PSI - Issue 68

Antti Järvenpää et al. / Procedia Structural Integrity 68 (2025) 619–625 Antti Järvenpääa et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 4. Method A: Ratio between the strength of the lattice structures and solid material in (a) compression; (b) tension.

3.3. Method B strength analysis In contrary to Method A calculations, where nominal cross-sectional area was used to calculate the stresses, true area was used in Method B to calculate the YS and E in individual struts. This analysis is used for FEM and for material quality analysis and optimization activities. Since the used area is smaller, both the calculated YS and E are larger than measured with Method A. In the most optimal case, we should see similar values than observed with solid material, but because of geometrical effects (surface roughness, manufacturing limitations, etc) and pronounced effect of porosity, the measured values are mostly below the values of the solid Ti6Al4V. The Fig. 5 shows both the compression (a) and tension (b) test results. Distinctly different kinds of trends can be seen in E’s between the load types, while the E in compressive loading tends to remain below 20% of the 110 GPa of solid Ti6Al4V with a decreasing trend as the relative density increases, the E in tension keeps increasing from ~30% up to 80% of the solid counterpart. The YS at relative densities of 0.4 and 0.5 is close to the reference value of the solid titanium both under compression and tension. A clear decrease in YS can be seen when decreasing the relative density down to 0.1. This can be attributed to a decrease in material quality when decreasing the strut thickness near the theoretical minimum values of the used SLM 280 HL printer. The strut thickness decreased at 25 µm steps from the value of 300 µm of the 0.5 relative density samples, and the strut thickness of the lowest density samples was 200 µm.

Fig. 5. Ratio between the strength of the lattice structures and solid material in (a) compression; (b) tension.

3.4. Tension – compression anisotropy (Method A) Fig. 6 shows the ratio between compressive and tensile yield strength (a) and Young’s modulus (b). Excluding the stochastic YS, all the curves show a steep slope as an indication of a significant relationship between the relative density and structural tension–compression anisotropy. In the stochastic structures, the YS anisotropy ratio remained around 1.25 for all the studied densities, showing higher compressive YS for all the structures. For the gyroid structure