## 3 Materials and Methods
These alloys have already been extensively characterized in previous works by some of the authors [48; 49; 50], in which different damage models were calibrated testing more conventional specimens, specifically at least employing a set of round bar (RB), round notched bar (RNB), plane strain (PS), and torsion geometries (Tors), the last requiring a torsion capable machine for the test to be run. The values of triaxiality \(T\), deviatoric parameter \(X\), and plastic strain at failure obtained in these works were used to evaluate the fracture surface, to be considered as a benchmark for the comparison with fracture surfaces calibrated here by testing the [PERSON] and Mohr's specimens, which should prove to be equivalent in terms of ductility prediction effectiveness, therefore being suitable substitutes of other multiaxial specimens that require a more complex experimental setup. An MTS servo-hydraulic tensile machine with a maximum axial load of 250 kN and a 150 mm stroke was used to run the tests in control of displacement. Three repetitions were performed for each configuration of the [PERSON] (+10\({}^{\circ}\), +30\({}^{\circ}\)) and [PERSON]'s (0\({}^{\circ}\) and 15\({}^{\circ}\)) specimens. Subsequently to the experimental campaign, a finite element analysis (FEA) for each specimen was set up, using the commercial finite element code Ansys, to evaluate the accumulated equivalent plastic strain as well as the triaxiality \(T\) and deviatoric parameter \(X\) in the critical zone of the samples, up to fracture. A quasi-static non-linear structural  
Figure 4: [PERSON]’s specimen: clamping system to be connected to the test machine grips by screw connections. All seven possible pulling directions are reported, with the loading direction used at 0\({}^{\circ}\) (Mohr00) and 15\({}^{\circ}\) (Mohr15) highlighted by dashed circle. Figure 3: [PERSON]’s specimen: (**a**) technical drawing; (**b**) machined sample. analysis was set up; in particular, Ansys Workbench and Mechanical APDL platforms R2022 were used to simulate [PERSON] and Mohr tests, respectively. The experimental constitutive laws up to large strain of 17-4 PH and Ti6 Al4V reported in Figure 5 were implemented. Figure 6 shows the mesh size and the applied displacements and constraints; for the [PERSON]'s specimens, the used pulling directions are highlighted. To validate the FEA, for the shear-tension tests, a digital image correlation (2D-DIC) analysis was employed to compare the distribution of equivalent plastic strain obtained numerically with that evaluated through the optical technique. The following list summarizes the combinations of tests that were used as input for the successive calibration of the damage models:  
1. Conventional specimens (RB, RNB, PS, and Tors), from [49; 50];
2. [PERSON]'s specimens (RB, RNB, Pos10, and Pos30);
3. [PERSON]'s specimens (RB, RNB, Mohr00, and Mohr15);
4. [PERSON] and [PERSON]'s specimens (RB, RNB, Pos10, Pos30, Mohr00, and Mohr15);
5. All tests (RB, RNB, PS, Tors, Pos10, Pos30, Mohr00, and Mohr15). Figure 5: 17-4 PH and Ti6 Al4V experimental stress–strain curves, with corresponding power law fit. The maximum value of 1.0 is conventionally chosen and represents the nominal true plastic strain. Figure 6: Mesh size, applied displacements, and constraints for the [PERSON] and [PERSON]’s specimens. For the [PERSON]’s sample, the pulling directions that were actually tested (\(0^{\circ}\), \(15^{\circ}\)) are reported. In particular, the calibration through (1) was used as a reference, being based on conventional tests, while the calibration through (5) relying on the highest number of data is expected to be the most accurate. Once all the calibrations were carried out, a comparison between all the fracture surfaces was put forth to assess the prediction resulting from the different tuning scenarios.