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.
Inspired by natural examples of microvascular systems in a wide variety of living organisms, we perform the
computational design of a new class of polymer-based composite materials with the unique ability to heal and/or
cool in a completely autonomic fashion, i.e., without any external intervention. The design process combines
graph theory to represent and evaluate the microvascular network and Genetic Algorithms (GA) to optimize
the diameter of its microchannels. In this work, a multi-objective GA scheme has been adopted to optimize the
network topology against conflicting objectives, which include (i) optimizing the flow properties of the network
(i.e., reducing the flow resistance of the network to a prescribed mass flow rate) and (ii) minimizing the impact
of the network on the stiffness and strength of the resulting composite in terms of the void volume fraction
associated with the presence of the microvascular network. The flow analysis of the network is performed based
on the assumption of fully established Poiseuille flow in all segments of the network, leading to the classical
proportionality relation between the pressure drop along a segment and the mass flow rate. The optimized
structures resulting from the optimization can then be manufactured using an automated process ("robotic
deposition") that involves the extrusion of a fugitive wax to define the network. Once manufactured, the
computer-aided design can then be validated through a comparison with the results obtained from flow tests.
This presentation focuses on the results of the optimization of an epoxy-based composite material containing a
two-dimensional microvascular network.
A new class of materials called smart tagged composites has great potential for use in structural health monitoring. This paper introduces concepts and interrogation schemes for piezoelectric tagged composite materials. Experiments were undertaken to demonstrate the feasibility of piezoelectric tagging by incorporating PZT-5A particles into a polyester matrix. Several types of diametral compression specimens were fabricated and tested to failure while monitoring the induced charge across electrodes placed on the front and back faces of the specimens. The effect of volume fraction of piezo particles and glass reinforcement was investigated along with connectivity of the piezo phase. Small amounts of graphite were added to some specimens to aid in the poling process, however this proved to be of little benefit. The greatest sensitivity and highest induced fields were obtained for a pseudo 1 - 3 piezocomposite system with 6% volume fraction loading of the piezo phase.
Experimental data for 55/45 Ni-Ti alloy (Nitinol) is presented in this work for correlation to phenomenological and thermodynamic/micromechanical constitutive and transformation models for shape memory alloys. Hysteresis data is used to obtain the transformation temperatures Ms-martensitic start, Mf-martensitic finish, As-austenitic start, and Af-austenitic finish. Nitinol wires are mechanically tested in tension at five different temperatures: below Mf, at (Ms + Mf)/2, at (M2 + As)/2, at (As + Af)/2, and above Af. For the phenomenological models, several characterization parameters are required. These are obtained experimentally and the models are correlated with the data.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.