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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3. Results and discussion 3.1. Comparison between TMPS gyroid and stochastic lattices

The comparison between gyroid and stochastic lattices at different relative densities showed better performance with gyroid structures across all densities (Table 1). The yield strength (YS) and Young’s modulus (E) were consistently higher than those observed with stochastic structures, but differences were higher in YS values than E’s. Behavior and trends depended on the load type and calculation method. The YS’s of the gyroid lattices were roughly 15% (compression) and 30% (tension) higher than the ones of stochastic lattices. Both lattice structures exhibited higher E in tension than in compression. Low compressive E can be considered beneficial for medical implant applications, where the implant development has been pursued to match the stiffness of the implant with Trabecular and Cortical bones to reduce the stress-shielding effect. On the other hand, the combination of low density and high tension stiffness is interesting for the general weight reduction of metallic structures.

Table 1. Static axial test results.

Structure

Method A

Method B

Tens. YS

Comp. YS

Tens. E [GPa]

Comp. E

Tens. YS

Comp. YS

Tens. E [GPa]

Comp. E

[MPa]

[MPa]

[GPa]

[MPa]

[MPa]

[GPa]

Gyroid – 0.1 Gyroid – 0.2 Gyroid – 0.3 Gyroid – 0.4 Gyroid – 0.5

51

50

4,9 9,9

2

499 656 665 841 798 357 507 562 569 658

497 800 764 863 706 445 607 653 740 744

49,1 59,4 68,1 76,9 88,8 36,1 43,3 69,6 89,8 77,7

20,0 20,1 17,4 15,0 13,3 16,3 17,5 15,6 13,6 11,9

113 197 335 402 100 163 216 314 36

118 222 336 494 121 198 286 389 46

4,1 5,3 6,1 6,5 1,6 3,5 4,4 5,1 5,4

20,7 34,5 43,4 10,6 20,8 33,6 36,9 3,6

Stochastic – 0.1 Stochastic – 0.2 Stochastic – 0.3 Stochastic – 0.4 Stochastic – 0.5

3.2. Method A strength analysis Two different calculation methods were used to analyze the compression and tension test data. Method A generally describes the structural performance of the lattices (nominal cross-section) and Method B is used to analyze the strength of the lattice struts (true area). Based on Method A (Fig. 4), the measured yield strength of the TMPS gyroid lattices was 51–402 MPa (tension) and 50–494 MPa (compression) for relative densities from 0.1 to 0.5, respectively. Structural strength is impaired systematically and significantly as the level of porosity increases (tension yield strength of the solid LPBF structure was 827 MPa). Quite similarly we can see a drop in elastic modulus from the 110 GPa of the solid Ti6Al4V down to 43 GPa (tension) and 6.4 GPa (compression) as the relative density decreases to 0.5. Further decrease in relative density down to 0.1 decreased the Young’s modulus down to 4.9 GPa (tension) and 2.0 GPa (compression). The strength difference between the gyroid and stochastic lattices was more pronounced with high relative densities. With low densities, even some equally strong structures were seen between two lattice types. The trend was different for the E, where the greatest difference was observed with the lowest relative density (gyroid was roughly 30% stiffer). Both structures were significantly (E +300%) stiffer in tension than in compression, but the strength was lower in tension. For the stochastic structures, 20% lower YS values were measured in tension than in compression. The difference for the gyroid structures was only 6%, showing more isotropic strength properties.