PSI - Issue 66

30 Carl H. Wolf et al. / Procedia Structural Integrity 66 (2024) 26–37 Carl H. Wolf, Sebastian Henkel, Christian Düreth, Maik Gude and Horst Biermann / Structural Integrity Procedia 00 (2025) 000–000 5 (a) (b)

Figure 3: Schematic representation of the loading of the specimen under (a) uniaxial and (b) biaxial loading with representation of the compression stamp arrangement. The force along the specimen axis was applied cyclically, the force normal to the crack growth direction in (b) was statically applied.

After the cyclic test, a digital image correlation (DIC) was performed using GOM ARAMIS v6.3.1 (GOM GmbH, Braunschweig, Germany) with a facet spacing of 0.15 mm. The analysis was done in several steps. First, the image with the maximum shear stress was determined from each image sequence. Subsequently, the crack tip was determined in these image sequences using CrackPy [7]. With CrackPy, it is also possible to detect the crack tip of closed cracks, cf. Figure 4. This is necessary due to the compressive loading normal to the crack. In the final step, the individual image sequences were analyzed using DIC, i.e. the displacement field around the crack tip during cyclic loading was determined. Finally, the energy release rate was determined from the displacements. For this purpose, a virtual measuring clip method was used. (a)

(b)

Figure 4: Example of a crack tip determined using CrackPy on a specimen subjected to F compression = 1 kN and F tension = 2.75  2.25 kN. (a) Image at maximum shear stress and (b) superposition of the image from (a) with the crack tip determined using CrackPy.