With increased usage of shape memory alloys (SMA) for applications in various fields, it is important to understand how the material behavior is affected by factors such as texture, stress state and loading history, especially for complex multiaxial loading states. Using the in-situ neutron diffraction loading facility (SMARTS diffractometer) and ex situ inverse pole figure measurement facility (HIPPO diffractometer) at the Los Alamos Neutron Science Center (LANCE), the macroscopic mechanical behavior and texture evolution of Nickel-Titanium (Nitinol) SMAs under sequential compression in alternating directions were studied. The simplified multivariant model developed at Northwestern University was then used to simulate the macroscopic behavior and the microstructural change of Nitinol under this sequential loading. Pole figures were obtained via post-processing of the multivariant results for volume fraction evolution and compared quantitatively well to the experimental results. The experimental results can also be used to test or verify other SMA constitutive models.
The usage of shape memory materials has extended rapidly to many fields, including medical devices, actuators, composites, structures and MEMS devices. For these various applications, shape memory alloys (SMAs) are available in various forms: bulk, wire, ribbon, thin film, and porous. In this work, the focus is on SMA hybrid composites with adaptive-stiffening or morphing functions. These composites are created by using SMA ribbons or wires embedded in a polymeric based composite panel/beam. Adaptive stiffening or morphing is activated via selective resistance heating or uniform thermal loads. To simulate the thermomechanical behavior of these composites, a SMA model was implemented using ABAQUS' user element interface and finite element simulations of the systems were studied. Several examples are presented which show that the implemented model can be a very useful design and simulation tool for SMA hybrid composites.
A simplified multivariant model for SMA single crystals is developed. Although the new model is a simplified version, removing explicit interaction energy calculations, it considers certain aspects of martensite transformation much better. Most significantly, martensite variants tend to rapidly form large plates most of which have an invariant plane interface with the austenite and/or reach the grain boundary. Hence the formulation of the previous Multivariant model in which every variant group is embedded in the austenite phase together with numerous other inclusions is inaccurate. In the simplified model, the energy contributed by the incompatibility of inclusion to the matrix is neglected. The prediction by the new model for different uniaxial tension directions on a single CuAlNi crystal agrees excellently with the experimental results. Furthermore, the counter-intuitive results for a polycrystalline CuZnAl SMA under triaxial loading are also well captured by the simplified model. Experimental result considering in situ loading in the MTS loading frame and SEM are shown illustrating the invariant plane in a single (gamma) '1 CuAlNi crystal under uniaxial loading. These results also necessitate further microstructure mapping for phase transition and detwinning and/or reorientation of correspondence variants in SMA with an internal twinned structures.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.