PSI - Issue 53

Andrea Zanichelli et al. / Procedia Structural Integrity 53 (2024) 3–11 Author name / Structural Integrity Procedia 00 (2019) 000–000

9

7

The quality of the present results can be statistically interpreted by employing the root mean square error method (Zanichelli et al. (2022)), thus confirming quite accurate results for uniaxial tests, since the values of T RMS are lower than 2 (Figure 3). In the case of biaxial loading, a higher value of T RMS is obtained, but statistical considerations are quite unreliable in this case due to the very small number of specimens for each loading configuration.

5.0

Wang et al. (2021) Present study

4.0

3.0

2.0

T RMS

1.0

0.0

Axial, R=-1

Axial, R=0

Torsional, R=-1

Biaxial

Fig. 3. T RMS values related to both the present analytical methodology and the MWCM (Wang et al. (2021)) for the plain specimens.

The results available in the literature (Wang et al. (2021)), determined by employing a different critical plane based multiaxial fatigue criterion (named Maximum Wöhler Curve Method (MWCM)), are also reported in Figure 3 for comparison. A similar accuracy is noticed by using the present methodology and the MWCM criterion, for all fatigue tests; in particular, a higher accuracy is gained by applying the present methodology with respect to that deduced through the MWCM criterion. Therefore, it can be concluded that a high level of accuracy is obtained by employing the present analytical methodology, in terms of fatigue life assessment of plain specimens made of the examined additively manufactured AISI 316L stainless steel. As a matter of fact, a T RMS overall value equal to 1.98 is obtained in such a case. 4.2. Notched specimens As far as the notched specimens are concerned, the procedure described in sub-Section 2.2 is applied. Note that an angular increment 15 α ∆ = ° has been fixed. Furthermore, regarding the methodology here employed and presented in details in Section 2, some theoretical concepts need to be emphasized. In particular, the stress state within the notched AM component is computed by means of a set of closed-form solutions available in the literature (Filippi and Lazzarin (2004); Zappalorto et al. (2010)). Note that, in order to apply such solutions, some characteristic parameters related to the notch geometry and the remote loading conditions need to be set. Among such parameters, the stress concentration factors, K t , characterising each test configuration examined, have been taken from the corresponding diagrams available in the work by Pilkey and Pilkey (2007) and, more precisely, they are equal to: 4.80 (axial loading) and 2.50 (torsional loading), for sharp notched bar of circular cross section; 1.75 (axial loading) and 1.30 (torsional loading), for circular notched bar of circular cross section; 1.30 (axial loading) and 1.12 (torsional loading), for blunt notched bar of circular cross section. The comparison between the calculated and the experimental number of loading cycles to failure, N cal and N exp , respectively, is shown in Figures 2(b), (c) and (d) for the specimens characterised by a sharp notch (root radius r=0.07 mm), a circular notch (root radius r=2 mm) and a blunt notch (root radius r=5 mm), respectively. The data in red are related to the pure axial fatigue tests, whereas those in black are related to the biaxial (that is, combined