PSI - Issue 60

B Shashank Dutt et al. / Procedia Structural Integrity 60 (2024) 690–699 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

694

5

100 150 200 250 300 350 400 450

300 o C 350 o C 400 o C 450 o C 500 o C 550 o C

a

b

1000

300 O C 350 O C 400 O C 450 O C 500 O C 550 O C

300

800

350

550

500 Tearing resistance, dJ/da 400

550

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400 J, kJ.m -2 600

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0 50

450

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 a, mm

 a, mm

Fig.3. (a) J-R curves; (b) Tearing resistance at various temperatures.

J -R curves at different temperatures are plotted in Figure 3 (a). Tearing resistance (dJ/da) values at different temperatures are plotted in Figure 3b. From J -R curves, J 1c values were determined. The blunting line for determination of J 1c is estimated using equation 3. J 1c values are included in table 3. J 1c values for all temperatures satisfy ASTM 1820 plane strain criterion (ASTM 2017) to be qualified as material property. Minimum thickness of specimens (B) required to qualify plane strain criterion was estimated as per equation 4. From Fig.3b, it is observed that slopes of Tearing resistance curves with test temperatures are similar to slopes of J -R curves (Fig.3a). At 300 and 350 °C, slopes of both J -R curves and Tearing resistance curves are similar. From Table 3, it is observed that change in fracture toughness ( J 1c ) values (239 and 246 kJ.m -2 respectively) at 300 and 350 °C was marginal. Decrease in slopes of both J -R curves (Fig.3a) and Tearing resistance curves (Fig.3b) was observed at 400, 450 and 500 °C, compared to the corresponding slopes at 300 and 350 °C. Decrease in J 1c values (195-200 kJ.m -2 ) was observed at 400-450 °C, compared to the fracture toughness at 300 and 350 °C (Table 3). Dutt et al. (2018) reported similar trends of minima in J 1c values, in the temperature range of 350 450 °C. Decrease in fracture toughness (350-450 °C) was (Dutt et al. 2018) explained based on the presence of dynamic strain aging (DSA) in P91 steels. In this study, increase in J 1c values was observed in the range 500-550 °C (Table 3). From Fig.3a and Fig.3b, it is observed that slopes of both J -R curves and Tearing resistance curves are higher at 550 °C, compared to other test temperatures. Dutt et al. (2018) observed increase in fracture resistance at 500-550 °C, compared to J 1c values at 350-450 °C. Increase in fracture resistance in the temperature range 500-550 °C, was (Dutt et al. 2018) explained based on absence of DSA. In this study, J 1c value, slope of J -R curve and slope of tearing resistance curve (Table 3, Fig.3a, Fig.3b) was higher at 550 °C, compared to other test temperatures. Based on observations by Dutt et al. (2018), in this study, it can be inferred that higher fracture resistance (Tearing resistance and J 1c value) at 550 °C, compared to other test temperatures was due to absence of DSA. 4 ( ) a J f    (3)

YS  = Yield strength (YS),

f  = flow stress =(YS+UTS)/2 , UTS= ultimate tensile strength, Δa= crack

where

extension

J C

10(

)

B

1 flowstress



(4)