PSI - Issue 51

Tereza Juhászová et al. / Procedia Structural Integrity 51 (2023) 213–218 Juhaszova et al./ Structural Integrity Procedia 00 (2022) 000–000

214

2

1. Introduction Fracture mechanics is well-known discipline focused on behavior of specimen, parts or materials including cracks, Klesnil & Lukáš (1992), Suresh (1998), Pook (2000). It is necessary to take the difference in behavior of these objects into account accordingly, due to the change of resistance and behavior of materials. Also, location and magnitude of stress field focuses in the vicinity of the crack. To describe the fatigue behavior of material, several tools are being widely used. Most basic and oldest one is S - N curve, describing relation of stress amplitude applied on the cycles to failure. The biggest disadvantage lays in focus only on the fatigue lifetime, neglecting the description of the propagation of the crack itself. On the other hand, more recent tool solving this issue is Paris’ law, Paris (1963), which relates crack growth rate to stress intensity factor range as follows: d d = � (1) where d a /d N stands for the crack fatigue growth rate (FCGR), as the change in crack length depending on number of cycles performed, and K I stands for the stress intensity factor range, depending on the stress ratio during loading. C and m are material constants depending on loading condition, environment, stress ratio, etc. The most common variable used in fracture mechanics is stress intensity factor, whose dependence on applied stress σ could be calculated according to Irwin (1957) as follows: � = √ � ( , (2) where describes relative crack length and � ( is a shape function depending on geometry of the specimen and loading type, as well as on the relative crack length. This paper describes describe evaluation of fatigue testing of IPE beams of two most common stainless-steel grades (AISI 304 & AISI 316) used in civil engineering, see Gedge (2008), Baddoo (2008), Gardner (2019). Comparison of results was performed using Paris-Erdogan law. Different stress ratios ( R = 0.1, 0.3, and 0.5) are used as variables for the test, which are expected to provide reference data for subsequent fatigue crack propagation analysis.

1.1. Material properties

The experimental study took place on coldly rolled IPE cross section specimens. Product label IPE 80 × 46 × 3.8 × 5.2 mm, describes the important dimensions of the profile, followed by 6000-6200 mm, which described the length of the bar from which the components were manufactured. Following tables includes chemical composition of materials guaranteed by producer, as well as mechanical properties verified experimentally, for each grade individually.

Table 1 Chemical composition and mechanical properties of selected grades

Specimen grade AISI 304

N [%] 0.05

C [%]

Si [%] 0.44

Mn [%] 1.56

P [%] 0.03

S [%]

Ni [%]

Cr [%] 18.2

N [%]

0.017

0.002

8

0.05

AISI 316

0.012

0.024

0.48

1.18

0.03

0.002

10.55

16.9

0.012

Table 2 Experimentally verified mechanical properties

σ 1.0 [MPa]

ε [%]

HB

Specimen grade AISI 304

σ u [MPa]

σ 0.2 [MPa]

628

255

319

58

162

AISI 316

599

343

378

48

169