In the current study Active Fiber Composites (AFC) utilizing Lead-Zirconate-Titanate (PZT) fibers with Kapton screen printed interdigitated electrodes (IDE) were integrated into orthotropic glass fiber reinforced plastic (GFRP) laminates to investigate integration issues associated with smart structures and host laminate integrity. To aid in this goal surrogate or "Dummy" AFC (DAFC) were designed using a GFRP core and Kapton outer layers to match the longitudinal mechanical and interface properties of the AFC. 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. Two integration techniques, cutout and simple insertion were investigated using DAFC, with little difference seen between the integrity of laminates prepared using these two methods. Using this testing scheme the influence of device placement in relation to position extending away from the laminate symmetric axis was found to have an effect on laminate integrity in tensile loading. As the DAFC were placed far from the laminate symmetry axis, the ultimate tensile strength and strain of the laminates decreased in a linear manner while the Young's modulus of the laminates remained constant. Similar trends were observed with integrated AFC specimens. The performance of integrated AFC was characterized using monotonic cyclic tensile loading with increasing strain levels. A transition region was observed between strains of 0.05%-0.50%, with a dramatic decrease in AFC sensitivity from a maximum to minimum value.
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.
The morphology and the free strain performances of three different piezoelectric ceramic fibers used for the manufacture of active fiber composites (AFCs) have been investigated. The morphology of the fibers has a direct influence on the manufacture of the AFCs. Fibers with non-uniform diameters are more difficult to contact with the interdigitated electrodes and can be the cause of irreparable damages in AFCs. An indirect method requiring the use of a simple analytical model is proposed to evaluate the free strain of active fiber composites. This indirect method presents a relatively good agreement with direct free strain measurements performed with strain gages glued on both sides of an AFC. The results show a systematic difference of ca. 20 % between the indirect and the direct methods. However, the indirect method did not permit to see differences of piezoelectric performance between the types of fibers.
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