PSI - Issue 14

Ashish Vaidya et al. / Procedia Structural Integrity 14 (2019) 410–415 Ashish Vaidya et al. / Structu al Integrity Procedia 00 (2018) 00 – 00

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Fig. 1. Sample drawing for notched creep specimen (All dimensions are in mm).

Fig. 2. Machined V-notched creep specimen.

3. Result and Discussion

3.1 Stress Rupture Test

Stress rupture tests were carried out on V-notched specimens with notch depth of 0.5, 1.0, and 2.0 mm. The net applied stress level was 195 MPa and the test temperature was 650 °C. The stress level, rupture life and minimum creep rate for various notch depths is given in Table 3.

Table 3. Stress rupture test data. Notch Depth (d) mm Rupture Life (h) Minimum Creep Rate (h -1 ) 0.5 865 3.03E−05 1.0 1770 7.15E−06 2.0 3308 9.68E−07

From the above table, it can be seen that the creep rupture life increased with the increase in notch depth at the same net applied stress level of 195 MPa. It implied that the grade 92 steel shows notch strengthening effect. The notch strengthening effect of grade 92 steel was also observed by Ni et al. (2014), Ni et al. (2015) for U-shaped Bridgman notched specimens. The creep rate decreased by the order of one for increased in notch depth as shown in Table 3. The creep rupture life data is plotted on histogram as shown in Fig. 3 (a). The relationship between notch acuity ratio with creep rupture life is shown in Fig. 3 (b). The creep life of Kt 2 specimen increased by 2 times as compared to the creep life of Kt 1 specimen whereas the creep life of Kt 3 specimen was increased by almost 4 times as compared to the creep life of Kt 1 specimen. This multifold increase in creep rupture life is attributed to the significant accumulation of tri-axial stresses at the notch root of Kt 2 and Kt 3 specimens. The typical creep curves and