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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3.3. Fracture surface morphology analysis via SEM To better understand the visual differences as well as the different roughness values of the fracture surfaces described above, the microstructure was analyzed using SEM. Figure 5 shows nine secondary electron (SE) images of equal magnification along the crack path of the AISI 52100 specimen, with their respective positions being marked by red rectangles and labeled with the respective letters in the right overview image.

Fig. 5. Fracture surface morphology of AISI 52100 analyzed via SEM and their respective position.

Inside the fisheye, close to the failure inducing non-metallic inclusion a fatigue fracture surface with the characteristically smooth surface topography is observed. Outside the fisheye a ductile force fracture surface with dimples or honeycomb like structures is found. However, no change in the crack propagation regarding the fracture surface morphology outside the fisheye is evident and the increase in roughness described above can be explained with the trend for increasing fracture surface topography shown in the SE images from f to i. Therefore, we can assume that the SIF at the border of the fisheye correlates with the fracture toughness of the material resulting in unstable crack propagation and the observed final force fracture. Figure 6 is analogous to Figure 5 but for the AISI 4140 specimen. With nine SE images of equal magnification displayed in the grid to the left and their respective positions marked in the overview image on the right.

Fig. 6. Fracture surface morphology of AISI 4140 analyzed via SEM and their respective positions.