PSI - Issue 19

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

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Fig. 2. Sample geometries for the experimental setups (units in mm): (a) axial fatigue test with holed specimen, (b) single shear lap bolted joint test, (c) four point bending test. (d) edge distances used in plates and bolt / nut main dimensions. Extensions represent the dog-bone shape that is utilized to ensure a constant stress flow within the central section of the sample. For (a), full specimen dimensions are provided in [11, 12] and for (b), in [13].

ratio is R = 0 . 1 and frequency is 25 Hz. These fatigue loading amplitudes are chosen after an initial experimental study with the intention of obtaining fractured samples between 2e5 and 2e6 cycles.

2.3. Four-point bending test

To reproduce the out-of-plane bending loading mode illustrated in Fig. 1, we use a four-point bending test set-up, see Fig. 2c. The bolted specimen consists of a single rectangular-shaped plate bolted with a M16 flanged bolt and its respective flanged nut. Tests are carried out at 20 Hz with a load ratio of R = 0 . 1 and at three applied maximum force levels: F fpb , max = 8, 9, and 10 kN. These force levels are defined to obtain fracture under 2e6 cycles.

3. E ff ects influencing the fatigue performance

3.1. Hole-making procedure

Hole-making procedures are essential to allocate the fastener elements in bolted connections, however they may induce defects and residual stresses that in turn a ff ect the fatigue behaviour, especially in cases without any pre-tension. To study this e ff ect on HSS grades, axial fatigue tests are performed using HSS plates with holes manufactured using several mechanical (punching, drilling, and water-jet cutting) and thermal (laser cutting and plasma cutting) hole making techniques. For a detailed account of the cutting parameters of all techniques employed here, see [11, 12]. Two di ff erent punch geometries are considered for the punching process: flat and chamfered. To evaluate the influence of the sharp edge in the chamfered punch, we consider two orientations: (i) aligned (0 ◦ ) and perpendicular (90 ◦ ) to the loading direction.