PSI - Issue 68

A.F Perez et al. / Procedia Structural Integrity 68 (2025) 439–445 A. F. Perez et al. / Structural Integrity Procedia 00 (2025) 000–000

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Table 3. Dimensions and characteristics of the CT samples tested. CT geometry Side grooves No Fatigue pre-crack Yes Width, [mm] 50 Thickness, [mm] 25 Net Thickness, % [mm] 25 Initial crack length, & [mm] 25 Ratio, & / [-] 0.5

2.2. Testing conditions Fracture toughness tests were carried out on three CT specimens at 600°C. All samples were pre-cracked to an initial crack length of 26 mm. The Direct Current Potential Drop (DCPD) method was used for the three tests to measure crack initiation and growth. The experimental protocol strictly followed the steps described in the ASTM E1820-23a standard (2023). A furnace was used to bring the samples up to temperature. To monitor their temperature, three thermocouples were installed on the specimens (one on each side and one underneath). For the last test, the Digital Image Correlation (DIC) method was implemented in addition to the DCPD method to analyse the deformation field around the crack tip on the CT sample. 3. Results 3.1. Tunnelling effect on fracture surfaces An example of the samples obtained after the tests is shown in Figure 1. A large zone of plastic deformation and shear banding is visible to the naked eye.

Fig. 1. (a) Example of a sample after the test; (b) Close-up of the crack tip area highlighting the plastic deformation zone (circled in red).

All three samples were then opened completely by fatigue as depicted in Figure 2. Table 4 summarizes the measurements and crack extension values for the three specimens: the maximum crack extension value, the area of the rupture zone and the average crack extension value. The latter is calculated by dividing the area by the sample thickness which is equal to 25 mm.

Table 4. Measurement of final crack extension on open samples. '() [mm] Crack area [mm 2 ] (*+,(-+ [mm] . 3.56 30.70 1.23 / 1.03 9.25 0.36 0 1.06 13.59 0.54