PSI - Issue 2_A

Ezio Cadoni et al. / Procedia Structural Integrity 2 (2016) 986–993

992

Author name / Structural Integrity Procedia 00 (2016) 000–000

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a)

b) Fig. 7. (a) True stress versus true strain at di ff erent strain rates; (b) Photo of the specimen after a high strain rate test.

Fig. 8. Comparison between the experimental results and the predictions of Johnson?Cook material model for the true stress versus true plastic strain curves of AA7081 at di ff erent strain rates.

the experimental data. A is the true yield stress of the material at the strain rate of 0 . 001 s − 1 . The material parameters B and n represent the strain hardening e ff ects of the material at the strain rate 0 . 001 s − 1 . The strain rate sensitivity parameter is represented by the C parameter. The temperature e ff ects are not taken into account in this case. On substituting the Johnson-Cook model parameters in the eqn. (4), the concrete equation of this model is obtained for AA7081 as eqn. (5). σ JC = 533 + 613 · 0 . 7071 p · 1 + 0 . 0378 · ln (˙ ∗ ) (5) The comparisons between the predictions from Johnson-Cook model and experimental results at low and high strain rates are shown in Fig.8.