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This work proposes a novel methodology for planning the motion of fish-like soft robots actuated by macro-fiber composite (MFC) pairs. These structures should mimic oscillatory and undulation movements, which can be accomplished if the amplitude of the tail motion is larger than that of the head motion. Design strategies, such as the use of concentrated and distributed masses, are addressed to mimic fish-like motion since they guarantee suitable mode shapes for the structure. The motion planning proposal explores a model-based predictive control (MPC) strategy for deriving the input signals for the MFC actuators. This model-based control strategy requires the use of reasonably small-sized models. This is accomplished by extracting modal state-space models based on the free–free Euler–Bernoulli beam theory considering the electro-mechanical coupling of the MFC actuator pairs. Numerical results demonstrate the capability of the proposal for deriving bounded input signals that generate oscillatory and undulation movements even in the presence of disturbances. This general approach can be further extended for other applications. [ABSTRACT FROM AUTHOR]

Dynamic oscillating behavior of the flexible structure immerged in viscous fluids has attracted growing attention and been widely used in various practical applications. A general electricity-structure-fluid coupled model for the forced dynamic responses of a cantilever immersed in fluids, with partially distributed macro fiber composite, is proposed in this paper. Based on the classical Euler–Bernoulli beam theory, the first mass-normalized mode shape of the cantilever with partially bonded macro fiber composite is determined using assumed mode method. The attachment of the macro fiber composite actuators stiffens the macro fiber composite-bonded portion of the cantilever. The established mode shape matches perfectly with experimental results. Considering the macro fiber composite actuator as a set of representative elements connected in parallel, the internally actuation moment provided by the macro fiber composite actuators is obtained. The hydrodynamic load caused by the surrounding fluids, decomposed into the added mass and hydrodynamic damping parts, is also added to the theoretical model in the frequency-domain form. The predicted in-air and underwater dynamic behaviors of the flexible beam are consistent with the experimental results at different auction levels. Thus, the obtained general electricity-structure-fluid coupled model can be used to predict the forced dynamic responses of flexible structure with partially bonded actuators immersed in fluids. [ABSTRACT FROM AUTHOR]

Over the last decade, vibration energy harvesting has received substantial attention of many researchers. Piezoelectric materials are able to capture energy from ambient vibration and convert it into electricity which can be stored in batteries or utilized to power small electronic devices. In order to benefit from the 33-mode of the piezoelectric effect, interdigitated electrodes have been utilized in the design of macro fiber composites which are made of piezoelectric fibers of square cross sections embedded into an epoxy matrix material. This paper presents an analytical model of a macro fiber composite bimorph energy harvester using the 33-mode. The mixing rule is applied to determine the equivalent and homogenized properties of the macro fiber composite structures. The electromechanical properties of a representative volume element composed of piezoelectric fibers and an epoxy matrix between two successive interdigitated electrodes are coupled with the overall electro-elastodynamics of the harvester utilizing the Euler–Bernoulli theory. Macro fiber composite bimorph cantilevers with diverse widths are simulated for power generation when a resistive shunt loading is applied. Stress components in the Kapton layers, which are typically a part of any macro fiber composite patch, and in the bonding layers have been included in the model contrary to previously published studies. Variable tip mass, attached at the free end of the beam, is utilized in this paper to tune the resonance frequency of the harvester. The generated power at the fundamental short circuit and open circuit resonance frequencies of harvesters having three different widths is analyzed. It has been observed that higher electrical outputs are produced by the wider macro fiber composite bimorph using (M8528-P1 patches). [ABSTRACT FROM AUTHOR]

This article investigates the modeling of macro fiber composite-actuated laminate plates with distributed actuator patches. The investigation details an analytical and finite element modeling, with experimental validation of the bending strain and deflection of an epoxy E-glass fiber composite laminate. An analytical approach is also developed to estimate the plate deflection from the experimental strain measurements. The analytical method uses direct integration of single dimensional plate bending moments obtained by strain-induced shear moments from the macro fiber composite actuators. Finite element analysis software was used with the composite laminate modeled in ANSYS ACP. The results from both analytical and numerical models show good agreement with the experimental results, with strain values agreeing within 20 ppm and the maximum difference in deflection not exceeding 0.1 mm between models. Finally, an application of the analytical model for developing morphing aerofoil designs is demonstrated. [ABSTRACT FROM AUTHOR]

The elastic instabilities associated with buckling in bistable structures have been harnessed toward energy-based and motion-based applications, with significant research toward energy harvesting and morphing. Often combined with smart materials, structural prototypes are designed with a single application in mind. Recently, a novel method of inducing bistability was proposed by bonding two piezoelectrically actuated macro fiber composites in a [0MFC/90MFC]T layup and releasing the voltage post cure to yield two cylindrically stable configurations. Since the macro fiber composites are simultaneously the actuator and host structure, the resulting efficiencies enable this bistable laminate to be multifunctional, with both broadband energy harvesting and snap-through morphing capabilities. This article experimentally characterizes the vibration-based energy harvesting performance of the laminate to enable morphing. Through frequency sweeps across the first two modes of both states, the laminate exhibits broadband cross-well dynamics that are exploited for improved power generation over linear resonant harvesters. Besides single-well oscillations, snap-throughs are observed in intermittencies and subharmonic, chaotic, and limit cycle oscillations. The maximum power output of each regime and their charge durations of an energy harvesting module are assessed. The laminate’s capabilities are then bridged by utilizing harvested energy in the charged module to initiate snap-through actuation. [ABSTRACT FROM AUTHOR]

Aerothermoelastic flutter properties of nonlinear composite laminated panels in supersonic airflow are studied, and investigations on active flutter and aerothermal postbuckling suppression for the panels with time-dependent boundary conditions are also carried out using macro fiber composite actuator and sensor. The von Karman strain–displacement relation in conjunction with the supersonic piston theory is applied in structural modeling. Nonlinear dynamic equations of motion for the structural system are established using Hamilton’s principle and the assumed mode method. Frequency- and time-domain methods are used to investigate the aerothermoelastic characteristics and active flutter and aerothermal postbuckling suppression of the panels. Effects of aspect ratio and ply angle on the nonlinear aerothermoelastic behaviors are studied. The displacement feedback control is used to conduct the active flutter and postbuckling suppression. The nonlinear output controller consisting of a linear quadratic regulator and a nonlinear state estimator of extended Kalman filter is also used in designing the controller. Controlled vibration responses of the structural system under the two different controllers are compared. The results show that the developed linear quadratic regulator/extended Kalman filter controller is more effective than the displacement feedback control controller in flutter and postbuckling control of the panels with time-dependent boundary conditions in supersonic airflow. [ABSTRACT FROM AUTHOR]

Impact damage has been identified as a critical form of defect that constantly threatens the reliability of composite structures, such as those used in aircrafts and naval vessels. Low-energy impacts can introduce barely visible damage and cause structural degradation. Therefore, efficient structural health monitoring methods, which can accurately detect, quantify, and localize impact damage in complex composite structures, are required. In this article, a novel damage detection methodology is demonstrated for monitoring and quantifying the impact damage propagation. Statistical feature matrices, composed of features extracted from the time and frequency domains, are developed. Kernel principal component analysis is used to compress and classify the statistical feature matrices. Compared with traditional principal component analysis algorithm, kernel principal component analysis method shows better feature clustering and damage quantification capabilities. A new damage index, formulated using the Mahalanobis distance, is defined to quantify impact damage. The developed methodology has been validated using low-velocity impact experiments with a sandwich composite wing. [ABSTRACT FROM PUBLISHER]

This article focuses on the modeling of structures equipped with Macro Fiber Composite (MFC) transducers. Based on the uniform field method under the plane stress assumption, we derive analytical mixing rules in order to evaluate equivalent properties for d31 and d33 MFC transducers. In particular, mixing rules are derived for the longitudinal and transverse piezoelectric coefficients of MFCs. These mixing rules are validated using finite element computations and experimental results available from the literature. [ABSTRACT FROM AUTHOR]

A Shear Actuated Fiber Composite (SAFC) concept is developed that may find application in structural actuation and health monitoring tasks. The fabrication aspects of SAFC are briefly discussed. A uniform field model is employed to study electro-elastic behavior of the SAFC. The composite actuator is modeled as a general laminate having seven layers, and the effective properties are evaluated further using shear deformation lamination theory. The geometric parameters such as fiber volume fraction, fiber thickness, and fiber orientation are considered, and their influence on the characteristics of SAFC is analyzed. It is observed that a higher fiber thickness may provide better shear actuation capability for the SAFC actuator; but conformability requirements bring a constraint on fiber thickness that needs to be optimized. A fiber volume content of 85–95% appears to provide a design envelope for the SAFC actuator. SAFC has shown a promising feature of simultaneously coupling both transverse shear strains, if the poled PZT fibers are oriented directionally. Therefore, SAFC can be used as a torsional actuator for developing electro-elastically tailored smart laminated or sandwich structures. It is also expected that the SAFC actuator may provide a better solution for active aeroelastic control applications, where torsion mode is critical. [ABSTRACT FROM AUTHOR]

A nonlinear model for a piezoelectric continuum subjected to a monotonic increase in electric field under constant mechanical load is investigated. A general model is derived and then specialized for a piezoceramic-based material with anisotropic actuation and mechanical properties, for example, the Macro Fiber Composite (MFC) actuator. This formulation includes the linear-elastic mechanical response, as well as linear and second-order piezoelectric behavior and a second-order electromechanical cross-term. Using previously published work by the same authors (Williams, R.B., Inman, D.J. and Wilkie, W.K. 2004. ‘Tensile and Shear Behavior of Macro Fiber Composite Actuators,’ Journal of Composite Materials, 38(10):855-870) dealing with the mechanical response of the MFC, this set of material properties is determined experimentally in order to characterize the response of this device to given external loading conditions. [ABSTRACT FROM AUTHOR]

The design, fabrication, and testing of a flexible, laminar, anisotropic piezoelectric composite actuator utilizing machined PMN-32%PT single-crystal fibers is presented. The device consists of a layer of rectangular single-crystal piezoelectric fibers in an epoxy matrix, packaged between interdigitated electrode polyimide films. Quasistatic free- strain measurements of the single-crystal device are compared with measurements from geometrically identical specimens incorporating polycrystalline PZT-5A and PZT-5H piezo-ceramic fibers. Free-strain actuation of the single-crystal actuator at low bipolar electric fields (±250 V/mm) is ≈400% greater than that of the baseline PZT-5A piezoceramic device, and 200% greater than that of the PZT-51-I device. Free-strain actuation under high unipolar electric fields (0-4 kV/mm) is ≈200% of the PZT-5A baseline device, and 150% of the PZT-5H alternate piezoceramic device. Performance increases at low field are qualitatively consistent with predicted increases based on scaling the low-field d33 piezoelectric constants of the respective piezoelectric materials. High-field increases are much less than scaled d33 estimates, but appear consistent with high-field free-strain measurements reported for similar bulk single-crystal and piezoceramic compositions. Measurements of single-crystal actuator capacitance and coupling coefficient are also provided. These properties were poorly predicted using scaled bulk material dielectric and coupling coefficient data. Rule-of-mixture calculations of the effective elastic properties of the single-crystal device and estimated actuation work energy densities are also presented. Results indicate longitudinal stiffnesses significantly lower (50% less) than either piezoceramic device. This suggests that single-crystal piezocomposite actuators will be best suited to low induced-stress, high strain, and deflection applications. [ABSTRACT FROM AUTHOR]

The use of piezoelectric ceramic materials for structural actuation is a fairly well-developed practice that has found use in a wide variety of applications. However, just as advanced composites offer many benefits over traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers can improve upon many of the limitations encountered with monolithic piezoceramic devices used to control structural dynamics. This paper discusses the Macro Fiber Composite (MFC) actuator, which utilizes piezoceramic fibers, for example, lead zirconate titanate (PZT), embedded in an epoxy matrix for structural actuation. An overview of the MFC assembly process is presented, followed by a cure kinetics model that describes the behavior of the thermosetting epoxy matrix. This empirical model is seen to agree closely with the experimental data. [ABSTRACT FROM AUTHOR]