PSI - Issue 60

Prakash Bharadwaj et al. / Procedia Structural Integrity 60 (2024) 655–664 Prakash Bharadwaj / Structural Integrity Procedia 00 (2019) 000 – 000

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and load ratio (R). During these tests, a 3D Digital Image Correlation (DIC) technique has been used to evaluate the CPZ size under FCG loading. Here, the DIC evaluated von-Mises strain and the corresponding load hysteresis diagram has been used for sizing the CPZ. Subsequently, the experimentally evaluated CPZs are compared with that obtained from a 2D finite element simulation for plane stress conditions. 2. Material properties and specimen preparation A full compact tension specimen of thickness 25 mm and the rest of the dimensions are in proportion to thickness is fabricated according to ASTM standard E647-95a (1995) and is shown in Fig. 1.

Fig. 1. Full Compact tension specimen

This specimen is fabricated from a nuclear piping steel SA333Gr6 having yield and ultimate strength 290 MPa and 450 MPa respectively at room temperature. Young’s Modulus of elasticity is 204.8 GPa. A fabricated CT sample is prepared for DIC mounted FCGR test. Preparation of the sample is required for proper capturing of the strain field from the surface of the specimen. Fabricated CT samples have shining surfaces. First, cleaning of the CT samples has been carried out with acetone. After that, a coating of white paint is applied to the surface of the samples to avoid reflection from the shining surfaces. When white paint coating is completely dried, an inspection has been carried out to ensure that, there is no reflection from the shining surfaces of the sample. After confirmation, a black speckle pattern is made on the surface above the white paint coating, with the help of black paint spray. During the making of the black speckle pattern, it is ensured that very fine droplet is deposited on the surface of the

samples. The prepared sample is shown in Fig. 2(a). 3. Fatigue Crack Growth Rate (FCGR) Tests

The FCGR tests are carried out following ASTM E647 standard, on a servo-hydraulic universal testing machine having a capacity of 100 kN. These tests are conducted at the frequency of 10 Hz. During the data acquisition, test frequency and data acquisition rate was 0.1 Hz and 0.05s respectively. Tests are carried out in constant load amplitude and constant load ratio mode. The load maxima and load ratio of the tests are 8.5 kN and 0.1 respectively. FCGR tests are performed over a range of Δ K values, from 12.35 Mpa √ to 66.36 Mpa √ where the crack extended beyond the criterion of ASTM-E647 which ensures Small Scale Yielding (SSY) conditions (LEFM