PSI - Issue 68

D. Tomerlin et al. / Procedia Structural Integrity 68 (2025) 1237–1244 D. Tomerlin et al./ Structural Integrity Procedia 00 (2025) 000–000

1242

6

The experimental results show that Spec. 1.1, heated to 1250 °C in 1 st cycle, has highest fracture toughness J IC = 68.60 kJ/m 2 and K JIC = 120.31 MPa∙m 1/2 , as well as δ IC = 0.046 mm. Specimens 2, 3 and 4, reheated to 590 ° C, 740 ° C and 890 ° C respectively, show the decreasing of fracture toughness. Specimens 5.2 and 5.2C, reheated to 1250 °C in 2 nd cycle (CGHAZ region), partially recovered fracture toughness properties.

Fig. 5. J -Integral resistance curve (Spec. 3.2)

Fig. 6. CTOD resistance curve (Spec. 3.2)

3.2. Fatigue crack growth results The fatigue crack growth testing gives the Paris-Erdogan law constants C and m , as well as the threshold range Δ K th and crack growth rates da/dN with the R 2 coefficient of determination (Table 3). The characteristic da/dN -Δ K fatigue crack growth versus stress intensity factor curves are provided for all the HAZ simulated specimens (Fig. 7).

Table 3. ASTM E647 fatigue crack growth parameters Specimen C m

2

Δ K th [MPa√m]

da/dN [m/cycle]

microstructure

R

1.4 2.4 3.4 4.4 5.4

1.4506E-14 1.8781E-13 6.8541E-13 2.8521E-13 4.9949E-14 7.1852E-14 1.0766E-13 1.1308E-15

4.4865 3.8722 3.6098 3.7946 5.2970 3.9486 4.3649 5.2266

7.68 8.00 8.00 5.08 3.99 7.96 7.70

1.3606E-10 5.897E-10 1.247E-09 1.36E-10 7.619E-11 2.593E-10 7.971E-10 2.434E-10

0.88006 0.89023 0.95801 0.94208 0.90606 0.96564 0.78422 0.93310

-

A (SC CGHAZ) B (IC CGHAZ)

C (FGHAZ) D (CGHAZ)

2.3C 3.3C 4.3C 5.3C

A (SC CGHAZ) B (IC CGHAZ)

10.48

C (FGHAZ) D (CGHAZ)

NOK

The experimental results show that Spec. 3.4, reheated to 740 ° C in 2 nd cycle exhibit the highest crack growth rate da/dN = 1.247E-09 m/cycle. Spec. 5.4, reheated to 1250 ° C in 2 nd cycle exhibit the least crack growth rate da/dN = 7.619E-11 m/cycle, having brittle fractured structure. CGHAZ zone with precipitations on grain boundary has the lowest resistance to fatigue crack growth, as the fatigue limit values are below 5 MPa√m, since the intergranular crack growth occurred.