PSI - Issue 24

Bruno Atzori et al. / Procedia Structural Integrity 24 (2019) 66–79 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

77

12

10.00

HT60 - 90° HT60 - 120° HT60 - 135° HT60 - 150° SS41 - 90°

0.01 0.10 Averaged strain energy density [MJ/m 3 ] SS41 - 120° SS41 - 135° SS41 - 150° ΔW A,50% = 0.44 MJ/m 3 N A = 2 ∙10 6 cycles Scatter Index (10%-90%): T W = 0.57/0.33 = 1.73 T σ = √T W = 1.31 Slope k = 2.35 ΔW A,50% = 0.13 MJ/m 3 N A = 2 ∙10 6 cycles Scatter Index (10%-90%): T W = 0.18/0.10 = 1.80 T σ = √T W = 1.34 Slope k = 2.27 Strain energy density Intensity Factor [kJ/m 2 ] HT60 - 90° HT60 - 120° HT60 - 135° HT60 - 150° SS41 - 90° SS41 - 120° SS41 - 135° SS41 - 150° 1.00 1.E+03 1.E+04 0.01 0.10 1.00

0.44 0.57 0.33 0.18 0.10 0.13

SED-based design scatter-band for HT60 steel (R 0 = 0.064 mm) load ratio R = 0.05 SED-based design scatter-band for SS41 steel (R 0 = 0.208 mm) load ratio R = 0.05

(a)

N A

1.E+05

1.E+06

1.E+07

Number of cycles to crack initiation, Ni

L A,50% = 0.0274 kJ/m 2 N A = 2 ∙10 6 cycles Scatter Index (10%-90%): T L = 0.0354/0.0211 = 1.68 T σ = √T W = 1.30 Slope k = 2.30

SEDIF-based design scatter-band for HT60 and SS41 steel, load ratio R = 0.05

0.0274 0.0354 0.0211

(b)

N A

0.00

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

Number of cycles to crack initiation, Ni

Figure 4: Fatigue test results (Kihara and Yoshii 1991) expressed in terms of (a) averaged SED and (b) SEDIF parameters over cycles to crack initiation Ni (ai = 0.2 mm) for different V- notched flat bar specimens (2α = 90°, 120°, 135° and 150°) of mild steel (SS41) and of high-strength steel (HT60) subjected to tensile loading. Nominal stress ratio R=0.05 (see also (Lazzarin and Zambardi 2001)).