Local displacements and load transfer in shape memory alloy composites |
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Authors: | K Jonnalagadda G E Kline N R Sottos |
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Institution: | (1) Department of Theoretical and Applied Mechanics, University of Illinois at Urbana-Champaign, 61801 Urbana, IL |
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Abstract: | Although there has been a significant amount of research dedicated to characterizing and modeling the response of shape memory
alloys (SMAs) alone, little experimental work has been done to understand the behavior of SMAs embedded in a host material.
The interaction between SMA wires and a host polymer matrix was investigated by correlating local displacements and stress
fields induced by the embedded wires with SMA/polymer adhesion. Most SMA composite applications require transfer of strain
from the wire to the matrix. In these applications, maximum interfacial adhesion between the SMA wire and the polymer matrix
is most desirable. The adhesion was varied by considering four different surface treatments: untreated, acid etched, hand
sanded and sandblasted. The average interfacial bond strength of the SMA wires embedded in an epoxy matrix was measured by
standard pull out tests. Sandblasting significantly increased the bond strength, whereas hand sanding and acid cleaning actually
reduced interface strength. In situ displacements of embedded, surface-treated SMA wires were measured using heterodyne interferometry,
whereas the resulting stresses induced in the polymer matrix were investigated using photoelasticity. Increased wire adhesion
resulted in lower axial wire displacement and higher interfacial stresses due to the restraining effect of the matrix on the
actuated wire. A simplified theoretical analysis was carried out to estimate the shear stress induced in the matrix due to
wire actuation. The maximum shear stress predicted for the case of a perfect interfacial bond was about 7 percent larger than
the value measured experimentally for the sand-blasted wire. |
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