Bonding a linearly piezoelectric patch on a linearly elastic body

International audienc

Analysis of Elastic and Viscoelastic Smart Flexible and Foldable Systems

Smart or adaptive structures that use multifunctional materials to control the response of a structure have been of considerable interest in recent years. Some examples are foldable and flexible structures that can be actuated by non-mechanical stimuli (thermal, electrical, magnetic, solvent, light, etc.). This study presents analyses of smart flexible and foldable structures, such as slender beams and thin plates/shells integrated with distributed polarized piezoelectric patches. The studied smart flexible and foldable structures are undergoing large rotations and relatively small strains that are triggered by electro-mechanical actuations. The electric actuation is done by stimulating the bonded patches with electric voltages, while the mechanical actuation is in the form of prescribed external surface- and/or body forces. Both elastic and viscoelastic material responses are considered for the foldable and flexible host structures. For the behavior of piezoelectric material, a nonlinear electro-mechanical constitutive equation is taken into account to incorporate large electric field inputs. Two types of piezoelectric patches are considered, namely piezoelectric wafer and active fiber composites. The governing equation of the Reissner’s beam theory is first adopted in order to describe the large deformations of the flexible and foldable systems, and modified for the electro-active beams to derive analytical solutions. This study is then extended to 3-D deformation of plates and shells with considering bending and membrane stiffness subjected to large rotation and displacements. Co-rotational finite element method is used to numerically solve the governing equation of the smart flexible plates. Simulations of various shape changes in smart flexible and foldable systems are presented and parametric studies are also conducted in order to examine the effects of material and geometrical parameters on the overall performance of smart systems

Micro-nano biosystems: silicon nanowire sensor and micromechanical wireless power receiver

Silicon Nanowire-based biosensors owe their sensitivity to the large surface area to volume ratio of the nanowires. However, presently they have only been shown to detect specific bio-markers in low-salt buffer environments. The first part of this thesis presents a pertinent next step in the evolution of these sensors by presenting the specific detection of a target analyte (NT-ProBNP) in a physiologically relevant solution such as serum. By fabrication of the nanowires down to widths of 60 nm, choosing appropriate design parameters, optimization of the silicon surface functionalization recipe and using a reduced gate oxide thickness of 5 nm; these sensors are shown to detect the NT-ProBNP bio-marker down to 2ng/ml in serum. The observed high background noise in the measured response of the sensor is discussed and removed experimentally by the addition of an extra microfabrication step to employ a differential measurement scheme. It is also shown how the modulation of the local charge density via external static electric fields (applied by on-chip patterned electrodes) pushes the sensitivity threshold by more than an order of magnitude. These demonstrations bring the silicon nanowire-based biosensor platform one step closer to being realized for point-of-care (POC) applications. In the second half of the thesis, it is demonstrated how silicon micromechanical piezoelectric resonators could be tasked to provide wireless power to such POC bio-systems. At present most sensing and actuation platforms, especially in the implantable format, are powered either via onboard battery packs which are large and need periodic replacement or are powered wirelessly through magnetic induction, which requires a proximately located external charging coil. Using energy harnessed from electric fields at distances over a meter; comprehensive distance, orientation, and power dependence for these first-generation devices is presented. The distance response is non-monotonic and anomalous due to multi-path interferences, reflections and low directivity of the power receiver. This issue is studied and evaluated using COMSOL Multiphysics simulations. It is shown that the efficiency of these devices initially evaluated at 3% may be enhanced up to 15% by accessing higher frequency modes

Nonlinear cancellation of the parametric resonance in elastic beams: theory and experiment

A non-linear control strategy is applied to a simply supported uniform elastic beam subjected to an axial end force at the principal-parametric resonance frequency of the first skew-symmetric mode. The control input consists of the bending couples applied by two pairs of piezoceramic actuators attached onto both sides of the beam surfaces and symmetrically with respect to the midspan, driven by the same voltage, thus resulting into symmetric control forces. This control architecture has zero control authority, in a linear sense, onto skew-symmetric vibrations. The non-linear transfer of energy from symmetric motions to skew-symmetric modes, due to non-linear inertia and curvature effects, provides the key physical mechanism for channelling suitable control power from the actuators into the linearly uncontrollable mode. The reduced dynamics of the system, constructed with the method of multiple scales directly applied to the governing PDE’s and boundary conditions, suggest effective forms of the control law as a two-frequency input in sub-combination resonance with the parametrically driven mode. The performances of different control laws are investigated. The relative phase and frequency relationships are designed so as to render the control action the most effective. The control schemes generate non-linear controller forces which increase the threshold for the activation of the parametric resonance thus resulting into its annihilation. The theoretical predictions are compared with experimentally obtained results

Characterization of composite piezoelectric materials for smart joint applications

Piezoelectric materials have the ability to provide desired transformation from mechanical to electrical energy and vice versa. When a mechanical force is applied to the piezoelectric material an electrical voltage is generated and when an electrical voltage is applied to the piezoelectric material it gets strained or deformed. Owing to these characteristics piezoelectric materials can be used as a sensor, an actuator, as well as a power generation unit. The high brittleness property of the original piezoelectric material is one of the major constraints in using them in the engineering applications. In order to overcome this disadvantage the composite piezoelectric materials were developed. The piezoelectric fiber composite product is flexible and can sustain the extensive deformation without being damaged, and is compatible with the composite structures’ processing procedure; which makes it, an ideal material to be used as an embedded sensor & a force actuator within the composite structures. The smart joint can be designed to have the piezoelectric materials embedded in them, the piezoelectric materials can detect the various loads that act on the composite joint and could provide the required counter-balancing force to the excitation forces acting on the joint; and thereby could reduce or even eliminate the effects of stress concentrations at the composite joint. A high stress concentration is one of the principal causes of structural failures. In this work our main objectives are to study the sensing and force generation capabilities of various commercially available composite piezoelectric configurations through series of experimentations and to compare their performances in order to use them in the smart joint applications. Firstly, the sensing capabilities of these products were investigated at various input frequencies and amplitudes of the dynamic loads. Secondly, the tensile and bending force generation capabilities of these products were inspected with respect to various input excitation voltages. The results of these experiments depict that the voltage signals generated from these products are proportional to amplitudes of mechanical movement, with good response at high frequency, even at micrometer deformation domain; but the force generation is relatively low under the current input conditions and configuration under study

An Application of Optimized Bistable Laminates as a Low Velocity, Low Impact Mechanical Deterrent

This research considers the problem of using bistable laminates as a mechanical deterrent to the impending impact of a particle. The structure will be controlled through an algorithm that will utilize piezoelectric devices to activate them in unison with the bistable laminate to successfully deter. A novel experimental setup will be constructed to ensure that the bistable laminate stays fixed when acting as a mechanical deterrent. Piezoelectricity is the main driving force of the bistable laminate to morph and this study will use a Macro Fiber Composite (MFC) actuator that contains piezoelectric ceramic rods in a patch to transfer electrical energy into mechanical action. The bistability of the composite laminate is the ability to morph between two stable forms of the stacked laminate that will act as the moving element to deflect the incoming particle. The bistable mechanism containing the piezoelectric patch and bistable composite will undergo an optimization algorithm to maximize the chances of a successful deflection event. Having greater distance between states increases the chances of ensuring proper contact with the particle. Optimization can be utilized to maximize the total deflection between states of the bistable composite structure while also maximizing the piezoelectric limits. Areas that influence the bistable laminate such as deformation amount, edge lengths, and MFC patch compatibility will be included in the optimization algorithm. The MFC patch will influence the mechanism based on its active lengths and free strain. For this application-based approach, three different sizes of MFC piezoelectric patches will be used. Based on the particle\u27s characteristics, the timing of the bistable composite mechanism with the MFC patch will be rigorously studied to ensure proper deflection or reduction of impact through a Data Acquisition System and High Voltage Amplifier

Numerical Validation of Multiphysic Imperfect Interfaces Models

We investigate some mathematical and numerical methods based on asymptotic expansions for the modeling of bonding interfaces in the presence of linear coupled multiphysic phenomena. After reviewing new recently proposed imperfect contact conditions (Serpilli et al., 2019), we present some numerical examples designed to show the efficiency of the proposed methodology. The examples are framed within two different multiphysic theories, piezoelectricity and thermo-mechanical coupling. The numerical investigations are based on a finite element approach generalizing to multiphysic problems the procedure developed in Dumont et al. (2018)

Numerical Validation of Multiphysic Imperfect Interfaces Models

none4We investigate some mathematical and numerical methods based on asymptotic expansions for the modeling of bonding interfaces in the presence of linear coupled multiphysic phenomena. After reviewing new recently proposed imperfect contact conditions (Serpilli et al., 2019), we present some numerical examples designed to show the efficiency of the proposed methodology. The examples are framed within two different multiphysic theories, piezoelectricity and thermo-mechanical coupling. The numerical investigations are based on a finite element approach generalizing to multiphysic problems the procedure developed in Dumont et al. (2018).openDumont S.; Serpilli M.; Rizzoni R.; Lebon F.C.Dumont, S.; Serpilli, M.; Rizzoni, R.; Lebon, F. C