PSI - Issue 28

Anja Gosch et al. / Procedia Structural Integrity 28 (2020) 1184–1192 Anja Gosch/ Structural Integrity Procedia 00 (2019) 000–000

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set‐up 2

set‐up 1

set‐up 3

Figure 1. The three testing set-ups used: Microscope (Microscope 1 vs. Microscope 2), IRT (Microscope vs. IRT) and DIC (Microscope vs. DIC).

2.3. Data evaluation from the IRT and DIC measurements The crack length evaluation was defined for each testing set-up separately. In the case of the travelling microscope the crack length was measured from the initial crack length (crack tip after the notching procedure) to the growing crack tip during the experiment. For the IRT set-up, the crack length was determined via the remaining ligament length, which is defined as the distance between the hottest point and the specimen end, as shown in Figure 2 .

Figure 2. Determination of the crack length in the IRT image through measuring the remaining ligament length (W-a).

The hottest point on the specimen surface is assumed as crack tip, however, this testing set-up is strongly influenced by the size of the plastic zone. For the DIC evaluation, the software GOM correlate professional 2016 (GOM GmbH, Braunschweig, Germany) was used. DIC measurements are highly influenced by the speckle size and the plastic deformation in front of the crack tip, which can lead to a disappearing deformation and strain field. Therefore, several methods exist to determine the crack advancement in combination with the obtained strain or