PSI - Issue 2_A

L. Bertini et al. / Procedia Structural Integrity 2 (2016) 681–689 Author name / Structural Integrity Procedia 00 (2016) 000–000

683

3

The stress t  (true) rather was evaluated and considered, rather than the engineering stress  , for a more direct measure of the material’s response in the plastic flow range. Fig. 2 shows the true stress-strain curve, superimposed to the engineering curve, and the related parameters are reported in tab. 2.

Fig. 2. Engineering and True stress-strain curves.

Table 2. Parameters tensile test

f t S (MPa)

f t  (%)

ut t S (MPa)

ut t  (%)

787

1300

12

100

2.2. Cyclic characterization In order to cyclically characterize the material, several deformation (strain) control tests have been performed: 4 load steps have been imposed to gradually bring the material in the plastic range. The values of stresses and strains in the various load steps are listed in Tab. 3

Table 3. Stress and strain values at various steps. Step 1 Step 2 Step 3 Step 4   (%) ± 0.2 ± 0.5 ± 1 ± 2   (MPa) ± 380 ± 500 ± 510 ± 580

Fig. 3. (a) Hysteresis loops measured during the tests and cyclic curve (dashed), (b) comparison between the cyclic curve (dashed) and monotonic tensile curve (green).