PSI - Issue 48

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

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The plate obtained at the end of the printing phase had sizes 170×70×8 mm×mm×mm and it contained 10 specimens. After the printing phase, the plate was milled and the thickness brought to 6.75 mm; successively, the plate was grinded and a final thickness of 6.65 mm was obtained. The plate with its final dimensions and the ten specimens is schematized in Fig. 1. The specimens were extracted from the plates by means of the Electrical Discharge Machining (EDM).

Fig. 1. Schematization of the printed plate with the main dimensions and numbers of obtained specimen. The printing direction was z.

In particular, one full specimen (n. 10) was used for metallographic analyses, for which the etching was carried out by using the Vilella reagent (1 g of picric acid, 5 ml of cloridric acid and 100 ml of ethanol). The other nine specimens were manufactured as Compact-Tension, C(T) specimens, with dimensions in according to ASTM E647 (2015) and characterized by different notch orientations as shown in Fig. 1. One of these nine specimens was used for the setup of the mechanical testing machine, four of these specimens (no. 2, 5, 6 and 8) were used for carrying out fatigue crack growth tests in air and the remaining four will be used in the near future for further evaluations. A schematic of an obtained C(T) specimen is reported in Fig. 2a together with its main dimensions. Each C(T) specimen was equipped with a CEA 06-032UW-120 Back-Face Strain-gauge (BFS) and with two Crack-Gauges (CG). Each CG was characterized by 20 filaments and by a distance of 0.254 mm between two adjacent filaments (Fig. 2b).

Fig. 2. (a) C(T) specimen extracted from the printed plate with its main dimensions. (b) positioning of two crack gauges and one back-face strain gauge on the generic C(T) specimen.

Each of the four specimens was subjected to a fatigue tension-tension test, according to the ASTM647 Standard and by means of an Instron 8502 testing machine, having a load cell of 20 kN. The applied fatigue load was characterized by maximum load of P ma x = 4500 N and a load ratio of R = 0.1. A pre-cracking phase was considered for all tests by avoiding the cycle counting until that the pre-cracking distance of about 1.3 mm.