Issue |
ESOMAT 2009
2009
|
|
---|---|---|
Article Number | 03009 | |
Number of page(s) | 9 | |
Section | Principles, Simulations, Materials: Mathematical Modelling | |
DOI | https://doi.org/10.1051/esomat/200903009 | |
Published online | 01 September 2009 |
DOI: 10.1051/esomat/200903009
Effect of plastic slip on thermomechanical behavior of NiTi polycrystals investigated by micromechanics modelling
V. Novák1, P. Šittner1, J. Pilch1 and R. Delville21 Institute of Physics ASCR, Na Slovance 2, Prague, Czech Republic
2 EMAT, University of Antwerps, Belgium
novakv@fzu.cz
Published online: 1 September 2009
Abstract
Earlier developed micromechanics crystallographic model of SMA polycrystals has
been modified by incorporating plastic deformation as additional deformation mechanism.
It is assumed that dislocation slip proceeds in austenite and B19‘ martensite phases
in parallel with the processes derived from B2B19‘martensitic transformation in NiTi alloy.
The model was used to simulate the responses of NiTi polycrystal in three thermomechanical
cycles typically carried out in the SMA research. Based on the simulation results, it is
proposed that, due to the dislocation slip occurring simultaneously with transformation
related processes, the stresses and strains in the transforming polycrystal are
significantly redistributed which in turn modifies the macroscopic thermomechanical
responses. In tensile tests at low temperature, the plastic deformation occurs in
martensite phase after the stress induced transformation or martensite reorientation,
while at medium and high temperatures both deformation mechanisms proceed in parallel.
Depending on whether the plastic deformation in tensile tests had taken place in the
austenite (typically at high temperatures) or in the martensite (typically at low temperatures)
phase, distribution of internal stresses is quite different. Surprisingly, significant plastic
deformation activity is predicted for the cooling/heating tests under constant tensile stress.
Plastic deformation occurs in this case mainly in the martensite state and redistribution of
stress plays significant role. Results of the simulation of the cyclic tensile test at
constant temperature explain qualitatively most of the features of the unstable
superelastic stress-strain curves observed in cyclic loading experiments. It is
proposed that the actual reason for accumulation of unrecovered strain during cyclic
loading is in fact the continuously evolving distribution of internal stresses, strains and
phase fractions – it causes the plastic deformation to progress even if the macroscopic
maximum strain remains constant and peak stress decreases upon cyclic loading.
Note to the reader:
On pages 03009-p3, 03009-p6, 03009-p7 and 03009-p8 several mistakes have been corrected on October 19, 2009.
© Owned by the authors, published by EDP Sciences 2009