PSI - Issue 48

America Califano et al. / Procedia Structural Integrity 48 (2023) 238–243 Califano et al / Structural Integrity Procedia 00 (2019) 000 – 000

242

5

Fig. 4. Actual equipped C(T) specimen brought to failure during a fatigue test.

As aforementioned, the data collected through the BFS and the CGs have been used to calibrate the Newman Johnston equations and find the material’s Young’s modulus. Therefore, the found value of the Young ’s modulus is the one that makes the BFS and CG data match with each other. For the sake of simplicity, here only the results for specimens 2 and 5, characterized by different crack orientations (Fig. 1), are reported. The crack-length vs. number of cycles curves for the two specimens are reported in Figs. 5a and Fig. 5b, respectively.

Fig. 5. Crack length vs. number of cycles curves obtained for (a) specimen n. 2 and (b) specimen n. 5, by means of data collected by the crack gauges (red curves) and by the back-face strain-gauge (black curves).

The black curve represents the crack length measured by the BFS, while the red curve and squares represent the crack length data obtained through the CGs. By calibrating those curves, Young ’s modulus E = 165000 MPa has been obtained for both specimens. At this point, the crack-growth after pre-cracking has been assessed and it is shown in Fig. 6 for specimen no. 2 (red curve) and for specimen n. 5 (blue curve). The number of cycles to failure ( N f ) are reported in Table 2. Analysing both Fig. 6 and Table 2, it can be noticed that the two specimens have almost overlapping crack-growth fatigue behaviour, regardless of the crack orientation. The reason behind this is that alhough specimen 2 and specimen 5 have different crack orientations, cracks themselves lay in the same plane. As a matter of fact, from Fig. 1 it can be noted that the cracks lay in the xy plane, which is characterized by a less heterogeneous macrostructure (Fig. 3a). However, this could not have brought to a priori conclusions as, in general, specimens obtained by AM are not only anisotropic but heterogeneous as well. Finally, the preliminary obtained results showed that, for the considered material, obtained by means of SLM, the crack orientation does not affect the material properties (i.e., Young’s modulus) and the crack -growth behaviour.

Table 2. Number of cycles to failure ( N f ) for the two selected specimens Specimen N f 2 133544 5 130427