PSI - Issue 38

W. Radlof et al. / Procedia Structural Integrity 38 (2022) 50–59 W. Radlof et al. / Structural Integrity Procedia 00 (2021) 000 – 000 = , − 0.5( 1 + 2 )

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3.3.1. Bending loading The temperature curves of the struts ( ∆ ) as well as the potential curve are plotted versus the fatigue life in Fig. 7 exemplarily for a 50% porosity fatigue loaded bending sample. Fig. 7b clearly shows peaks in the temperature curve at more than approx. 90% of the fatigue life. At these points, hotspots are visible in the temperature field images of the lattice structures. The hotspots occur at the time of strut failure, as shown in Fig. 7c – II-V. Furthermore, a small temperature peak was detected at 74% fatigue life, where a hotspot is also visible in the temperature field image (Fig. 7a, c – I). From the diagrams in Fig. 7 it can be seen that each temperature peak, which is accompanied by a local failure at a strut, occur while the potential also rises. This suggests that an increase in potential could be related to the failure of the lattice structure. Moreover, since the temperature measurement is a local failure detection method, the potential drop method could be related to the failure also of inner struts, which was already seen in Fig. 5 by the micrograph analysis. In addition, a slight temperature increase can usually be detected during the fatigue life, which indicates increasing global damage. However, the potential drop method is better suited for the characterization of the global failure behavior of the lattice structure due to the detection of the failure of inner struts, whereas a specific local strut failure can be identified with the temperature method. Additionally, the results of the thermography method were exemplified here, where local damage could be detected. This was not the case for all samples examined.

3.3.2. Torsion loading The temperature curve, the progression of the potential as well as the temperature field images are shown versus the fatigue life exemplarily for a 50% porosity torsion loaded sample in Fig. 8. It becomes obvious that the temperature at the struts, where failure occurs at the end of the test, increases successively ( ∆ 1 ), while no increase in temperature can be seen at the strut where no failure occurs ( ∆ 2 ). However, in all samples examined, no hotspots could be identified that could be associated with local cracks or strut failure. The temperature curve also only rises substantially at a fatigue life when the potential difference also rises clearly. From this, no reliable Fig. 7: Fatigue behavior of an exemplarily 50% porosity lattice structure tested under bending loading. (a, b) Cyclic deformation behavior based on the change of the potential and temperature of the analyzed strut-lines with selected extracts at different fatigue life ranges. (c) Temperature field images of the lattice structure at different states of the fatigue life.