Recently, adaptive wireless devices have utilized displacement of EGaIn within microchannels as an electrical switching mechanism to enable reconfigurable electronics. Device reconfiguration using EGaIn in microchannels overcomes many challenges encountered by more traditional reconfiguration mechanisms such as diodes and microelectromechanical systems (MEMS). Reconfiguration using EGaIn is severely limited by undesired permanent shorting due to retention of the liquid in microchannels caused by wetting and rapid oxide skin formation. Here, we investigate the conditions which prevent repeatable electrical switching using EGaIn in microchannels. Initial contact angle tests of EGaIn on epoxy surfaces demonstrate the wettability of EGaIn on flat surfaces. SEM cross-sections of microchannels reveal adhesion of EGaIn residue to channel walls. Micro-computed tomography (microCT) scans of provide volumetric measurements of EGaIn remaining inside channels after flow cycling. Non-wetting coatings are proposed as materials based strategy to overcome these issues in future work.
We report the first measurements of self-healing polymers with embedded shape memory alloy (SMA) wires.
Improvements of healed peak loads by up to a factor of two are observed, approaching the performance of the
virgin material. Moreover, the repairs can be effected with reduced amounts of healing agent. The improvements
in performance of self-healing polymers with SMA wires are due to three effects: i) crack closure, which reduces
the crack volume, ii) heating of the curing agent during polymerisation, which improves the cross-linking, and
iii) mechanical registration of the two crack faces, which results in a reduced crack volume on closure.
KEYWORDS: Shape memory alloys, Photoelasticity, Composites, Polymers, Finite element methods, Epoxies, Temperature metrology, Data modeling, Fringe analysis, Vibration control
Shape memory alloy (SMA) wires can be embedded in a host material to alter the stiffness or modal response and provide vibration control. The interaction between the embedded SMA and the host material is critical to applications requiring transfer of loads or strain from the wire to the host. Although there has been a significant amount of research dedicated to characterizing and modeling the response of SMA alone, little research has focused on the transformation behavior of embedded SMAs. Photoelastic experiments with SMA wires in polymer matrices had previously provided a qualitative understanding of stress transfer in SMA composites. In the current work, 2D photoelasticity is utilized to quantify the internal stresses induced by the actuation of a thin SMA ribbon in a pure polymer matrix. Through the use of a CCD camera and a frame grabber, photoelastic images are digitally recorded at discrete time increments. Shear stresses induced during the actuation are calculated as a function of time. Computational predictions of shear stress are made using finite element analysis and compared with experimental observations.
Shape memory alloy (SMA) wires can be embedded in a host material to alter the stiffness or modal response and provide vibration control. The interaction between the embedded SMA and the host material is critical to applications requiring transfer of loads or strain from the wire to the host. Although there has been a significant amount of research dedicated to characterizing and modeling the response of SMA alone, little research has focused on the transformation behavior of embedded SMA wires. In the current work, photoelasticity is utilized to quantify the development of internal stresses induced by the actuation of a SMA wire embedded in a pure polymer matrix. Through the use of a CCD camera and a frame grabber, photoelastic images are digitally recorded at discrete time increments. Shear stresses induced during the actuation are calculated as a function of time. Computational predictions of the transformation fronts are made using finite elements analysis and compared with experimental observations.
Interfacial bond strengths of shape memory alloy wires embedded in a polymer matrix and subject to various surface treatments were estimated using pullout tests. Bond strength data was compared to in-situ wire displacements obtained using heterodyne interferometry. Experimental data shows that sandblasting of wires increases the bond strength while handsanding and acid cleaning actually decrease the bond strength. Plasma coating the wires did not significantly alter the adhesion strength. Comparisons with displacement data show that an increase in bond strength results in a decrease in displacement of the wire.
An improved micromechanical model has been developed to predict the hydrostatic response of 1 - 3 piezocomposites. The influence of matrix stiffness, interlayer stiffness, rod aspect ratio, and rod volume fraction on the load transfer and the effective hydrostatic piezoelectric voltage coefficient was investigated. Model predictions treat the ceramic rods as transversely isotropic and relax plane strain assumptions by integrating over the non-uniform strains in the rod and matrix. Results of the current model are compared with predictions from a plane strain model. Optimal interlayer and matrix properties for maximum sensitivity are discussed.
An investigation was made into the feasibility of developing a smart polymer matrix composite which has the ability to self-repair internal microcracks due to thermo-mechanical loading. The investigation focuses on the controlled cracking of hollow repair fibers dispersed in a composite and the subsequent timed release of chemicals which results in the sealing of matrix microcracks and the rebonding of damaged interfaces. In this preliminary work, the mechanisms of chemical release from a single repair fiber embedded in a polymer matrix were investigated using experimental analyses. It was found that controlled cracking of the repair fiber and subsequent release of the repair chemicals could be achieved by applying a polymer coating to the surface of the repair fibers. Release of chemicals into cracks was observed using optical microscopy and photoelasticity. Fiber pull-out and impact tests were performed to examine the ability to rebond fibers and fill cracks, respectively.
The influence of interphase and matrix stiffness on the sensitivity of 1 - 3 piezocomposites is investigated. An analytical model is first developed to predict the static out-of-plane displacements of a single piezoelectric rod composite. The model accounts for the transversely isotropic nature of the ceramic rod and the presence of an interphase region with different properties from the surrounding matrix. Laser interferometry was then utilized to measure displacement profiles for samples consisting of a single PZT-5H rod embedded in Spurr epoxy. Three different interphase conditions were considered. Both the experimental measurements and theoretical predictions demonstrated that changes in the interphase modulus had a significant effect on the maximum displacement on the rod. Rod displacement and sensitivity decreased with increasing interphase stiffness.
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