PSI - Issue 41

Danilo D’Andrea et al. / Procedia Structural Integrity 41 (2022) 199–207 D’Andrea et al. / Structural Integrity Procedia 00 (2019) 000–000

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variation. The temperature variation has been evaluated as the initial temperature of the specimen minus the instantaneous temperature (ΔT= T 0 -T i ) and then filtered with the rlowess filter. In Fig. 3a is reported the temperature trend of the traditional AISI 316L specimen. In the initial part of the ΔT-t curve an initial linear trend of the temperature signal in clearly visible. Then the temperature deviates from linearity presenting a zero-derivative flex. It is possible to draw two linear regression lines, one for phase I and the other for phase II and to determinate the relative equations of the two straight lines. By solving the system of the two equations, it is possible to determine the coordinates of the meeting point of the two straight lines. The value of the limit stress determined by STM is equal to σ lim = 236±30 MPa. The same procedure can be applied to AM 316L specimen (Fig. 3b), where the same linear temperature trend is observed. For the three AM specimens the average value of the limit stress is equal to σ lim = 191±17 MPa.

(a)

(b)

Fig. 3. Temperature trend during static tensile test performed on AISI 316L specimens: a) Traditional; b) AM.

Table 2 reports the ultimate strength and the limit stress obtained for each tested specimen. As it is possible to observe, the ultimate strength is considerably higher for the traditional AISI 316L respect the AM one. At the same time, the limit stress, according to Risitano and Risitano (Risitano and Risitano (2013)) as the first stress level that introduces in the material the first irreversible damage, is higher for traditional material; however, it is not really far from the values reached by the AM material. It is evident how traditional AISI 316L exhibits better static tensile mechanical performances compared to the AM counterpart. Such characteristics can be addressed to the microstructure of the material.

Table 2. Test results for AISI 316L

Specimen type

No. Specimen σU [MPa] σlim [MPa] σU ave[MPa] σlim ave[MPa]

1

707

234

AISI 316L Traditional

2

709

266

714 ± 11

236 ± 30

3

727

207

1

370

203

AISI 316L AM (230W)

329 ± 74

191 ± 17

2

373

199

3

244

171