Local displacements and load transfer in shape memory alloy composites

Abstract

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/poiymer adhesion. Most $MA 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 interracial bond was about 7 percent larger than the value measured experimentally for the sandblasted wire.

Transformation of Embedded Shape Memory Alloy Ribbons

“…The 1 mm debonded length between the SMA ribbon and the epoxy matrix at the edge of the sample is simulated by defining contact surfaces with Coulomb friction coefficient of µ = 0.5, obtained from SMA fiber-epoxy matrix pull-out experiments (Jonnalagadda, Kline and Sottos, 1997). A large value for the gap conductivity between the contact surfaces is chosen such that it ensures a zero temperature jump across the debonded area.…”

“…Recent investigations by Kline, Jonnalagadda and Sottos (1995) and Jonnalgadda, Kline and Sottos (1997) utilized photoelasticity to investigate the interaction between embedded SMA wires and a polymer matrix. The maximum shear stress induced in the matrix due to actuation of the SMA was correlated with the interfacial bond strength of the SMA/polymer interface.…”

Applications of SMA Bundles in Practical Concrete Structures

“…Due to these properties, SMA is usually used to generate bending (Chaudhry & Rogers, 1991;Lagoudas & Tadjbakhsh, 1992), control bucking and postbucking (Baz & Tampa, 1989;Choi et al, 1999Choi et al, , 2000, induce or depress vibration (Baz, Imam, & Mccoy, 1990;Anders, Rogers & Fuller, 1990;Baz, Poh, & Gilheany, 1995;Lau, Zhou, & Tao, 2002), isolate seism (Graesser & Cozzarelli, 1991). Jonnalagadda, Kline, & Sottos (1997) investigated the interaction between SMA wires and a host polymer matrix by correlating local displacements and stress fields induced by the embedded wires with SMA/polymer adhesion, interfacial bond strength was measured for four different SMA surface treatments: untreated, acid etched, hand sanded and sandblasted. Song, Kelly, & Agrawal (2000) presented the design and experimental results of the active position control of a SMA wire actuated composite beam, which has a honeycomb structure with SMA wire embedded in one of its face sheets, a robust controller was designed and implemented to actively control the tip position of the composite beam.…”

Nanostructured Shape Memory Alloys: Composite Materials with Shape Memory Alloy Constituents

“…The interface must have sufficient strength to transfer the stresses and strains from the SMA constituents to the surrounding matrix material, making the investigation of the factors affecting adhesion an important endeavor. Prior studies have investigated surface modification techniques such as sanding, sand blasting, etching, and sleeve-coupling [23][24]. However, these techniques become impractical as particle size decreases.…”