PSI - Issue 19

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

309

8

S500MC – Δσ nom =225 MPa

S700MC - Δσ nom =300 MPa

Plasma Drilled Waterjet Laser

Plasma Drilled Waterjet Laser

806%

119%

142%

92%

158%

Punched (Flat) Punched (90°) Punched (0°)

14%

Punched (Flat) Punched (90°) Punched (0°)

31%

0% 2%

16%

(a)

(b)

0%

0%

500%

1000%

0%

500%

1000%

S960MC - Δσ nom =300 MPa

Plasma Drilled Waterjet Laser

567%

249%

161%

Punched (Flat) Punched (90°) Punched (0°)

69%

0% 0%

(c)

0%

500%

1000%

Fig. 6. Fatigue life improvement for samples produced by various hole-making procedures (a) S500MC, 6 mm-thick samples, ∆ σ nom = 225 MPa; (b) S700MC, 5 mm-thick samples, ∆ σ nom = 300 MPa; (c) S960MC, 5 mm-thick samples, ∆ σ nom = 300 MPa. Arrows denote the run-out condition, which corresponds to 5e6 cycles.

fretting fatigue – net section mode. For S960MC samples, the detrimental e ff ect of the increased preload was more notable. On average, all samples with the highest bolt pre-tension endured less fatigue cycles than S960MC samples with the lowest pre-tension. For the detailed analysis, the reader is referred to [13]. The out-of-plane bending loading results obtained for the same pre-tension levels are plotted in Fig. 7. Under this loading mode, we did not observe any consistent e ff ect with respect to the applied bending force or the material as all fatigue life values fall under [ N f / 2 , 2 N f ] scatter band for the mid pre-tension level. Table 2 summarizes the fatigue tests for di ff erent flange configurations. Test side is denoted as the face where tensile stresses occur while pre-tension is applied from the opposite side. We observed lower fatigue lives when the pre-tension is applied over the bolt rather than the nut. Alternative bolt head orientation did not have an e ff ect on fatigue life, however it must be noted that it is di ffi cult to ensure a perfect alignment of both flanges when applying pre-tension from one side. Having a shot-peened layer covered by a cataphoretic primer coating improved the fatigue life is both conditions, 20% in average.

Table 2. Four-point bending fatigue test results for the flanged bolt, alternative bolt head orientation, and shot-peened layer with coating. The material is 5-mm-thick S700MC grade steel and applied maximum bending force is F fpb , max = 10 kN. Fatigue life values (cycles)

M16 grade 10.9 (130%)

Alt. bolt head orientation

Shot-peened

Test side: bolt, torqued over the nut Test side: nut, torqued over the bolt

50621 35156

52128 35825

60055 46096