was revealed that when the connection is tightened from the bolt head, the rip form under the flange deformed the plates and contributed to increase in vibration resistance, since the nut was directly exposed to axial load.