PSI - Issue 28

S. Henschel et al. / Procedia Structural Integrity 28 (2020) 1369–1377 S. Henschel et al. / Procedia Structural Integrity 00 (2020) 000–000

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3. Results and Discussion

3.1. Microstructure

After heat treatment, the microstructure consisted of a tempered martensite, see Figure 7. Furthermore, non-metallic inclusions are present. Previous studies (Seleznev et al. (2020)) utilizing the steel casting simulator already showed that these non-metallic inclusions are predominantly alumina inclusions.

3.2. Macroscopic behavior

Representative force / displacement curves of specimen tested with di ff erent loading angles α are shown in Figure 8. A macroscopic view on the fracture surface is given in Figure 9. It was observed that the curves show nearly linear elastic behavior until fracture. However, the fracture surfaces consisted of flat and slant areas. Hence, there was a mixture of plane strain and plane stress stress states in the specimen. The critical force, i.e. the maximum force increased with increasing α . Due to the rotation of the loading device with the specimen, the sti ff ness was reduced with increasing α .

3.3. Analysis with strain gauges

The results of the strain gauge measurement are shown in Figure 10 for pure mode I loading ( α = 0 ◦ ) and for α = 30 ◦ as examples. It was observed that K I could be reasonably described with the strain gauge signals. However,

Fig. 7. Microstructure of the investigated material: (a) tempered martensite; (b) non-metallic inclusions.

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Force / kN

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Fig. 8. Force / displacement curves of specimens tested at di ff erent loading angles α .