Experimental and Numerical Investigation of the Electromechanical Behavior of High Temperature Superconducting Tapes and Cables Subjected to Various Mechanical Loads
Allen, Nathaniel.
2016
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Abstract: Second
generation high temperature superconducting (HTS) tapes have great mechanical properties
as well as excellent high current and high field capabilities. These characteristics
make them a very promising conductor for applications like accelerator and fusion
magnets. Several HTS tape cabling methods are under development for these magnet
applications. To improve fabrication ... read moremethods and maximize operational performance of
these cables composed of several HTS tapes, it is necessary to characterize both the
electromechanical behavior of the full scale cables and of the individual tapes under
anticipated thermal, mechanical and electromagnetic loads. In this work, laboratory
experimentation and structural finite element analysis have been used to investigate the
electromechanical behavior of single HTS tapes and cables. Experiments were conducted to
evaluate critical current performance, the maximum current a superconductor can carry
before becoming resistive, under various loads while finite element analysis was used to
analyze the strain dependence of that critical current for each load type. Single tape
experiments were conducted on three types of commercially available HTS tapes under pure
torsion, axial tension, combined tension-torsion and transverse compression on their
wide face and thin edge. The results from the tests indicate single HTS: under pure
torsion had no reduction in critical current down to a twist pitch of 120 mm; under
axial tension experienced a sharp irreversible critical current degradation at their
yield strength; under combined tension-torsion behaved similar to pure tension samples
for twist pitch lengths greater than 150 mm; and under transverse compression were far
more sensitive to loads applied on their thin edge compared to their wide face. The
single HTS tapes were also analyzed under the same loading conditions using structural
finite element analysis. A novel technique was developed for modeling the layered
composite structure of the HTS tapes using structural solid-shell elements. The
numerical model was able to closely replicate the experimental stress-strain curves and
torque behavior of each type of tape. The simulations also produced detailed axial
strain results which were successfully paired with an analytical model to predict the
critical current performance of the tapes. The numerically predicted critical current
was found to have close agreement with the experimental results for each load type. In
addition to the single tape work, electromechanical experiments on two HTS cabling
methods, designed for high field magnet applications, were conducted. The HTS
cable-in-conduit conductor (CICC) was tested under bending down to a diameter of 0.25 m
and revealed that the minimum safe bending diameter to avoid critical current
degradation was 0.5 m. The twisted stacked-tape cable (TSTC) was tested under mechanical
transverse compression and overall performed better than expected based on real
electromagnetic load degradations seen during high field tests. Both HTS cabling methods
were also analyzed using finite element analysis. A methodology for modeling full scale
three-dimensional HTS cables was developed incorporating contact pair relationships for
modeling the relative motion between tapes. The full scale cables were simulated under
bending and electromagnetic transverse compression. Their numerical strain results were
validated against analytical models and were used to predict the critical current
performance of the cable as done for single tape. The HTS CICC model under bending
agreed well with the experimental critical current results for a nearly frictionless
case having a coefficient of only 0.02, indicating the tapes can slide freely during
bending. The TSTC model under transverse compression found that a solid cylindrical
copper core provides the best support for the tapes under electromagnetic loads. The
overall agreement seen between the experimental measurements and the finite element
analysis validates the electromechanical characteristics of the tapes and cables
presented in this work. Together the numerical and experimental results provided new
details about the strain dependence of the critical current for each load
type.
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Luisa Chiesa.
Committee: Makoto Takayasu, Gary Leisk, Michael Zimmerman, and Thomas Vandervelde.
Keywords: Mechanical engineering, and Canadian history.read less - ID:
- fx719z69f
- Component ID:
- tufts:21170
- To Cite:
- TARC Citation Guide EndNote
