PSI - Issue 35

Andreas Seupel et al. / Procedia Structural Integrity 35 (2022) 10–17 A. Seupel et al. / Procedia Structural Integrity 00 (2021) 000–000

16

7

1 . 2

1

1 . 8

1

˙ t =

| ˙ t | =

4 · 10 − 4 s -1 1 · 10 − 2 s -1 1 · 10 − 1 s -1 1 s -1

martensite volume fraction z 0 . 3 0 . 6 0 . 9 1 . 2 1 . 5 σ true stress | σ | in GPa

martensite volume fraction z

4 · 10 − 4 s -1 1 · 10 − 1 s -1 1 s -1

0 . 8

0 . 8

0 . 9

0 . 6

0 . 6

0 . 3 true stress σ in GPa 0 . 6

σ

0 . 4

0 . 4

z

z

0 . 2

0 . 2

0

0

0

0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0

0

0 . 1

0 . 2

0 . 3

0 . 4

0

true strain

true strain | |

Fig. 4. Simulated predictions and experimental results of stress-strain-curves and martensite evolutions at di ff erent technical strain rates ˙ t : (a) tensile loading and (b) compressive loading. Experiments–dotted lines and symbols, simulations–solid lines. Experimental data from Wolf (2012); Wolf et al. (2014).

50

100

20 | ˙ t | = temperature increase ∆ ϑ in K 40 60 80

10 ˙ t = temperature increase ∆ ϑ in K 20 30 40

1 · 10 − 1 s -1 1 s -1

1 · 10 − 1 s -1 1 s -1

0

0

0 . 3

0 . 4

0 . 3

0 . 4

0

0 . 1

0 . 2

0

0 . 1

0 . 2

technical strain t

technical strain | t |

Fig. 5. Temperature evolution at di ff erent technical strain rates ˙ t for (a) tensile test measured at thermocouple TC 2 and (b) compression test measured at thermocouple TC 3. Experimental data from Wolf (2012); Wolf et al. (2014).

modeling approach, the same experiments need to be performed at di ff erent environmental temperatures. For example, at higher temperatures mechanical twinning becomes dominant, see Rafaja et al. (2020). Yang et al. (2017) observed a negative strain rate sensitivity for TWIP-steels in cases where dynamic strain aging is simultaneously present. This behavior cannot be reflected by the present model. On the other hand, Yang et al. (2017) reported a slight curve crossing or positive strain rate sensitivity for TWIP-steels with other chemical compositions which can possibly be captured.

5. Conclusions

The proposed thermomechanically coupled viscoplasticity model is successfully calibrated at quasi-static loading conditions for di ff erent temperatures. Asymmetry in strain hardening of TRIP-steels is reasonably covered by the Lode-angle dependent evolution of the hardening variable. At higher strain rates, fully thermomechanically coupled FE-simulations of the whole test setups are applied to include a realistic interaction between dissipation, temperature increase, martensite evolution and strain hardening. The model is able to predict the curve-crossing-e ff ect in strain hardening curves in both uni-axial tension and compression. Full dissipation of the inelastic stress power is assumed within the simulations which yields good predictions of temperature rise at local spots for various strain rates.