PSI - Issue 60

P.K. Sharma et al. / Procedia Structural Integrity 60 (2024) 335–344 P.K. Sharma/ StructuralIntegrity Procedia 00 (2023) 000 – 000

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control loadings. The rate of displacement used during loading is 0.2 mm/min. In the process of unloading, the rate has been kept at a lower value of 0.05 mm/min.

Table 2: Test matrix used for determination of fracture toughness of Alloy 690 material. Test No. Temperature (˚C) Specimen type Material 1 25 Single edged notched tension (SENT) Alloy 690 2 700 3 800 4 1000

The initial crack length (a 0 ) of the fracture specimens is taken as 12.5 mm and width of the specimen (W) is 25 mm. The initial value of a/W for all the specimen is 0.5. A large number of fatigue loading cycles were applied for fatigue pre-cracking of the specimen and procedure outlined in ASTM E1820 has been followed in this work. Peak load during fatigue cycles was maintained well below the limit load of the specimen. A sharp crack tip in the fracture specimen was obtained after fatigue pre-cracking. The pre-crack length for all the specimens is around 0.5-0.7 mm that was obtained by fixing the number of fatigue cycles. The a 0 /W of the fracture specimen used for the test falls in the range of 0.5-0.52. A testing algorithm of the machine was used for conducting the loading and unloading of the specimen according to the user-defined intervals with a given loading and unloading displacement rates. The temperature was set on the controller and the equilibrium was achieved before starting the testing algorithm. After the fracture test is completed, the specimen is heat-tinted to mark the zone of ductile crack growth during the test. Subsequently, the specimen was broken into two parts using fatigue post-cracking in order to examine the fracture surface. The SENT specimen before and after the fracture tests are shown in Fig. 2(a) and Fig. 2(b). Three distinct crack growth can be seen on the fracture surface from Fig. 2(c), i.e., fatigue pre-crack, crack growth zone and post crack zone. The extent of the crack growth was measured using nine point measurement technique.

Fig. 2: (a) Picture of SENT specimen before fracture test; (b) Crack growth as seen from the surface of SENT specimen after fracture test at 800˚C; (c) Fracture surface of SENT specimen after being tested at 800˚C showing different regions such as fatigue pre -crack and ductile crack growth. (a) (b) (c)