PSI - Issue 76

Davide D’Andrea et al. / Procedia Structural Integrity 76 (2026) 151–158

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of -0.649 K. STM results for quasi-static monotonic tensile tests are reported in Table 2. All the specimen subsets show a large scatter, with an estimated limit stress of 26.2±2.9 MPa.

Figure 3. STM representation of S_PA12_X_03.

Table 2. Limit stress estimation according to STM for X and Y specimens set.

STM limit stress [MPa] 29.0

Test ID

S_PA12_X_01 S_PA12_X_02 S_PA12_X_03 S_PA12_Y_01 S_PA12_Y_02 S_PA12_Y_03 Average value

26.1 26.5 28.3 20.7 26.9 26.2

Standard deviation

2.9

3.2. Constant amplitude fatigue tests

Fatigue life of SLS PA12 has been assessed through a stress-controlled constant amplitude fatigue test campaign on both specimens sets, imposing the maximum stress with a stress ratio of R= 0.1. Results are reported in a bi logarithmic maximum stress vs. number of cycles to failure graph in Figure 4, where the printing direction of the specimens, X (red marker) and Y (blue marker), do not affect the fatigue life; indeed, the markers are well aligned along the same regression line , obtained by fitting the Basquin’s law (purple line). In the same graph fatigue tests by Rosso et al., (2020), with a stress ratio of R= 0, are reported with green diamonds and fitted with Basquin’s law (green line). This comparison demonstrated worse fatigue behaviour for PA12 specimens printed along the Z direction, since the S-N curve for X and Y specimens is characterized by a higher inverse slope k and a higher fatigue limit prediction, estimated at N=10 6 cycles, equals to 29.3 MPa, while the fatigue limit reported by Rosso et al. is equal to 16.8 MPa. Comparison with Rosso ’s work was possible even if tests were performed at a different stress ratio, since S-N curves are expressed in terms of maximum stress as explained by Ezeh and Susmel, (2019).