PSI - Issue 56

Radim Halamaa et al. / Procedia Structural Integrity 56 (2024) 111–119 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

115

5

Fig. 3. Scheme of specimen geometry.

For fabricating specimens, the Renishaw 3D printer, namely AM400 type, was used. All the specimens were tested in as-built state. The most important printing parameters used during the AM process are reported in Table 1. The 90° orientation of the sample indicates its position in the printer chamber during the production process. The specimens were printed with 350 W laser power, a scanning speed of 1150 mm·s -1 and a layer thickness of 30 µm. The 'Meander' scanning strategy was applied, which is the most used strategy for specimens with small cross sections. During fabrication, the chamber was filled with argon with purity 5.0 to prevent oxidation. The building platform was preheated to 170 °C to reduce residual stresses during the AM process.

Table 1. Printer setting parameters for the production of fatigue specimens. Specimens orientation 3D printing strategy Laser power (W) Laser rate (mm  s -1 ) Layer thickness (µm)

Preheating of building platform (°C)

90°

“meander”

350

1150

30

170

3.2. Low-cycle fatigue testing All the three loading cases were realized using the Epsilon Tech 3550 biaxial extensometer for controlling the axial/shear strain in the gauge part (25 mm gauge length). Time-periods in the tension-compression and pure torsion tests were 6 s and 14 s respectively. In the non-proportional loading case, the strain rate was 1 %/s. Equivalent strain amplitudes in the middle-life were: 1.5 % (push-pull), 1.75 % (torsion) and 1.25 % (nonproportional). Two cameras with a resolution of 2.3 Mpx and a frame rate of 20 fps were used in a 3-D measurement arrangement. 4. Results This chapter presents the results obtained by the accelerated fatigue test evaluation methodology. The resulting cyclic stress-strain curves are compared with the data obtained by conventional approach (ASTM E2207). 4.1. Torsion case In the pure torsion case, the symmetric shear strain cycle generated the waveform of the response quantity (torque). The time history of torque in the mid-life of the specimen is shown in Fig.4(a), whereas the corresponding