PSI - Issue 19

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

304

3

loading. Numerical work is summarized in Section 4. Sections 5 and 6 provide a synthesis of the obtained results and conclusions.

2. Materials and methods

The steel grades considered in this study, namely S500MC, S700MC, and S960MC are thermomechanically rolled (M) structural steels (S) suitable for cold forming (C) while the numbers denote the minimum yield strength in MPa at ambient temperature [4]. The mechanical properties of the steels are provided by a related work package within the same European Research project [5] where the employed procedure is partly described in [6]. The chemical compositions of the steels are provided by the manufacturers [7, 8, 9] and summarized in Table 1 together with the mechanical properties. It must be noted that S500MC plates are of 6-mm thickness while S700MC and S960MC plates have the thickness of 5 mm.

Table 1. Chemical composition and mechanical properties of the HSS grades S500MC, S700MC, and S960MC. Chem. comp. (wt%)

C

Si

Mn

P

S

Al

Nb

V

Ti

Mo B

S500MC S700MC S960MC

≤ 0 . 120 ≤ 0 . 500 ≤ 1 . 700 ≤ 0 . 025 ≤ 0 . 015 0 . 015

≤ 0 . 090 ≤ 0 . 200 ≤ 0 . 150 -

-

≤ 0 . 120 ≤ 0 . 600 ≤ 2 . 100 ≤ 0 . 025 ≤ 0 . 015 ≥ 0 . 015 ≤ 0 . 090 ≤ 0 . 200 ≤ 0 . 220 ≤ 0 . 5 ≤ 0 . 0050 ≤ 0 . 120 ≤ 0 . 250 ≤ 1 . 300 ≤ 0 . 020 ≤ 0 . 010 ≥ 0 . 015 ≤ 0 . 050 ≤ 0 . 050 ≤ 0 . 070 - -

Mechanical properties

ε f (%)

HV0 . 2

E (GPa)

σ y (MPa)

σ UTS (MPa)

S500MC S700MC S960MC

210 210 210

562 ± 6 731 ± 3 977 ± 7

658 ± 4 801 ± 4 1061 ± 8

13 . 7 ± 1 . 2 11 . 8 ± 0 . 6 3 . 2 ± 0 . 2

207 ± 7 266 ± 9 344 ± 6

Experiments are detailed in below subsections while sample geometry and loading information are provided in Fig. 2. To study the manufacturing e ff ects on hole-making, we utilize axial fatigue tests of holed samples. Shear lap bolted joints are used to assess the in-plane shear loading mode and four-point bending fatigue tests reproduce the out-of-plane bending loading mode. The edge distances have been chosen in accordance with the Eurocode standard (EN 1993-1-8) for bolted joints [10] while every bolt that we use in this study is an M16 bolt. Three repetitions are performed for each defined test condition.

2.1. Axial fatigue test

The uniaxial fatigue tests are designed to study the e ff ect of the hole-making procedures on the base material. No bolt or washers are included to isolate the e ff ect of the hole-making process. Figure 2 gives the edge distance and hole dimension of the dog-bone specimen and detailed specimen dimensions can be found in [11, 12]. Similar sample designs were employed in [14, 15] in studies on punched and thermally-cut holes, respectively. The fatigue tests are performed at 25 Hz and with a load ratio of R = 0 . 1. Two nominal stress amplitudes are used: ∆ σ nom = 225 MPa for the 6-mm-thick S500MC samples and ∆ σ nom = 300 MPa for the 5-mm-thick S700MC and S960MC.

2.2. Shear lap bolted joint test

A shear lap joint is employed to reproduce the in-plane shear loading mode and presented in Fig. 2b. The test sample is formed by two identical half dog-bone shape steel plates joint by a M16 flanged bolt and its respective flanged nut, see Fig. 2d for the edge distances and bolt / nut dimensions, and please refer to [13] for the full specimen geometry. Tests are carried out at three nominal stress amplitudes: ∆ σ nom = 120, 145, and 170 MPa while the load