PSI - Issue 22

Z. Marciniak et al. / Procedia Structural Integrity 22 (2019) 393–400 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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life calculations it is necessary to reduce the multiaxial stress state to the uniaxial one (usually corresponding to normal stress), so the fatigue failure criteria must be applied. They can be divided into stress, strain and energy based criteria. The most often applied and verified criteria are the following: (i) the stress criteria proposed by Gough and Pollard (1935), Nishihara-Kawamoto (1945), Findley (1959), McDiarmid (1987), Zenner et al. (2000), Macha (1989), Dang Van (1989), Sonsino (1987), Papadopoulos (1994), Carpinteri et al. (2014), Rozumek and Marciniak (2011), (ii) the strain criteria formulated by Brown and Miller (1973), Lohr and Ellison (1980), Socie et al. (1993), Bantachfine et al. (1996), (iii) the energy criteria proposed by Liu (1993), Varvani-Farahani (2000), Ellyin et al. (1991), Chen et al. (1999), Łagoda and Macha (2001, 2002) Rozumek et al. (2010, 2012), Lachowicz (2001), Gasiak and Pawliczek (2003), Correia et al. (2017) and other (Brighenti et al., 2012). Only some of these criteria were considered under non-proportional loadings. Their usability in fatigue life calculations is evaluated together with the chosen hypothesis of damage accumulation, and the calculated fatigue life N cal is compared with the experimental one N exp . The aim of this paper is to compare the calculated fatigue lives with experimental ones obtained from tests under proportional and non-proportional bending and torsion with different amplitude ratios in specimens made of 10HNAP steel.

Nomenclature E

Young’s modulus

N R

number of cycles crack growth

load ratio

Poisson’s ratio



ultimate tensile stress

 u  y

yield stress

k

fatigue limits ratio calculated life experimental life

N cal N exp

N f

number of cycles to failure

R  

stress ratio

means atan (M Ba /M Ta ) of the bending to the torsional moments coefficient of sensitivity for loading phase shift phase shift  af ,  af fatigue limit under plane bending and torsional, respectively 

2. Experimental procedure Round specimens made of a low-alloy 10HNAP (S355J2G1W) structural steel were tested. Metallographic tests of the material show a fine grained ferritic-pearlitic structure. Table 1 contains mechanical properties of the tested steel.

Table 1. Mechanical properties of the material.

Material

 y (MPa)

 u (MPa)

E (GPa)



 af (MPa)

 af (MPa)

N f (cycles)

S355J2G1W

418

566

215

0.29

300

162

3  10 6

Figure 1 shows a shape and dimensions of specimens. They were cut from the sheets 16 mm in thickness according to the rolling direction. The specimen surfaces were ground and polished. The tests were carried out at the test stand