PSI - Issue 43

Tereza Juhászová et al. / Procedia Structural Integrity 43 (2023) 172–177 Tereza Juhaszova/ Structural Integrity Procedia 00 (2022) 000 – 000

175

4

Using this direct extrapolation method, one can obtain the values of SIF as well as of the geometry shape function Y I . In order to verify the current 3D model, a comparison with a 2D and 3D model using a rectangular cross-section was done. Additionally, the numerical model generated the values of CMOD, which were used for the assessment of the SIF values from the experimental data. The geometry comparison is presented Fig. 2 (a), while the dependency of K I on the CMOD value is shown in Fig. 2 (b). The values of SIF presented in Fig. 2 (a) indicate rapid increase in the value of SIF for the IPE 80 profile when compared with the values obtained for the rectangular cross-section, especially for the greater ratios of a / W . This is due to the fact that the crack is propagating through the flange plate to the web (the thickness of the flange plate is 5.2 mm). Additionally, the crack grows only in the bottom flange plate, perpendicularly to the crack front, in the direction of the loading of the IPE 80 profile, and once it reached the web, we assume brittle failure of the specimen. 4. Materials and Methods 4.1. ASIS 304 The IPE 80 beams used in fatigue experiments are coldly rolled profiles made of stainless-steel grade of AISI 304. The mechanical parameters and chemical composition of stainless steel AISI 304 for IPE 80 are mentioned in Tab. 1. The resistance to corrosion is obtained by a high content of chrome. On the other hand, the content of nickel is responsible for the microstructure and mechanical properties (Baddoo, 2008; Gardner, 2005). In comparison to structural steel, the mechanical properties of stainless steel show a different trend, especially the stress-strain diagram (Arrayago, 2015). Stainless steel does not have a determined yielding stress, so the proof test is being used.

Table 1. Chemical composition and mechanical properties of AISI 304.

Specimen

C [%]

Si [%]

Mn [%] 1.5 1.6

P [%]

S [%]

Ni [%]

Cr [%] 18 18

N [%]

σ u [MPa] 675 628

σ 0.2 [MPa] 342 255

σ 1,0 [MPa] 380 319

ε tu [%] 55 58

Specimen 1 Specimen 2

0.03 0.4 0.02 0.4

0.03 0 0.03 0

8 8

0.1 0.1

4.2. Experimental Testing Experimental execution of three-point bending was processed using Vibrophore 250, a high-frequency pulsator by ZwickRoell. Dynamic loading is generated by an oscillating system in full resonance. To evaluate the fatigue parameters, crack mouth opening displacement was measured on the bottom flange of the profile, in the middle of the span, where the initial notch was created. This was obtained using a clip-on extensometer, as one can see in Fig. 3, placed on the plates, glued to the bottom flange of the beam. The extensometer measures the CMOD with a high accuracy, but is limited to the measurement of 2 mm maximum. In total, three fatigue experiments were performed, with different stress ratios R of 0.1, 0.3, and 0.5, and different forces applied, i.e., P max = 75; 100; 120 kN.

(a)

(b)

Fig. 3. Experimental configuration (set up) (a), and (b) bottom flange after experiment.