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Monday, September 22, 2008: 12:15 PM
Room C (Palazzo dei Congressi di Stresa)
This paper presents a tensorial model capable of describing quantitatively 3D pseudoelastic deformation associated with stress-induced martensitic transformation and ferroelastic deformation associated with martensite reorientation of polycrystalline shape memory alloys (SMAs). The main assumptions of the "elastohysteresis" model include the following. (i) The model does not use concepts of elastoplasticity theory, i.e. no decomposition of the strain rate and no elastic domain limited by plasticity or transformation surfaces. (ii) It is based on the theories of hyperelasticity and hypoplasticity (the behavior is always irreversible) and leads to a thoroughly non-linear relation between the stress and strain rates. (iii) It is built on the basis of a finite number of "memorized" special events (erasable micromemories).
For the deformation of SMAs, the stress is expressed as an additive combination of a hyperelastic part (mainly associated with the reversible martensitic transformation) and a hysteresis part. Tension-compression asymmetry is taken into account. The model is implemented in an academic 3D finite element software Herezh++ and simulations are compared with experimental data for NiTi and Cu-Al-Be SMAs.
The model was validated on experimental results obtained from conventional simple tests, including traction, compression and shear and for full and partial deformation cycles. The validation was made with regard to both the loading and unloading stress-strain paths and the stress hysteresis of the full and partial deformation loops.
Then two series of multiaxial loading conditions including proportional and non-proportional loading were simulated. The former was concerned with axial tension-internal pressure testing of thin-wall tubes and the latter was concerned with biaxial compressive tests of cubical samples, both of a Cu-Al-Be. Rectangular and square loading paths were studied for the non-proportional tests. Finally, a cantilever beam is simulated using Herezh++ for both ferroelastic and pseudoelastic bending deformations.
For the deformation of SMAs, the stress is expressed as an additive combination of a hyperelastic part (mainly associated with the reversible martensitic transformation) and a hysteresis part. Tension-compression asymmetry is taken into account. The model is implemented in an academic 3D finite element software Herezh++ and simulations are compared with experimental data for NiTi and Cu-Al-Be SMAs.
The model was validated on experimental results obtained from conventional simple tests, including traction, compression and shear and for full and partial deformation cycles. The validation was made with regard to both the loading and unloading stress-strain paths and the stress hysteresis of the full and partial deformation loops.
Then two series of multiaxial loading conditions including proportional and non-proportional loading were simulated. The former was concerned with axial tension-internal pressure testing of thin-wall tubes and the latter was concerned with biaxial compressive tests of cubical samples, both of a Cu-Al-Be. Rectangular and square loading paths were studied for the non-proportional tests. Finally, a cantilever beam is simulated using Herezh++ for both ferroelastic and pseudoelastic bending deformations.