Page 10 - ASME SMASIS 2016 Program

Symposia

Aizenberg at Harvard University. Dr. He received her PhD in Chemistry constitutive behavior of the SMA is required. A new discovery in the cyclic
from University of Cambridge, Melville Laboratory for Polymer Synthesis, behavior of SMA cables will be shown, where strain ratcheting (cyclic
Cavendish Laboratory and Nanoscience Center. Dr. He’s research focuses shakedown) is sensitive not only to the nominal temperature and stress
biologically inspired dynamic materials, mechanics of responsive soft values but on the order of segments performed in a given thermo-me-
materials, chemical and biological sensors and actuators, with broad chanical loop. As will be shown, this sensitivity stems from the uniaxial
applications in materials science, biomedicine, environment, and energy. tension behavior of
Dr. He is the recipient of the NSF CAREER award, AFOSR Young Investiga-
tor Program award, Harvard Postdoctoral Award for Professional Develop- straight SMA wire, although it does not seem to be well known. Further-
ment, Gates Cambridge Scholarship, UK Overseas Research Scholarship, more, since SMA actuator performance is intimately dependent on heat
the Government Award for National Outstanding Students, and UK transfer between the SMA and the ambient medium, heat transfer
National Excellent Young Scientist Award. Her research on bioinspired measurements of springs in a wind tunnel will be presented, which show
homeostatic materials and novel nanostructured polymeric solar cells for the first time an interesting dependence on angle of attack to the flow
have garnered a number of regional and international awards and was and stretch ratio (pitch) of the spring.
featured in >100 international news outlets.

Biography
THE SHAPE MEMORY BEHAVIOR OF NITINOL CABLES AND John A. Shaw is a professor of aerospace engineering at the University of
SPRINGS Michigan, Ann Arbor, MI, and is the director of the Adaptive Materials and
Structures Laboratory. His research over 20 years spans the fields of
experimental mechanics, thermodynamics, phase transitions, buckling,
John A. Shaw and multi-physics constitutive behavior of materials. Material systems of
University of Michigan interest include shape memory alloys (SMAs), shape memory polymers,
Ann Arbor, MI elastomers, hydrogels, and biological heart muscle. He has a particularly
long-standing interest in the thermo-mechanical behavior of SMAs, the
development and characterization of new structural forms of SMAs, and
their use in novel adaptive structures (including eight patents). He is a
Abstract thrust leader in the General Motors/UM Collaborative Research Laboratory
Nickel Titanium shape memory alloys (SMAs) in wire form have been in Smart Materials and Structures. Honors and awards include an NSF
widely studied and are now being produced in good quality and large CAREER grant, ONR young investigator grant, ASEE Beer/Johnston
volumes at reasonable cost. Other forms are available but are either Outstanding New Mechanics Educator Award, and the best paper award
extremely expensive and/or have poorer shape memory and superelastic- in the International Journal of Solids and Structures in 2013.
ity properties. New experiments are presented on two structural forms,
cables and springs, both of which are made of helical SMA wires.
SYNTHESIS AND CHARACTERIZATION OF FERROMAGNETIC THIN
SMA cable and springs leverage the benefits of SMA wires, yet provide FILMS FOR STRAIN-MEDIATED MULTIFERROIC COMPOSITES
opportunities to tailor and enhance the structural performance in different
ways. SMA cable is a hierarchical architecture where several wires are
wound around a central wire to create a strand, and if desired, several Daniel B. Gopman
strands are then wound around a central strand. Much like conventional Materials Science and Engineering Division,
structural cables, this provides a convenient packaging scheme to scale NIST
up the effective cross-section to withstand large tensile forces, yet the Gaithersburg, MD
SMA endows it with adaptive behavior via the shape memory effect and
superelasticity. The wrap angles can be shallow to give a behavior much
like numerous SMA wires acting in parallel or can be adjusted during Abstract
fabrication to trade force for enhanced displacement. In the extreme case, The high energy required to reverse the magnetization of ultrathin films
a single wire wrapped into a fully coiled helix is an SMA spring, which is presents a challenge to the development of energy-efficient data storage
capable of extremely large elongations at low tension. and spintronics applications. The non-volatility required in magnetic
nano-objects for high-density storage and logic requires high anisotropy
The known behavior of SMA cables and springs will be reviewed, and new thin film materials such that the ratio of anisotropy energy to thermal
thermomechanical experiments will be shown that explore their use in an energy (KV/kBT) is greater than 50, where K is the anisotropy energy
actuator mode. The range of actuation forces between various cable density, V is the volume of a single magnetic nano-object, kB is the
constructions and springs is immense, ranging from a few to tens of Boltzmann constant and T is the temperature. At the same time, the
thousands of newtons, providing a large space for the design of uniaxial energy consumed by switching the magnetization (10’s of fJ according to a
SMA actuators to suit user needs. At the component scale, helical wires recent industry statement) should be minimized in order to realize energy
experience a combination of tension, bending, and torsion to varying efficient magnetic random access memory (MRAM) devices. One way to
10
degrees, depending on the wrap angle. Challenges for future modeling reduce the energy required for reversing the magnetization while
efforts will be discussed, since a good knowledge of the multiaxial maintaining sufficient magnetic anisotropy energy for thermal stability is to