CSAR Seminar
SPEAKER: Youngjean Jung, Princeton University
TITLE:
Constitutive Modeling and Numerical Simulation of Multivariant Phase
Transformation in Polycrystalline NiTi Alloys
DATE: Thursday, July 27, 2006
TIME: 2:00 P.M.
PLACE: 2240 DCL
1304 W. Springfield Ave., Urbana, IL
ABSTRACT
Tension-torsion tests are conducted on thin-walled tubes
(thickness/radius ratio of 1:10) of the polycrystalline superelastic
Nitinol using various loading/unloading paths under isothermal
conditions. A micromechanical constitutive model, algorithmic
implementation and numerical simulation of polycrystalline superelastic
alloys under biaxial loading are developed. The constitutive model is
based on the micromechanical structure of Ni-Ti crystals and accounts
for the physical observation of solid-solid phase transformations. The
model is formulated in finite deformations and incorporates the effect
of texture which is of profound significance in the mechanical response
of polycrystalline Nitinol tubes. The numerical implementation is
based on the constrained minimization of a functional corresponding to
the Helmholtz energy with dissipation. Special treatment of
loading/unloading conditions is also developed to distinguish between
forward/reverse transformation state. Simulations are conducted for
thin tubes of Nitinol under tension-torsion, as well as for a
simplified model of a biomedical stent.