PSI - Issue 23

Petra Ohnišťová et al. / Procedia Structural Integrity 23 (2019) 469 –474 Petra Ohnišťová et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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3. In-situ mechanical testing and results

The in-situ mechanical testing of the specimen was performed with a special geometry allowing uni-axial loading. Profiles of the specimens were manufactured by EDM wire cutting and the functional surfaces were made with face milling (SECO tool JHF 980 Special, f z =0.05 mm, v c =200 m/min, ap=0.2 mm), see Fig. 3. Testing was accomplished by special in-situ tensile stage MT1000 made by NewTec (10 kN, a tensile stage). The analysis was carried out in the SEM TESCAN MIRA 3, equipped with the NewTec SoftStrain software - see Fig. 3.

Fig. 3. In-situ tensile testing: a) specimen; b) SECO tool JHF 980, the chip-cross section; c) tensile stage MT1000; d) SEM TESCAN MIRA 3.

3.1. In-situ tensile loading of 7475-T7351

The aim of the in-situ tensile loading was to study mechanism of the crack nucleation and propagation in the 7475-T7351 alloy. Two observations were performed: a) macroscopic observations, embracing the functional area of the whole specimen, and b) microscopic observations, focused on the intermetallic particles in the surface, see Fig.4. Strain distribution was analysed using DIC (Digital Image Correlation). DIC analysis was used to display engineering strain in the selected intermetallic particles under tensile loading, see Fig. 5.

Fig. 4. Microscopic observations of particle cracking: a) intermetallic particle before tensile loading; b) intermetallic particle at yield strength (415-419 MPa); c) intermetallic particle at tensile strength limit (484 MPa).