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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2.2. Static tensile and fatigue tests Three lattice specimens were tested in static tensile tests at room temperature (RT), -60 °C and 200 °C as shown in Table 1. A servo-hydraulic testing machine (Instron 88R8502) with an environmental chamber was used. An extensometer (Instron 2620-602) with a gauge length of 50 mm was used to measure the displacement. Speed of testing was controlled by the extensometer with a displacement rate of 1.0 mm/min. Temperatures were measured on the specimen surface near the gauge section using thermocouples. The tests were started when 15 minutes passed after the temperature reached the testing condition. Total of seven lattice specimens were tested in fatigue tests at RT and 200 °C under load-controlled conditions as shown in Table 1. The same testing machine, environmental chamber and extensometer as those in the static tensile tests were used. A loading frequency was 10 Hz, and a load ratio R was 0.1. Three different loading values were applied at RT, and four different loading values were applied at 200 °C (see Table 1). Table 1 also displays “nominal” stress values in each test. These stress values were calculated based on an area of the minimum cross section of the lattice structure in the gauge section which is 121 mm 2 (see Fig. 1(c)). The tests were started when 15 minutes passed after the temperature reached the testing condition. The tests were terminated when the cycle numbers reached 1×10 7 cycles (run-out). Figure 1(c) shows the experimental set-up of the fatigue tests using the lattice specimens. Three cylindrical specimens were tested in fatigue tests at RT under load-controlled conditions for comparison with the lattice specimens, as shown in Table 1. A servo-hydraulic testing machine (Instron 8802) was used. A loading frequency was 10 Hz, and a load ratio R was 0.1.

Table 1. List of experiments

Test type

Specimen

Temp. [°C]

Load amp. [kN]

Mean load [kN]

Stress amp, σ a [MPa]

Mean stress [MPa]

Fatigue life [cycle]

Static tensile Static tensile Static tensile

Lattice Lattice Lattice

RT -60 200 RT RT RT RT RT RT 200 200 200 200

- - -

- - -

- - -

- - -

- - -

Fatigue Fatigue Fatigue Fatigue Fatigue Fatigue Fatigue Fatigue Fatigue Fatigue

Cylindrical Cylindrical Cylindrical

2.302 2.021 1.437 8.650 6.150 3.700 6.150 4.950 3.700 1.750

2.813 2.470 1.757 7.517 4.522 7.517 6.050 4.522 2.139 10.572

81.4 71.5 50.8 71.5 50.8 30.6 50.8 40.9 30.6 14.5

99.5 87.4 62.1 87.4 62.1 37.4 62.1 50.0 37.4 17.7

51,264 122,259 801,963

Lattice Lattice Lattice Lattice Lattice Lattice Lattice

2,725

31,163 347,229

4,837

94,741 554,502

Run-out

3. Results and discussions 3.1. Static tensile tests

Figure 2(a) shows load-displacement curves obtained by the static tensile tests of the lattice specimens at RT, - 60 °C and 200 °C. At RT, the maximum load and displacement values were about 26 kN and 0.5 mm, respectively. When the temperature decreased from RT to -60 °C, the maximum load value increased to about 28 kN whereas the maximum displacement unexpectedly remained almost the same value, 0.5 mm. On the other hand, when the temperature increased from RT to 200 °C, the maximum load value drastically decreased to about 15 kN whereas the maximum displacement significantly increased to 1.7 mm.