CLOSED TWO-WAY SHAPE MEMORY EFFECT IN UNIDIRECTIONAL COMPOSITE WITH SHAPE MEMORY ALLOY FIBERS AND ELASTIC MATRIX

Because of being in possession of shape memory effect and superelasticity, Ni-Ti shape memory alloys have earned more intense gaze on the next generation applications. Conventionally, Ni-Ti shape memory alloys are manufactured by hot forming and constraint aging, which need a capital-intensive investment. To have a cost benefit getting rid of plenty of die sets, this study is aimed to form Ni-Ti shape memory alloys at room temperature and to age them at elevated temperature without any die sets. In this study, starting with solution treatments at various temperatures, which served as annealing process, Ni-rich Ni-Ti shape memory alloy wires were bent by V-shaped punches in different curvatures at room temperature. Subsequently, the wires were aged at different temperatures to have shape memory effect. As a result, springback was found after withdrawing the bending punch and further after the aging treatment as well. A higher solution treatment temperature or a smaller bending radius leads to a smaller springback, while a higher aging treatment temperature made a larger springback. This springback may be compensated by bending the wires in further larger curvatures to keep the shape accuracy as designed. To explore the shape memory effect, a reverse bending test was performed. It shows that all bent wires after aging had a shape recovery rate above 96.3% on average.

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The Concept of Physical Metric in the Thermomechanical Modeling of Phase Transformations With Emphasis on Shape Memory Alloy Materials

Journal of Engineering Materials and Technology ◽

10.1115/1.4023780 ◽

2013 ◽

Vol 135 (2) ◽

Cited By ~ 3

Author(s):

Vassilis P. Panoskaltsis ◽

Lazaros C. Polymenakos ◽

Dimitris Soldatos

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Phase Transformations ◽

Shape Memory Effect ◽

Memory Effect ◽

Material Model ◽

Internal Variable ◽

Theoretical Interest ◽

Numerical Examples ◽

Thermomechanical Modeling

In this work we derive a new version of generalized plasticity, suitable to describe phase transformations. In particular, we present a general multi surface formulation of the theory which is capable of describing the multiple and interacting loading mechanisms, which occur during phase transformations. The formulation relies crucially on the consideration of the intrinsic material (“physical”) metric as a primary internal variable and does not invoke any decomposition of the kinematical quantities into elastic and inelastic (transformation induced) parts. The new theory, besides its theoretical interest, is also important for application purposes such as the description and the prediction of the response of shape memory alloy materials. This is shown in the simplest possible setting by the introduction of a material model. The ability of the model in simulating several patterns of the experimentally observed behavior of these materials such as the pseudoelastic phenomenon and the shape memory effect is assessed by representative numerical examples.

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Sensitivity and Uncertainty Analysis of One-Dimensional Tanaka and Liang-Rogers Shape Memory Alloy Constitutive Models

Materials ◽

10.3390/ma12101687 ◽

2019 ◽

Vol 12 (10) ◽

pp. 1687 ◽

Cited By ~ 5

Author(s):

A. B. M. Rezaul Islam ◽

Ernur Karadoğan

Keyword(s):

Shape Memory Alloy ◽

Uncertainty Analysis ◽

Shape Memory ◽

Shape Memory Effect ◽

Memory Effect ◽

Constitutive Models ◽

Loading Conditions ◽

Input Parameters ◽

Stress Dependent ◽

Sensitivity And Uncertainty Analysis

A shape memory alloy (SMA) can remember its original shape and recover from strain due to loading once it is exposed to heat (shape memory effect). SMAs also exhibit elastic response to applied stress above the characteristic temperature at which transformation to austenite is completed (pseudoelasticity or superelasticity). Shape memory effect and pseudoelasticity of SMAs have been addressed by several microscopic thermodynamic and macroscopic phenomenological models using different modeling approaches. The Tanaka and Liang-Rogers models are two of the most widely used macroscopic phenomenological constitutive models for describing SMA behavior. In this paper, we performed sensitivity and uncertainty analysis using Sobol and extended Fourier Amplitude Sensitivity Testing (eFAST) methods for the Tanaka and Liang-Rogers models at different operating temperatures and loading conditions. The stress-dependent and average sensitivity indices have been analyzed and are presented for determining the most influential parameters for these models. The results show that variability is primarily caused by a change in operating temperature and loading conditions. Both models appear to be influenced by the uncertainty in elastic modulus of the material significantly. The analyses presented in this paper aim to provide a better insight for designing applications using SMAs by increasing the understanding of these models’ sensitivity to the input parameters and the cause of output variability due to uncertainty in the same input parameters.

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