The magnetoresistance behavior of the polyurethane composites reinforced with iron nanoparticles which has been heat
treated was reported. The flexible nanocomposites were fabricated by the surface-initiated-polymerization (SIP) method.
The uniformly distributed nanoparticles within the polymer matrix, well characterized by field emission scanning
electron microscopy, favor a continuous carbon matrix formation after annealing, rendering the transition from
insulating to conductive composites. The coercive forces reflect strong particle loading and matrix dependent magnetic
properties. The obtained nanocomposites possess fairly good giant magnetoresistance (MR), with a MR of 7.3 % at room
temperature and 14 % at 130 K. Furthermore, the formed carbon matrix has a 7 wt.% argon adsorption potential for fuel
cell applications.
In this paper we describe the results of an ongoing experimental program to measure the strain distribution around a simulated void in a piezoceramic material subjected to large electric fields. The simulated void is a two- dimensional circular cylinder fabricated into the sample. Strain information is acquired with a Moire interferometric system which permits both quantitative evaluation of surface strains and qualitative information regarding domain reorientation. Results indicate that large stresses/strains arise around the perimeter of the hole prior to domain reorientation. Domain switching initiates at the locations where the largest stress/strain occurs around the perimeter of the simulated void and do so to reduce the localized concentrations. During this evolutionary process the material contains a multi-domain structure with regions polarized in 180 degree(s) apart. Domain switching appears to be predominately 180 degree(s) without any 90 degree(s) domain reorientation occurring at the mesoscopic level. Results suggest that large stress/strain concentrations around voids could be a source for electric fatigue degradation.
In this study an analytic and experimental effort is presented to understand and improve the fracture toughness and the associated fatigue behavior of piezoceramic materials. Analytical models are presented on the premise that defects in the form of voids cause material degradation during electric excitation. A unit cell approach employing an exact linear electroelastic analysis is used to study the stress and electric field concentrations as a function of material properties. Our study indicates that for certain ratios of piezoelectric coefficients electric field induced stress concentrations are eliminated in the material. These results suggest that the electric fatigue life of a piezoelectric ceramic can be extended if the piezoelectric properties are appropriately tailored during the manufacturing processes. However, this analytical work is done within the frame work of linear piezoelectricity. To better understand internal stress concentrations arising due to nonlinear phenomena associated with polarization switching, we present experimental results using moire interferometer. This first application of moire interferometer to piezoceramics demonstrates the promise this experimental technique offers to better understand internal stress/strain distributions. In this initial presentation we present two fundamental results, that is the strain concentrations between domains oriented 180 and 90 degrees apart.
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.