PSI - Issue 42

Hasan Saeed et al. / Procedia Structural Integrity 42 (2022) 967–976 Hasan et al./ Structural Integrity Procedia 00 (2022) 000 – 000

972

6

a 0 = 311 μ m

Fusion line

208 μ m wide

K-Weld

Notch

5 mm

200 μ m

Fig. 6. (Left) Etched specimen revealing the K-weld and location of the notch at the fusion line. (Right) Notch dimensions after electropolishing.

Measurement of notch dimensions before and after electropolishing (for quality control) was performed using a Keyence VR-5200 wide-area 3D measurement system. Strain gauges of base length 7 mm and gauge length 3 mm were installed at the back-face of the SENB specimens (with the center of the strain gauge aligned with the mid section of the SENB specimen). 3.2. Determination of crack size from DCPD As a benchmark to evaluate the crack growth, the potential drop across the region of interest (i.e., the fatigue crack) during the tests was measured according to the schematic overview shown in Fig. 7, using a dual channel nano voltmeter.

Fig. 7 SENB-4P fatigue testing (Left), and schematic of instrumentation and test setup (Right). For the specimens reported in this paper, a constant current of 54 A was applied through current pins attached to the side faces of the specimens. The potential drop across the region of interest is a function of cross sectional dimensions and − , applied current , material conductivity , and probe positioning. As the primary goal is to relate potential drop with / , it is important to account for the effects of the other parameters (current density, conductivity, probe positioning). Although the delivered current is constant, the effective applied current through the region of interest can vary as the specimen is not electrically isolated from the test setup (i.e., there is a variable current leakage − ). To compensate for this discrepancy and potential changes in material conductivity during the test (e.g. due to temperature variation), preference is given to the dual probe technique in which the potential drop at the region of interest is normalized based on a reference measurement, which also accounts for changes in and .