PSI - Issue 38

Kimiya Hemmesi et al. / Procedia Structural Integrity 38 (2022) 401–410 Author name / Structural Integrity Procedia 00 (2021) 000 – 000

403

3

Material tensile properties, including both monotonic and cyclic stress-strain curves, were determined using smooth cylindrical specimens. Fatigue tests were performed on cylindrical samples containing V-shaped circumferential polished notches, with the notch angle of 120° and the notch root radius of 1 mm. The net cross-section diameter was 4 mm for the steel specimens and 8 mm for the aluminium specimens, see Fig. 1. The selected specimen geometries assure material yielding in the notch root at overloads, with limited depth penetration of plastic strains and their moderate magnitudes (c.f. Fig. 5). 2.2. Monotonic and cyclic stress-strain curves The engineering stress-strain curves for the two materials determined under quasi-static loading conditions are shown in Fig. 2, the respective tensile properties are summarised in Table 1. The properties are specified both as engineering and true values. The cyclic stress vs. strain curves were determined by means of incremental step tests and curve fitted according to Ramberg and Osgood (1943) ε a = σ a E + ( σ a K ′ ) 1/n ′ . (1) Here, σ a and ε a are the stress and strain amplitude, respectively, K ′ is the cyclic strain hardening coefficient, and n ′ is the strain hardening exponent. The material parameters used in Eq. (1) are summarised in the Table 2. a) b)

Fig. 2. Stress-strain curves from tensile test: a) 42CrMoS4, b) EN AW-6082.

Table 1. Material tensile properties.

Gauge length in mm

Young’s modulus

Yield strength in MPa

Tensile strength in MPa

Fracture stress in MPa

Uniform elongation

Elongation at fracture

Reduction of area

Type of stress-strain calculation engineering

Material

in GPa

--

--

--

42CrMoS4

1156 1164

1227 1292

869

0.053 0.052 0.062 0.060

0.162

0.529 0.752 0.354 0.438

20

220.9

true

1844

--

EN AW-6082

engineering

359 361

387 411

295 457

0.131

20

70.5

true

--

’ ’ in GPa in MPa --

Table 2. Parameters of the cyclic stress-strain curves.

Material

42CrMoS4

220.9

1444

0.064 0.072

EN AW-6082

70.5

555