<p class="MsoNormal" style="margin-bottom: 0in; text-align: justify; line-height: normal">Soft piezoelectric composites (SPCs) show great promise as next-generation energy harvesting materials, with the potential to outperform piezoelectric polymers with limited elastic stretchability (e.g., PVDF) and traditional brittle ceramics (e.g., PZT).&nbsp; Presently, however, SPCs remain an emerging class of materials, with relatively few comprehensive investigations holistically exploring their synthesis, electro-mechanical property characterization, large-strain constitutive modeling, and non-linear dynamics.&nbsp; In this paper, we take first steps toward addressing this compelling research opportunity.&nbsp; A three-component SPC was synthesized, consisting of an ultra-stretchable EcoFlex silicone rubber matrix, micron-sized PMN-PT piezoelectric filler particles, and CNTs that serve as inter-particle conductive “bridges.”&nbsp; Pre-mixed PMN-PT/CNT was stirred with pre-mixed EcoFlex 00-50, degassed in a vacuum oven, cast into custom molds, cured at room temperature for 24 hours, then post-cured at 80 °C for two hours and 100 °C for one hour. &nbsp;The multi-physics properties of the as-cured material were then characterized.&nbsp; Mechanical properties (e.g., small-strain Young’s modulus, UTS, elongation at fracture, and limiting stretch) were quantified through quasi-static uniaxial tension testing.&nbsp; Electrical properties (e.g., dielectric constant and dielectric loss) were obtained using a digital multimeter and parallel-plate capacitor theory.&nbsp; Coupled electro-mechanical properties (e.g., piezoelectric coefficient) were measured using a d33 piezometer. &nbsp;Proper poling was essential for electromechanical coupling. &nbsp;Poling samples at 100 °C for 16 hours in silicone oil produced stable measurements with good repeatability.&nbsp; A thermodynamically consistent, fully nonlinear, finite-strain constitutive model was systematically developed from the ground-up.&nbsp; Deformation, electric field, and initial particle orientation were chosen as the independent variables.&nbsp; A prototype free energy function that contains mechanical, electrical, and piezoelectric contributions was proposed.&nbsp; The mechanical contribution was modeled using Gent hyper-elasticity, which captures strain stiffening at large stretches.&nbsp; Electrical effects were modeled using the ideal dielectric assumption, which jettisons deformation-dependent electrostrictive effects.&nbsp; Piezoelectric coupling was introduced through inclusion of the particle orientation vector, which leads to two-way coupling between mechanics and electricity not present in the isotropic constitutive theory of nonlinear electro-elasticity.&nbsp; The large-stretch non-linear dynamics of a thin, square, soft piezoelectric composite membrane were then investigated.&nbsp; The static stretch of the membrane was numerically determined for a wide range of loads under open- and closed-circuit conditions.&nbsp; Snap-through instabilities were investigated.&nbsp; Excited by sinusoidal fluctuations of the in-plane equi-biaxial tensile load applied on its perimeter, the SPC membrane generated periodic voltage fluctuations.&nbsp; Primary and secondary resonances were identified, and large-amplitude nonlinear dynamic responses near these resonances were investigated about both low-stretch and high-stretch equilibria.</p>

Soft Piezoelectric Composites: Synthesis, Electro-Elastic Property Characterization, and Non-Linear Constitutive Modeling

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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