In the current study Active Fiber Composites (AFC) utilizing Lead-Zirconate-Titanate (PZT) fibers with Kapton(R) screen printed interdigitated electrodes (IDE) were integrated into carbon fiber reinforced plastic (CFRP) laminates to investigate integration issues associated with smart structures and host laminate integrity. To aid in this goal surrogate or "dummy" AFC (DAFC) using a composite core and Kapton(R) outer layers (to match the longitudinal mechanical and interface properties of the AFC) were employed. These DAFC were used in place of real AFC to expedite test specimen manufacture and evaluation. This allowed efficient investigation of the impact of an integrated AFC-like inclusion on laminate mechanical integrity. Laminates with integrated AFC were additionally tested with signal monitoring to assess AFC health during the test. Investigation into laminate failure was accomplished via a finite element model of the system which was created in ANSYS to investigate failure in the composite plies. Tsai-Wu failure criterion was calculated to investigate laminate failure characteristics. Integration of AFC into CFRP laminates degraded laminate strength by 13.3% using insertion integration and 7.8% using the interlacing integration technique. The finite element model showed that interlacing integration enabled distribution of critical forces over the entire laminate while insertion integration led to critical forces concentrating over the integration region.
The scientific community has put significant efforts into the
manufacturing of sensors and actuators made of piezoceramic fibers
with interdigitated electrodes. These allow for increased
conformability, integrability in laminate structures and offer
high coupling factors. They are of particular interest for damping
applications. This paper presents a comparison between
piezoceramic monolithic actuators and Active Fiber Composites
(AFCs) for shunt damping. For this purpose, the different
actuators were bonded on aluminum cantilever plates, respectively
embedded in a glass fiber composite cantilever plate. The
vibration suppression was attained by converting the electric
charge by means of the converse piezoelectric effect and
dissipated through robust resonant shunt circuits. A new circuit
topology was used, which enables efficient damping even with low
piezoelectric capacitance. An integrated FE model was implemented
for prediction of the natural frequencies, the optimum values for
the electric components and the resulting damping performance.
Patches working in the direct 3-3 mode show much better specific
damping performance than the 3-1 actuated patch. The comparison
between monolithic and AFC actuators shows that AFCs fulfill
integrability and performance requirements for the planned damping
applications.
The scientific community has put significant efforts in the
manufacturing of sensors and actuators made of piezoceramic fibers
with interdigitated electrodes. These allow for increased
conformability and actuation capability at high field regime. The
prediction of their coupled field behavior, however, is so far
limited to low field applications, where the piezoelectric
coupling coefficient is assumed to be constant. An approach, which
takes into account the strain driven nonlinearity of a
representative work cycle at high field regime is still lacking.
This study presents a nonlinear Finite Element Model to simulate
the free strain properties of Active Fiber Composites (AFCs) under
high electric field conditions. Input data for the fully
parametric model are the Representative Volume Element (RVE)
geometry and the material properties of its piezoceramic and epoxy
resin components. The high field properties of single PZT fibers
under free strain conditions were determined using a novel
characterization procedure. Free strain properties of the
actuators were measured experimentally, and important geometrical
parameters (contact angle between the fiber and the electrode,
average spacing between the fibers) were measured using
micrographical imaging. The results of the simulation show good
agreement with the free strain measurements, allowing for
prediction of a representative work cycle hysteresis. The
influence of important geometrical parameters on the actuator
properties such as electrode spacing and electrode-fiber contact
angle was investigated both numerically and experimentally.
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