PSI - Issue 19

Okan Yılmaz et al. / Procedia Structural Integrity 19 (2019) 302 – 311 Yılmaz et al. / Structural Integrity Procedia 00 (2019) 000–000

310

9

S500MC (t=6 mm)

S700MC (t=5 mm)

12

12

10.9 (75%) 10.9 (130%) 12.9

(a)

10

10

8

8

10.9 (75%) 10.9 (130%) 12.9

(b)

6

6

1.E+04

1.E+05

1.E+06

1.E+04

1.E+05

1.E+06

Max. applied force (kN)

Max. applied force (kN)

Fatigue life (cycles)

Fatigue life (cycles)

S960MC (t=5 mm)

12

10.9 (75%) 10.9 (130%) 12.9

10

8

(c)

6

1.E+04

1.E+05

1.E+06

Max. applied force (kN)

Fatigue life (cycles)

Fig. 7. Four-point bending fatigue test results for di ff erent levels of pre-tension and applied bending forces: (a) S500MC, 6 mm-thick samples, (a) S700MC, 5 mm-thick samples, (a) S960MC, 5 mm-thick samples. The bands with dashed lines show [ N f / 2 , 2 N f ] scatter band for the pre-tension level of grade 10.9 bolt (130% of the design preload).

6. Conclusions

The conclusions listed below, complemented with the detailed discussions in [11, 12, 13, 22], might lead to various guidelines regarding design rules and best practices for HSS bolted connections subjected to fatigue loading.

• Considering di ff erent hole-making methods, we saw that the chamfered punch was an improvement over the flat punch only when it was aligned to the loading direction as the sharp edge does not face the expected failure location. Significant improvements were achieved via water-jet cutting technique while laser cutting was providing the best fatigue performance. • While the e ff ect of pre-tension under in-plane shear loading was di ff erent for each grade, fatigue results did not indicate an increased fatigue performance with increase bolt pre-tension. S500MC connections with a lower pre-tension performed better at lower stress amplitudes and no significant di ff erences were observed at medium and higher load levels. The detrimental e ff ect of the increased preload was more notable for S960MC samples. • Applying a shot-peened layer covered by a cataphoretic primer coating improved the fatigue life around 20% for four-point bending specimens. As a general remark, we saw that while in-plane shear loading results in cracks appearing within bolted plates, out-of-plane bending cracks originated under the washer head. Fretting marks were observed in both cases. Finite element simulation showed that the failure location does not simply coincide with the region where slip occurs under out-of-plane bending loading contrary to in-plane shear case. The fact that we do not observe a substantial e ff ect of pre-tension for out-of-plane bending loading hints that bending failure mechanism is dominant over fretting failure for this particular loading mode.