PSI - Issue 53

Venanzio Giannella et al. / Procedia Structural Integrity 53 (2024) 172–177 Raffaele Sepe / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 1. General overview: from the manufacturing of samples, to the preparation and instrumentation of the C(T) specimens, to the tests; highlight of the three measurement systems in blue: (a) crack gauge, (b) strain gauge, (c) clip gauge.

Fig. 2. Specimen geometry with highlights of the 3 building directions and of the applied fatigue load.

3. Results and discussion Some of the samples manufactured by EBM were shown in Figure 3. For a better comprehension, the building direction was highlighted as well as the specimen labels that were always positioned at the front faces, i.e. the faces where the notches were made (see also Figure 2). Specimens were tested in laboratory conditions by considering the setup shown at the right side of Figure 2. An example of a fractured specimen is shown in Figure 4. As expectable, a pure Mode-I propagation was observed, according to the test setup. Cycle counting started after a pre-cracking phase that consisted in discarding the first 2 mm of crack propagation. The three measurement systems were continuously used during the tests to monitor the propagation to derive a cross-comparison in terms of crack lengths during the fatigue cycles. The comparison among these outcomes was good and was not reported here for sake of brevity; only the results obtained by means of the back-face strain gauge were reported in Figure 5. The back-face strain method consists in measuring the variation of the strain at the back face along the propagation and is used to derive the crack length through the formulae in Eq. 1 (Newman et al., 2011; Califano et al., 2023). In Eq. 1, is the Young’s modulus, ε is the strain measured at the back face, is the specimen’s width, is the thickness. The coefficients for 0.2<