## 3 Materials and Methods  
The feasibility of a successful damage model calibration using only a tensile testing machine for the experiments is investigated and proved employing, along with conventional round bar and round notched bar samples (Figure 1), two types of multiaxial test specimen geometries proposed by [PERSON] [32] and [PERSON] [33], which can induce combined tensile-shear stress states in the material. The round bar geometry is required for both elasto-plastic characterization and for fracture at medium triaxiality, while the notched geometry is effective for stress concentrations and high triaxialities [42; 43]. Shape, dimensions, and actual pictures of the shear-tension specimens are shown in Figures 2 and 3. These geometries are slightly modified and simplified with respect to the original ones proposed by the authors, as a result of an optimization analysis ([PERSON] [44] and [PERSON] [45]). Through the [PERSON]'s specimen, different shear-tension stress states can be generated due to two central holes that can be machined rotated clockwise by an angle alpha (\(\alpha\)), as shown in Figure 2a. The larger the \(\alpha\), the greater the tensile component of the stress state with respect to the shear component; therefore, varying the \(\alpha\) angle different pairs of \(T_{\alpha\alpha}\) and \(X_{\alpha\alpha}\) can be obtained, which are all seen to fall in a low triaxiality regime. Instead, the [PERSON]'s specimen is machined in a unique geometry, and a different direction of the applied load is the key factor to inducing distinct tensile-shear stress states. Using a suitable clamping system, reported in Figure 4, the specimen can be rotated with respect to the axial loading direction of the testing machine by fastening the clamps to the testing machine grips at different angles through bolted connections, thus changing the correspondingly generated stress state. In fact, the configuration with alpha equal to \(0^{\circ}\) induces a stress state close to pure shear stress, whereas the angles between 15-75\({}^{\circ}\) produce a mixed tensile-shear stress, instead a loading angle of \(90^{\circ}\) corresponds to a plane strain condition. In this work, two configurations with \(\alpha\) equal to +10\({}^{\circ}\) (Pos10) and +30\({}^{\circ}\) (Pos30) were selected for the [PERSON]'s specimen shown in Figure 2a, while for the [PERSON]'s specimens, a configuration with loading angle equal to \(0^{\circ}\) (Mohr00) and +15\({}^{\circ}\) (Mohr15) was chosen (Figure 4). In all four cases, mixed tensile-shear stress states were obtained. Two materials were investigated, particularly a high-strength 17-4 PH steel alloy and a Ti6 Al4V titanium alloy. Their behavior has been considered as isotropic, as shown in various literature studies [46; 47]. Their experimental true stress and true strain curves are reported in Figure 5, together with a corresponding Hollomon's power law fit. It is worth noting that only the initial part of the experimental curves, around up to a true strain of 0.15, are determined experimentally, while the behavior conventionally chosen up to a large strain of 1.0 is derived numerically by means of an inverse finite element procedure with the aim to minimize the error between the experimental and numerical global response (force-displacement). Specifically, for 17-4 PH, the strength coefficient \(K\) and the hardening  
Figure 1: Round bar (RB) specimen and round notched bar (RNB) specimen. Figure 2: (a) Technical drawing of [PERSON]’s specimen with detail for \(\alpha=10^{\circ}\) (Pos10) and \(\alpha=30^{\circ}\) (Pos30) configurations; (b) machined sample for Pos10 configuration. exponent are set equal to 1420 MPa and 0.12, while for Ti6 Al4V, they are set equal to 1305 MPa and 0.08.