A Phenomenological Model for Superelastic NiTi Wires Based on Plasticity With Focus on Strain-Rate Dependency Caused by Temperature

[+] Author and Article Information
Ina Schmidt

Helmut-Schmidt-University, University of the Federal Armed Forces Hamburg, Institute of Mechanics, Holstenhofweg 85, D-22043 Hamburg, Germanyina.schmidt@hsu-hh.de

J. Eng. Mater. Technol 128(3), 279-284 (Mar 03, 2006) (6 pages) doi:10.1115/1.2204940 History: Received September 01, 2005; Revised March 03, 2006

A simple one-dimensional model has been developed to illustrate methods to account for transformation bands in plasticity-based models. Austenite-martensite and martensite-austenite transformations are described by two transformation surfaces in analogy to yield surfaces in plasticity theory. The strain-rate dependence of the material behavior is caused solely by the latent heat of the transformations. Optical and thermographical experiments have been carried out to clarify the dependence of the transformation bands on the distribution of latent heat and therefore on the thermomechanical behavior.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Stress-strain curves of superelastic NiTi wires with a diameter 0.9mm under tension at various strain-rates

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Figure 2

Microscopic images of the same location in polycrystalline NiTi specimen at different overall strain levels during loading at a strain-rate of 0.0001s−1

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Figure 3

Thermographic images of a superelastic NiTi specimen in tension test at a strain-rate of 0.01s−1 (pictures with time interval of 0.2s)

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Figure 4

Temperature profiles showing the initial development of latent heat over the length of the specimen

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Figure 5

Modified Prandtl model with friction coefficients dependent on direction of loading and limits for the plastic flow

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Figure 6

Quasi-static simulations at different temperatures

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Figure 7

Simulations with variation of the strain-rate

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Figure 8

Stress and temperature over time at a medium strain-rate (0.25s−1)

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Figure 9

Recalculation of a tensile test at a strain-rate of 0.0002s−1

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Figure 10

Recalculation of a tension test at a strain-rate of 0.002s−1

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Figure 11

Recalculation of a tension test at a strain-rate of 0.0002s−1 with an enhanced model

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Figure 12

Recalculation of a tension test at a strain-rate of 0.002s−1 with an enhanced model

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Figure 13

Areas of hysteresis for tension tests up to 8% strain at different strain-rates



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