PSI - Issue 68

Shiyu Suzuki et al. / Procedia Structural Integrity 68 (2025) 596–602 S. Suzuku, N. Tsushima / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 2. (a) Load-displacement curves obtained by static tensile tests; (b) Optical observations after fracture.

Figure 2(b) shows results of optical observations of the specimens after the fracture. For the specimens tested at RT and -60 °C, it can be seen that single main cracks propagated in the lattice structure resulting in the macroscopic fracture. On the other hand, in the specimen tested at 200 °C, two main cracks with an equivalent size propagated from two opposite sides of the lattice structure being accompanied by an apparent plastic deformation. From the above results, in the static tensile tests, decreasing temperature from RT to -60 °C results in a higher strength and the equivalent ductility whereas increasing temperature from RT to 200 °C results in a lower strength

and a higher ductility. 3.2. Fatigue tests at RT

Figure 3(a) shows a S-N diagram obtained by the three fatigue tests using the lattice specimens at RT. The vertical axis is the stress amplitude, σ a , and the horizontal axis is the fatigue life, N f . The exact numbers of the fatigue lives of these specimens are also provided in Table 1. Figure 3(b) shows load-displacement curves of one cycle at the half life, N f /2, of each lattice specimen along with the curve obtained by the static tensile test (see Fig. 2) for reference. From Fig. 3(b), it can be seen that in all of the three load conditions, the hysteresis is quite small, and the elastic deformation is dominant. We assume that in these tests, the fatigue behavior is so-called “high cycle fatigue”. Thus, Basquin’s law was applied to these tests’ results, which shows a good correlation between the fitted curve and the experimental fatigue lives as shown in Fig. 3(a).

Fig. 3. (a) S-N diagram at RT; (b) Load-displacement curves of lattice specimens at the half life, N f /2.