PSI - Issue 47

Jan Patrick Sippel et al. / Procedia Structural Integrity 47 (2023) 608–616 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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site with slight variations.

Fig. 3. Roughness measurements of AISI 52100 specimen via confocal microscopy: Measurement positions (left) and resulting Rz values (right).

To reduce these variations and therefore obtain more robust roughness values, circular measurements around the crack initiation site were performed, with their respective positions displayed by the red lines in the left and the medium roughness values along these red lines shown as the data points connected with the full line on the right. As expected, the variations are reduced and increasing roughness with increasing crack length is evident for the circular profiles as well. Figure 4 shows the analogous procedure for the AISI 4140 specimen with the values shown as the blue symbols on the right.

Fig. 4. Roughness measurements of AISI 4140 specimen via confocal microscopy: Measurement positions (left) and resulting Rz values (right).

While also observing an increasing roughness trend with increasing distance to crack initiation site similar to the roughness development of the AISI 52100 specimen, in case of the AISI 4140 Specimen significantly reduced roughness values are observed in the darker parts of the heterogeneous fracture surface. Strikingly the significantly reduced values of the longitudinal as well as circular profiles in those darker areas correspond approximately with the respective roughness values measured inside the fisheye of the specimen. To understand these drops in roughness values at the late crack propagation stage, a fracture surface morphology analysis using SEM is performed.