  Shape Memory Alloys (SMAs) are a unique class of intermetallic alloys that
can cyclically sustain large deformations and recover a designed geometry
through a solid-to-solid phase transformation. SMAs provide favorable actuation
energy density properties, making them suitable for engineering applications
requiring a significant, repeated, work output. To facilitate the development
and validation of an SMA constitutive model considering the evolving
anisotropic material response for High-Temperature SMA (HTSMA), uniaxial and
pure bending actuation cycling tests on HTSMA specimens are performed by a
custom-built testing frames. The phase transformation characteristics for
Ni$_{50.3}$TiHf$_{20}$ HTSMA under uniaxial tension/compression and four-point
bending actuation cycles are investigated. The experimental results show that
the polycrystalline HTSMAs has a strong tension-compression asymmetry under
uniaxial actuation cycling loading conditions. Furthermore, the four-point beam
bending test shows that there is an intrinsic phenomenon when HTSMAs are
subjected to cyclic actuation bending conditions, i.e., the zero-strain neutral
axis shifts as a result of the asymmetric tension-compression phase
transformations and the asymmetric generation of TRIP strains on different
sides of the beam. The conducted experiments provide invaluable information to
develop and improve the SMA constitutive model considering tension-compression
asymmetry and TRIP strain generation within a unified modeling effort. As
future work, additional experiments on other HTSMA components, such as torque
tubes and specimens with notches or cutouts, under actuation cycling would
provide more comprehensive validation data and component performance for
HTSMA-based actuators.
