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Proceedings Paper

Thermomechanical representation of the multiaxial behavior of shape memory alloys
Author(s): Dirk Helm; Peter Haupt
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Paper Abstract

A thermomechanically consistent material model representing the multiaxial behavior of shape memory alloys is proposed in this article. The constitutive equations describe the one-way and two-way shape memory effect as well as pseudoelasticity, pseudoplasticity and the transition range between pseudoelasticity and pseudoplasticity. The material model is based on a free energy function as well as evolution equations for internal variables. In detail, the free energy function is introduced in order to describe the energy storage during thermoelastic processes, the energy difference between the regarded phases (austenite and martensite) as well as the energy storage due to the evolution of the residual stresses. In contrast to this, the evolution equations for the internal variables represent the observed inelastic behavior of shape memory alloys as well as the related thermomechanical coupling effects. Due to the description of the energy storage and release during the martensitic phase transitions by means of a mixture theory, one internal variable is the fraction of martensite. Others are the inelastic strain tensor and internal variables describing residual stresses. The viscous material behavior of NiTi shape memory alloys, which is experimentally observed, is represented by an inelastic multiplier of Perzyna-type. Numerical solutions of the developed constitutive equations for isothermal and non-isothermal strain and stress processes demonstrate that the material model represents the main effects of shape memory alloys. Additionally, the material model is able to depict the multiaxial material behavior as observed. Numerical solutions are compared with uniaxial and in particular biaxial experimental observations on NiTi shape memory alloys.

Paper Details

Date Published: 11 July 2002
PDF: 12 pages
Proc. SPIE 4699, Smart Structures and Materials 2002: Active Materials: Behavior and Mechanics, (11 July 2002); doi: 10.1117/12.474992
Show Author Affiliations
Dirk Helm, Univ. of Kassel (Germany)
Peter Haupt, Univ. of Kassel (Germany)

Published in SPIE Proceedings Vol. 4699:
Smart Structures and Materials 2002: Active Materials: Behavior and Mechanics
Christopher S. Lynch, Editor(s)

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