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Symposia Invited Speakers
SYMPOSIUM 1 SYMPOSIUM 1
SELECTIVE LASER MELTING OF NITI AND NITIHF SHAPE PIEZORESISTIVE NANOCOMPOSITES FOR STRAIN AND
MEMORY ALLOYS DAMAGE SENSING: EXPERIMENTAL AND COMPUTATIONAL
OBSERVATIONS
Haluk Karaca Gary Seidel
Associate Professor Associate Professor
Department of Mechanical Engineering Kevin T. Crofton Department of Aerospace
University of Kentucky and Ocean Engineering
Virginia Tech
Abstract
Abstract
Shape Memory Alloys (SMAs) exhibit unique functional properties such
as shape memory effect and superelasticity. The traditional fabrication The addition of small amounts of conducting and semi-conducting
methods of SMAs are challenging and not flexible to produce porous and nanomaterials such as carbon nanotubes and graphene to non-
complex structures. An additive manufacturing method of Selective Laser conducting polymers has been observed to yield nanocomposites
Melting (SLM) is an attractive method that employs CAD data to selectively which demonstrate a strong piezoresistive effect, especially near the
melt the metal powder via a laser beam to fabricate complex parts. The percolation concentration. Gauge factors for strain sensing for these
SLM parameters such as laser power, powder layer thickness, scanning nanocomposites can range from values comparable to metallic wire strain
speed, spacing, and strategy can be used to tailor the microstructural gauges to values that are an order of magnitude or more higher, depending
characteristics and thus the shape memory properties of the fabricated on the concentration, dispersion, and orientation distribution of the
part. In this talk, the recent developments, challenges, opportunities, and nanomaterials used. However, the real advantage of these piezoresistive
results on the SLM fabricated NiTi and NiTiHf shape memory alloys will nanocomposites compared to conventional strain gauges is that they can
be presented. readily be embedded within structural members and structural materials,
particularly those that make use of polymer matrix composites. Moreover,
Biography the gauge factors for these nanocomposites have been observed to grow
dramatically as damage initiates and propagates through these composites
Dr. Haluk Karaca is an Associate Professor at the Mechanical Engineering providing embedded damage sensing and, hence, an opportunity for
Department of University of Kentucky. He is a recipient of NSF Career award use in structural health monitoring applications. Further distinguishing
and Associate Editor of the Journal of Intelligent Materials and Systems. piezoresistive nanocomposites from metallic wire strain gauges is their
He received his Ph.D. from Texas A&M University in 2007. He has worked ability to make use of both inherent effective piezoresistivity and geometric
on the characterization and processing of conventional, high temperature piezoresistance, the latter being tied solely to elastic properties where the
and magnetic SMAs, indentation response of SMAs and shape memory former derives from direct changes in resistivity in response to strain. The
composites, and published more than 70 journal articles in this field. mechanisms believed to be driving the inherent effective piezoresistive
response originate chiefly at the nano- and microscales. At the nanoscale,
nanomaterials can exhibit inherent piezoresistivity and electron hopping
or quantum tunneling. At the microscale, the dispersion of nanomaterials
leads to the formation of conductive networks which can increase or
decrease in number of conductive paths in response to applied strain or
damage initiation and propagation. This talk will provide an overview of
both experimental and computational observations of the piezoresistive
response of nanocomposites as applied to both strain and damage
sensing. Nanocomposites will be discussed in the context of the effects
of concentration, dispersion, and orientation distribution. Composites with
embedded sensing will be discussed in the context of applications for
fuzzy fibers in composite laminates and piezoresistive binders in energetic
materials. Lastly, the talk will emphasize the need for and application
of multiscale multiphysics modeling tools for both understanding and
engineering piezoresistive nanocomposites.
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