PSI - Issue 77

L.A. Lingnau et al. / Procedia Structural Integrity 77 (2026) 26–33 Author name / Structural Integrity Procedia 00 (2026) 000–000

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It is assumed that the projected area of the manganese sulfide remains constant during the experiment. Consequently, an increase in f DS is interpreted as an increase in damage. During the first loading cycle, the damage parameter f DS increased by 9.5 %, indicating a significant accumulation of damage within the initial cycle. After three loading cycles, the damage was 13.8 % higher compared to the initial state. This demonstrates that subsequent cycles also contribute to damage evolution and lead to progressive damage accumulation. However, it is important to emphasize that the first loading cycle contributes most significantly to the overall damage accumulation and thus has the greatest influence on the observed damage progression. Due to the plastic deformation of the material, this observation can also be related to the findings of Hering & Tekkaya, 2020.

Fig. 4. SEM-images of the cyclic tension-tension test a) for the initial state, b) for a nominal stress of 450 MPa in the first loading cycle and c) for the final state; representation of the corresponding segmented image sections d) for the initial state, e) for a nominal stress of 450 MPa in the first loading cycle and f) for the final state. Comparable analyses were also performed for the compression-compression loading experiments. For this purpose, SEM images were taken at corresponding locations on the specimen, specifically at a selected manganese sulfide, at 0 MPa and 450 MPa during each loading cycle. Fig. 5a shows the initial state, Fig. 5b the state after the first loading cycle, and Fig. 5c the final state at the end of the experiment. The manganese sulfide marked in red again serves as a reference point for damage tracking in Fig. 5d –f . As in the tension-tension tests, the ratio of damage to manganese sulfide proportion f DS was used as a normalized damage metric. In contrast to the tension-tension loading experiments, no significant increase in the damage parameter f DS was observed under compression-compression loading. The value remained nearly constant throughout the loading cycles. It should be noted, that these investigations were limited to surface observations. Damage mechanisms such as decohesion between the manganese sulfide and the matrix, which may occur within the bulk of the material, could not be captured using surface imaging alone. Nonetheless, it was quantitatively confirmed that cyclic tension-tension loading has a considerably greater influence on damage accumulation compared to cyclic compressive loading.