Interactive WWW Page for the Simulation of Shape Memory Alloys
O. Heintze and S. Seelecke
26 June, 2000
Shape memory alloys (SMAs) exhibit a very complex material behavior. Depending on load and temperature a number of unusual effects like shape memory or superelasticity may be observed in these metals. These phenomena are due to a martensite-austenite phase transition in the crystal lattice and to martensitic twinning. The interested reader is refered to the textbooks of Funakubo (1984) and Otsuka and Wayman (1999) for an introduction to the subject. A short overview can also be found here at this web site.
The material behavior of SMAs has inspired a quickly increasing number of technical applications in a diversity of fields, among them biomedicine, energy conversion, structural damping and actuation of smart structures. An overview can be found in the recent review article by Seelecke and Müller (2000) and the numerous references therein.
The design of such applications requires not only good knowledge of the principles of SMA behavior - in order to make quantitative predictions, mathematical models are needed as well. A large number of such models have been developed during the last two decades at different levels of sophistication, and some of them have even been incorporated into finite element codes for realistic structural analyses; see the above review article again for references.
However, most of these models only exist as research codes, preferably written in FORTRAN or C/C++, and they are not readily available to the public. Through the rapid development of the Internet and in particular the World Wide Web (WWW) it has become feasible to bring the subject closer to the user. The basis is JAVA, a programming language developed by Sun Microsystems, which is supported by all major web browsers. This makes a program written in JAVA totally platform independent and accessible from virtually everywhere in the world, provided the user has an Internet access.
The present web page is the result of a final-year project, carried out at the Institute of Thermodynamics, TU Berlin, see Heintze (2000) for details. The objective was to convert the existing code of the SMA model developed by Seelecke, Müller and Achenbach, see Seelecke (1999), from FORTRAN to JAVA. Based on this JAVA code, a graphical user interface (GUI) has been developed that allows the user to define a number of parameters for a deformation controlled tensile/compressive experiment with a SMA specimen. As a result of the simulation, the user can produce a number of diagrams: stress, temperature and phase fractions as functions of time. Also attainable are the hysteretic load-deformation curves, appropriate to different temperatures. All these curves are relevant for the interpretation of typical experiments and are useful for a basic understanding of SMA phenomena.
Currently, it is possible to study the influence of the
- environmental temperature, such that the full range from quasiplasticity to pseudoelasticity may be simulated,
- duration of the experiment such that the effect of the rate of deformation is exhibited,
- extremal values of deformation, so that incomplete hysteresis may be investigated,
- heat exchange coefficient with the environment, so that the effect of different surrounding media can be demonstrated.
The model includes a full thermomechanical coupling to account for all of the above effects. All material data are those of a typical NiTi wire, the most commonly used shape memory alloy.
This web page is a first prototype; so far, at least to the knowledge
of the authors, no other possibility exists to simulate SMA behavior via
the Internet. There is a large number of additional features that could
be implemented, and we should be happy to receive feedback
with requests for extensions.
References
Funakubo H, ed (1984), Shape Memory Alloys, Gordon and Breach Science Publishers
Heintze O (2000), Interactive Webpage for the Simulation of Shape Memory Wires (in German), Studienarbeit, TU Berlin
Otsuka K and Wayman CM, eds (1998), Shape Memory Materials, Cambridge University Press, UK
Seelecke S (1999), Adaptive Structures with SMA Actuators - Modeling and Simulation (in German), Habilitation thesis, TU Berlin
Seelecke S, Müller I (2000), Shape Memory Alloy Actuators in Smart Structures- Modeling and Simulation, ASME Applied Mechanics Reviews, submitted
