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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Fig. 5. SEM-images of the cyclic compression-compression 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. 3.2. Damage accumulation under cyclic tension-compression loading To analyze the load path-dependent damage evolution under tension-compression loading, additional experiments were conducted at a stress ratio of R = –1. In these tests, the evolution of damage was investigated over three load cycles between +450 MPa and – 450 MPa. The progression of the nominal stress over time is shown in Fig. 6a . Similar to the previously described experimental procedures, SEM images were also acquired during intervals in which the applied stress was held constant. These imaging intervals correspond to phases of constant load and enable reproducible monitoring of microstructural evolution. In the plots of nominal stress over time, these segments were cropped out to improve clarity and facilitate a more intuitive understanding of the loading sequence.

Fig. 6. Representation a) of nominal stress σ Ν over time for a tension-compression test and b) nominal stress σ Ν , damage proportion f D , sulfide proportion f S and the ratio of damage sulfide proportion F DS over time for the same tension-compression test.

Fig. 6b presents the evolution of the damage proportion f D , the manganese sulfide proportion f S , and the previously introduced ratio of damage to manganese sulfide proportion f DS over the course of the experiment. The progression of the damage proportion f D during the tension loading phases correlates well with the results from the previously