Deployable Piezoelectric Thin Shell Structures: Concepts, Characterization and Vibration Control

Citation

Wei, Yuchen (2019) Deployable Piezoelectric Thin Shell Structures: Concepts, Characterization and Vibration Control. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4DRX-2X87. https://resolver.caltech.edu/CaltechTHESIS:06072019-114129662

Abstract

The thesis presents three interconnected technology paths to the design and realization of novel deployable active thin shell structures. The baseline concept envisioned is built upon a deployable ultra-thin piezoelectric active thin shell architecture, with segmented tessellations. This vision is motivated by the need to deploy and control large, curved and precise surfaces for a variety of applications including future space telescopes, and is made possible by recent progress in ultra-thin high-performance composites and active material technologies. The thesis uses a combination of heuristic design, theoretical analysis, numerical modeling and novel experimental techniques to construct and validate proposed concepts for deployable piezoelectric thin shells.

Specifically, the thesis answers the following questions: i) How to design and manufacture precise, foldable and curved piezoelectric shells. ii) How to deploy these shells reliably and maintain shape correctability in the deployed state. iii) How to synthesize large, curved deployable surfaces with the aforementioned advantages. iv) How to characterize and predict the nonlinear behavior of piezoelectric materials and thin structures under high electric field actuation and large bending deformations. v) How to improve the shape stability of piezoelectric active thin shells under dynamic disturbances without introducing external sensors.

First, the thesis proposes new methodologies and design criteria to synthesize deployable, modular edge-supported thin shells based on a combination of origami-inspired folding patterns and spatial mechanisms. In contrast to traditional deployable surface designs, which attach rigid shells to deployable trusses, the proposed methodology enables concurrent folding of flat or curved shells along with the support structures. Starting from a basic module, a variety of deployable surface concepts are proposed through tessellations of the module.

A piezoelectric material unimorph architecture is further introduced, providing global curvature and shape correction capabilities. All components of the basic concept are validated through model prototyping and material folding tests, and it is discovered that both the ultra thin carbon fiber composites and piezoelectric ceramic materials can achieve a small folding radius without failure. A composite, doubly-curved foldable shell is also designed and manufactured while still maintaining low shape error. These efforts have led to a new family of deployable piezoelectric thin shell structures that integrate low areal density, high shape accuracy, and structural foldability to an unprecedented degree.

The thesis then tackles the challenge of estimating the actuation response and residual structural deformation of unimorph active thin shells under high electric field and large bending motion. A rate-independent, full field phenomenological constitutive model for a polycrystalline piezoelectric material is characterized experimentally. It successfully captures both the observed ferroelectric and ferroelastic domain switching effects. To overcome the difficulty of testing ultra thin piezoelectric plates, a set of novel characterization techniques is developed and implemented to measure the dielectric and mechanical responses of this material. The characterized material constitutive relation is implemented in an efficient model for estimating the structural response of unimorph thin shells under general electric and mechanical loading. The complete set of governing equations is integrated with a Backward-Euler algorithm, reproducing the measured responses of both the material and the structure under complex loading sequences.

Active vibration damping based on self-sensing piezoelectric thin shells is then analyzed and demonstrated on testbed. The self-sensing architecture removes redundant external sensors by making dual use of the piezoelectric layer of the active shell. An adaptive identification method with the associated hardware to track the evolution of field dependent piezoelectric capacitance is implemented, and a new identification strategy is proposed. Closed loop damping with in-situ capacitance adaptation is conducted in bench tests on self-sensing cantilever beams and achieves -12~dB attenuation at the resonance frequency. A highly efficient modeling technique for general self-sensing piezoelectric thin shell structures is proposed which is able to construct closed loop dynamic models based on the vibration eigenmodes and actuation responses obtained from commercial finite element software. These validated modeling techniques are extended to a multi-electrode doubly curved thin shell, where the improvements of shape stability under closed loop damping are evaluated through simulations. It is discovered that the electrode pattern of the self-sensing piezoelectric layer determines the damping performance under the specific boundary conditions of the shell.

Thesis Files