This study examines the biomimicry of wave propagation, a mode of locomotion in aquatic life for the use-case of morphing aircraft surfaces for boundary layer control. Such motion is theorized to inject momentum into the flow on the upper surface of airfoils, and as a consequence, creates a forcible pressure gradient thereby increasing lift. It is thought that this method can be used to control flow separation and reduce likelihood of stall at high angles of attack. The motivation for such a mechanism is especially relevant for aircraft requiring abrupt maneuvers, and especially at high angles of attack as a safety measure against stalling. The actuation mechanism consists of lightweight piezoelectric ceramic transducers placed beneath the upper surface of an airfoil. An open-loop system controls surface morphing. A two-dimensional Fourier Transform technique is used to estimate traveling to standing wave ratio, which is verified analytically using Euler Bernoulli beam theory, and experimentally using a prototype wing. Propagating wave control is tuned and verified using a series of scanning laser vibrometry tests. A custom two-dimensional NACA 0018 airfoil tests the concept in a low-speed wind tunnel with approximate Reynolds Number of 50,000. Both traveling waves and the changes in lift and drag will be experimentally characterized.

Steady-state traveling waves in structures have been previously investigated for a variety of purposes including propulsion of objects and agitation of a surrounding medium. In the field of additive manufacturing, powder bed fusion (PBF) is a commonly used process that uses heat to fuse regions of metallic or polymer powders within a loose bed. PBF processes require post-process removal of loose powder, which can be difficult when blind holes or complex internal geometry are present in the fabricated part. Here, a preliminary investigation of a simple part is conducted examining the use of traveling waves for post-process de-powdering of additively manufactured specimens. The generation of steady-state traveling waves in a structure is accomplished through excitation at a frequency between two adjacent resonant frequencies of the structure, resulting in two-mode excitation. This excitation can be generated by bonded piezoceramic elements actuated by a sinusoidal voltage signal. The response of the structure is affected by the parameters of the excitation, such as the particular frequency of the voltage signal, the placement of the piezoceramic actuators, and the phase difference in the signals applied to different actuators. Careful selection of these parameters allows adjustment of the quality, wavelength, and wave speed of the resulting traveling waves. In this work, open-top rectangular box specimens composed of sintered nylon powder and coated with fine sand are used to represent freshly fabricated parts yet-to-be cleaned of un-sintered powder. Steady-state traveling waves are excited in the specimens while variations in the frequency content and phase differences between actuation points of the excitation are used to affect the characteristics of the dynamic response. The effectiveness of several response types for the purpose of moving un-sintered nylon powder within the specimens is investigated.

We explore the modeling and analysis of nonlinear non-conservative dynamics of macro-fiber composite (MFC) piezo-electric structures, guided by rigorous experiments, for resonant vibration-based energy harvesting, as well as other applications leveraging the direct piezoelectric effect, such as resonant sensing. The MFCs employ piezoelectric fibers of rectangular cross section embedded in kapton with interdigitated electrodes to exploit the 33-mode of piezoelectricity. Existing frameworks for resonant nonlinearities have so far considered conventional piezoceramics that use the 31-mode of piezoelectricity. In the present work, we develop a framework to represent and predict nonlinear electroelastic dynamics of MFC bimorph cantilevers under resonant base excitation. The interdigitated electrodes are shunted to a set of resistive electrical loads to quantify the electrical power output. Experiments are conducted on a set of MFC bimorphs over a broad range of mechanical excitation levels to identify the types of nonlinearities present and to compare the model predictions and experiments. The experimentally observed interaction of material softening and geometric hardening effects, as well as dissipative effects, is captured and demonstrated by the model.

The Maximum Entropy (ME) method is shown to provide a new approach for quantifying model uncertainty in the presence of complex, heterogeneous data. This is important in model validation of a variety of multifunctional constitutive relations. For example, multifunctional materials contain field-coupled material parameters that should be self-consistent regardless of the measurement. A classical example is piezoelectricity which may be quantified from charge induced by stress or strain induced by an electric field. The proposed tools provide new statistical information to address measurement discrepancies, guide model development, and catalyze materials discovery for data fusion problems. The error between the model outputs and heterogeneous data is quantified and used to formulate a second moment constraint within the entropy functional. This leads to an augmented likelihood function that weights each individual set of data by its respective variance and covariance between each data set. As a first step, the method is evaluated on a piezoelectric ceramic to illustrate how the covariance matrix influences piezoelectric parameter estimation from heterogeneous electric displacement and strain data.

Additive Layer Manufacturing is offering tremendous oportunities for manufacturing. Many complex structures, which could not be manufactured by conventional methods can be produced additive. This paper gives three examples of how additive manufacturing can be used to built smart structures with integrated actuators and sensors. The integration of piezoceramic actuators into FDM and SLM processes is described as well as the design of structures with integrated pneumatic actuators printed with the PolyJet method.

This study will present a proof-of-concept non-contact strain sensor, utilizing a prototype magnetostrictive (Fe-Ga alloy, Galfenol) strip on a steel plate; coupled mechanical-magnetostrictive equations will be used to evaluate sensor performance prediction. In contrast with typical piezo-ceramic materials, Galfenol is ductile and has an excellent ability to withstand mechanical shock. Galfenol also changes its permeability in response to applied stress. This stress-based permeability change is not time dependent and can measure static loads. The variation of magnetic induction with stress depends strongly on bias magnetic field. Typically, the performance of Galfenol is measured in a compressional load region because it has higher response there. However, in this study, we are aiming to develop a sensor for tensile stress measurement. To achieve a compression load in the sensing element, a Galfenol strip is aligned perpendicular to a tension bar, so that tension in the bar creates compression in the strip, via the Poisson effect. The experimental setup in this study consists of a polycrystalline Galfenol strip bonded in the horizontal direction of a steel dog-bone shaped tension specimen. Two permanent magnets are attached at both ends of the Galfenol strip to provide a magnetic bias field through the strip. The magnetic flux through the Galfenol strip is measured with a non-contact Hall sensor during the tensile load test. The design reported here aims at low frequency applications, such as static and dynamic tension monitoring.

Impedance-based structural health monitoring (SHM) is a non-destructive, active technique for real-time structural damage assessment. Conventional impedance-based SHM practices apply a sinusoidal signal of fixed amplitude to excite the piezoceramic patch and obtain the impedance signature over a certain frequency range. Damage is then detected by comparing the measured impedance signature to a baseline measurement taken at the pristine state. In this work, the amplitude of the driving signal, which is directly related to the magnitude of the excitation force acting on the structure, is introduced as an additional variable, and sweeps over both frequencies and amplitudes are performed. Several structural defects, such as cracks and loose joints, are nonlinear in nature. Therefore, changing the excitation force will allow the detection of such damage induced nonlinearities and track their evolution. Numerical simulations are carried out to study the effects of nonlinearities on the impedance signature using a single mode model. Several types of structural nonlinearities, such as hardening, softening, and nonlinear damping are studied with the assumption that the piezoelectric actuator stays in its linear regime. Experiments are conducted on a single beam and a lap joint, and impedance signatures in the range of 12–15 KHz are measured at different levels of excitation. Nonlinear damping and softening behavior are detected experimentally by examining the measured impedance signatures. Numerical and experimental findings suggest the possibility of detecting and tracking structural nonlinearities using impedance measurements.

Previous work has demonstrated that piezoceramics are capable of generating net wave propagation without reflections in one-dimensional structures. The investigation into cylindrical traveling waves provides insight into unique dynamics (i.e., symmetric and non-symmetric modes) that have yet to be fully defined for two and three dimensional systems. The work herein will focus on the generation and characterization of traveling waves that propagate along the circumferential direction. The coupled system, given by a free-free cylinder with multiple piezoelectric actuator (PZT) patches, is used to evaluate several traveling wave modes in the cylinder. The use of structurally integrated piezoelectric patches as actuators has many advantages over the conventional shakers. Apart from the small, low weight, low cost and the size of these ceramic plates, PZTs can also generate waves over a wide frequency range. The use of multiple PZTs can be leveraged to excite the systems at a given frequency with a defined phase difference between them in order to generate highly controlled directional traveling waves in the cylindrical structure without reflections. Finite Element Modeling (FEM), in conjunction with experiments, were conducted to provide a comprehensive understanding of the generation and propagation behavior of the traveling wave modes in a thin walled cylinder.

Due to their very high applicable forces, frequencies and their stiffness, piezoceramics are feasible to serve as integrated actuators in machines. The application of piezo based components in production engineering was subject of plenty of investigations in the past. That focuses primarily on systems for condition monitoring, structural vibration reduction or chatter prevention. However there are currently also few approaches that aim to use piezo actuators for directly induced vibrations for improved machining processes. In this paper we present an overview of such systems, their parameters and the technological background. Known approaches will be classified and divided into groups considering their working principles, actuator performance and application technology. Ultra sonic machining (USM) for example is a comparatively old approach which applies ultrasonic vibrations of a sonotrode to an abrasive slurry for machining hard, brittle and nonconductive material. Vibration assisted machining (VAM) systems are rather different. They are characterized by low stroke, uncontrolled but highly frequent resonant vibrations of the tool to achieve enhanced chipping behavior or generally enable to machine certain hard materials. Fast Tool servo (FTS) systems are even more complex. They apply an overlaid controlled movement of the cutting edge to manufacture microstructures or possess to manufacture complex geometries like non circular bores or turned parts. Selected systems will be presented in detail showing their design approach, actuator parameters, control considerations and measurement data of manufactured parts. These will be for instance an ultrasonic deep hole drilling tool, a form honing system, an active spindle mounting for micro contouring and a piezo based machine table for manufacturing non circular bores in small workpieces. Summarized the existing systems will be compared considering their advantages and eventual hindrances. Beyond that the outlook will show problems, which need to be solved in the future to enable piezo assisted machining systems a more comprehensive application in manufacturing.

This paper describes a proof-of-concept non-contact strain sensor, using a magnetostrictive Fe-Ga alloy (Galfenol). Magnetostrictive materials demonstrate dimensional changes in response to a magnetic field. In contrast with typical piezoceramic materials, Galfenol is the most ductile of the current transduction materials and appears to have an excellent ability to withstand mechanical shock and tension. Galfenol also exhibits the inverse (Villari) effect: both the magnetization and permeability change in response to an applied stress. Galfenol has low hysteresis loses, less than ∼10% of its transduction potential over a range of −20 to +80 °C. The magnetization’s response to stress depends strongly on both magnetic field bias and alloy composition. Galfenol’s Villari effect can be used in various sensor configurations together with either a giant magnetoresistance (GMR) sensor, Hall Effect sensor or pickup coil to sense the magnetization / permeability changes in Galfenol when stressed. The sensor described in this paper utilizes the permeability change, which is not time dependent and can measure static loads. The design reported here targets low force, low frequency applications, such as inclination measurements and stress monitoring. The sensor was able to measure both static and dynamic stress. The static sensitivity was +3.64 Oe/kN for the Hall sensor close to the bias magnet and −1.49 Oe/kN for the Hall sensor at the other end of the Galfenol strip. We conclude that a Galfenol strain sensor is a viable candidate for bolt stress monitoring in critical applications.

Piezoceramic Patches are commonly used as actuator devices in smart structures if the induced forces are sufficient for the application. To model these devices in a structural dynamics simulation, a finite element model can be augmented by active layers. This needs a suitable element meshing, taking care of the actual shapes and positions of the active patches in use. If many different setups have to be evaluated, which is naturally the case for placement strategies for suitable actuator positions, this approach is quite cumbersome. To ease and speed up the augmentation of fixed finite element models with piezoceramic patches, so called modal correction methods have been successfully used in this context. These approximative methods avoid the remeshing and the reassembling of the underlying finite element model by adapting the modal description of the structural model with the mass, stiffness and electrical coupling effects of the applied patches. In this paper different aspects of this modelling approach are discussed especially for a tool chain to optimize patch locations in an ASAC simulation environment.

In the field of smart structures, piezoceramic actuators are wildly used for vibration reduction and acoustic manipulation of structures. Those applications typically run at frequencies between 10 Hz and 10k Hz. Prominent examples are the piezoceramic actuators implemented in helicopter rotor blades to twist them dynamically for higher harmonic control (HHC) or individual blade control (IBC). Once the actuators are implemented it would be a great benefit to also use them to statically change the blade twist (higher twist for take-off and landing — for higher lift; lower twist for high speed forward flight — for reduced drag). Staying with this example it can be found that sensing the twist displacement is not an easy task at all (see [1, 2]), so it would be most desirable, to use open loop control. In order to do that, the transfer function has to be known accurately. Unfortunately measurements show that the amplitudes for such very low frequencies behavior behave strongly non linear. This paper presents experimental results investigating the influence of the frequency on the amplitude — especially going for frequencies in the lower mHz region. A variety of piezoceramic actuators has been investigated: from stacks to patch type, d 33 as well as d 31 effect actuators. A second focus of this paper is the reaction of piezoceramic actuators on the application of a constant DC voltage. The drift that occurs has to be taken into consideration. A third focus of this paper is the dependency of a displacement output of such an actuator at a constant applied DC voltage on the voltages that the actuator had seen before. This topic is of special importance for aerodynamically effective surfaces that are driven by piezoceramic actuators and should be analyzed (generation of polars) in static conditions.

Shape Memory Alloys (SMAs) are active metallic materials classified as “smart” or “intelligent” materials along with piezoelectric ceramic and polymers, electro-active plastics, electro-rheological and magneto-rheological fluids and others. SMAs show a multitude of different and dependent properties interesting for technological applications. These properties depend on the peculiar deformation mechanisms, accounting for the so-called shape memory effect. SMAs are nowadays used in quite different fields, like thermo-mechanical devices, anti-loosening systems, biomedical applications, mechanical damping systems, in some cases employed for large scale civil engineering structures. These multifunctional materials can be naturally considered as sensor-actuator elements demonstrating large possibilities for applications in high-tech smart systems. The use of SMAs in actuators offers an excellent technological opportunity to develop reliable, robust, simple and lightweight elements within structures or as stand-alone components that can represent an alternative to electro-magnetic actuators commonly used in several fields of industrial applications, such as automotive, appliances, consumer electronics and aerospace. NiTi-based SMAs demonstrated to have the best combination of properties, especially in terms of the amount of work output per material volume and the large amount of recoverable stress and strain. However, there are several limiting factors to a widespread diffusion of SMAs to technological fields. For instance, SMAs display a critical dependence of the shape-memory related properties, like transition temperatures, on their actual composition. For this reason, a great care in the production steps, mainly based on casting processes, is required. Another critical aspect, that is to be considered when dealing with SMAs, is the strong influence of their thermo-mechanical history on their properties. This may disclose interesting perspectives of application to smart devices in which different aspects of the shape memory phenomenology, like one and two way shape memory effect, pseudoelasticity, damping capacity, etc., are used. Last, but not least, one of the most debated aspects around NiTi alloys is microcleanliness. This concept is becoming increasingly important as the industrial market moves to smaller, lower profile devices with thinner structures. In this work a general overview about the peculiar behavior of NiTi alloys along with their main issues, the shape memory components under development, and the main efforts and directions for materials improvement will be presented and discussed. A bird’s-eye view on the future opportunities of NiTi-based shape memory actuators for industrial applications will also be given.

Vibration-based energy harvesting has drawn significant attention from different engineering disciplines over the last two decades. The studies in this research area have mostly concentrated on cantilevered piezoelectric beam harvesters under base excitations. As an alternative to beam arrangements, patch-based piezoelectric energy harvesters can be integrated on large plate-like structures such as panels of automotive, marine and aerospace applications to extract useful electrical power during their operation. In this paper, electroelastic finite element (FE) simulations of a patch-based piezoelectric energy harvester structurally integrated on a panel of a heavy duty vehicle are presented during different phases of operation. FE model of the panel together with a piezoceramic harvester patch is built using ANSYS software. The FE model takes into account coupled electromechanical dynamics and the fully-conductive electrode layers of the harvester patch. The vibration response of the panel as well as the voltage output of the harvester patch under operating conditions is simulated using the forces obtained from experimental measurements on the heavy duty vehicle. Excitation forces are calculated from operational acceleration measurements using matrix inversion method, which is a force identification technique. Two different operating conditions of the heavy duty vehicle are considered: stationary and moving on a test track while the engine was running. Using the excitation forces in the FE simulations, the electrical power generation of the harvester patch is predicted for a wide range of resistive loads. Electrical power outputs are then presented for short-circuit and open-circuit conditions. The numerical results show that the use of a harvester patch attached on a panel of a heavy duty vehicle generates reasonably well electrical power outputs.

The hair cells in the cochlea are responsible for transforming sound-induced vibration into electrical signals. Damage to these hair cells is among the most common forms of hearing loss in the developed world. Researchers have studied various artificial hair cell (AHC) designs for replacing these hair cells. One such method uses piezoelectric beams to mimic the hair cell’s mechanoelectrical transduction. A piezoelectric beam will produce an electric potential from an applied sound pressure. In the literature, the response of the cochlea to sound pressures is often described using tuning curves. Tuning curves plot the sound pressure level at a given frequency which produces a particular displacement, velocity, or neuron firing rate. The work presented here examines using piezoelectric AHC’s to mimic cochlear hair cells by creating tuning curves of constant tip velocity and voltage. A piezoceramic (PZT) beam and a piezo film (PVDF) bending sensor are examined. An output feedback controller based on PID control is developed to vary the sound pressure from a speaker to create tuning curves for the piezoelectric AHC’s. The tuning curves for the piezoelectric beams are compared to measurements obtained from the biological cochlea.

In this paper, the modeling and analysis of a nonlinear rectangular plate-like wing with embedded piezoceramics is presented for aeroelastic energy harvesting. The nonlinear electromechanical finite-element plate model is based on the von Karman plate assumptions while the unsteady aerodynamic model uses the doublet-lattice method (originally in frequency domain). The aerodynamic model is converted to the time domain by using Roger’s approximation. A load resistance is considered in the electrical domain of the problem. The set of nonlinear equations is solved with the iterative Newton-Raphson method and the generalized alpha method is used to numerically integrate the equations. Five different wing configurations with aspect ratios varying from one to five are investigated. The effect of the aspect ratio on the linear aeroelastic behavior is first investigated for the short circuit condition. Later, the nonlinear electroaeroelastic behavior is investigated for a range of load resistances and the different aspect ratios of the linear case. The effects of aspect ratio and load resistance on the cut-in speed of limit cycle oscillations (LCOs), on the range of airflow speeds of LCOs of acceptable amplitudes and also on the mechanical and electrical outputs of the generator are investigated.

The inner hair cells (IHC’s) and outer hair cells (OHC’s) in the cochlea are vital components in the process of hearing. The IHC’s are responsible for converting sound-induced vibration into electrical signals. The OHC’s produce forces that amplify these vibrations and therefore enhance the electrical signals produced by the IHC’s. The resulting “cochlear amplifier” produces a nonlinear amplification which gives the ear its ability to detect sound pressure levels ranging from 20 μPa to 20 Pa (0 to 120 dB). This paper presents the modeling and testing of an artificial hair cell (AHC) piezoelectric sensor inspired by the hair cells found in the mammalian ear. The sensor is a bimorph cantilever beam consisting of a sensing piezoceramic element and an actuating piezoceramic element bonded to a brass substrate. The sensing element is used to detect the mechanical motion of the beam. Output feedback control can be used to send a voltage signal to the actuating element and alter the frequency response of the beam. A control law, which modifies the linear damping term of the first mode and introduces cubic damping, is used to create a closed-loop system perched at a Hopf bifurcation. The result is a system that produces a nonlinear amplification of the beam’s mechanical response in a manner which mimics the nonlinear behavior of the mammalian cochlea. This active sensor is studied under base acceleration and the initial test results are compared to a finite element model. Simulations of the closed-loop system are examined for the system with a single mode and for the system with multiple modes.

This paper describes new active composite structures based on thermoplastic matrices which contain material homogeneous embedded piezoceramic modules. Starting point is the development of novel thermoplastic compatible piezoceramic modules, so called TPMs. By the utilization of the same matrix material for the composite structure and for the TPM carrier films, these modules afford an opportunity to become directly embedded into the component during its manufacturing process. In this context, the manufacturing technology of the TPMs and of the active composite structure is presented. Furthermore, selected test samples are investigated concerning their modal behavior. Based on the determined characteristics a linear two-port model is used for the reproduction of the experimental results.

Lead zirconate titanate (PZT) and Shape memory alloys (SMA) smart composites have been previously investigated for use as actuators. SMAs exhibit a high actuating strain but responds slowly, while PZTs supply small actuation with a fast response. The composite can be tailored to control its shape when subjected to different loads, thus leading to multiple functions actuators. In this study, the concept is applied in the design of energy harvesting devices for self-tuning and control of the output response. The material type and the composite fractions properties can be optimized to tune the system’s response in order to achieve maximum output and to compensate for the external environmental effects such as temperature. In this paper, the energy harvesting capabilities of a cantilevered composite beam, containing piezoelectric ceramic and shape memory alloy cylindrical inclusions, are studied. The system is subject to base excitation input load. Only non-prestrained SMA inclusions are considered. A model based on the mean field theory, linear piezoelectricity, and one dimensional constitutive behavior of shape memory alloys is developed to describe the effect of SMA inclusions on the time and the frequency response of the composite. The PZT and the matrix behaviors are considered linear. The overall response of the composite is highly non-linear due to the phase transformation within the SMA inclusions. A preliminary analysis of the variations of the frequency response, the time response, the power output, and the efficiency of the device with respect to the materials fractions is presented. The temperature effects are also investigated.

This manuscript considers the design and performance of a piezoelectric vibration-based energy harvester with a dynamic magnifier (VEHDM) to a traditional single degree-of-freedom harvester (VEHS) using proper metrics. Past research has shown that the addition of the second magnifying mass can increase the peak power harvested by as much as 20 times [1] when compared to the VEHS; however, the metrics of performance comparison were not clearly defined, nor was the comparison carried at optimal loading conditions. For instance, the peak power was compared at different excitation frequencies and power not power per unit mass is used for comparison purposes. Additionally, the VEHDM is designed so that the magnifier mass and stiffness are considered independent of the primary stiffness and mass of the harvester. In this study, we determine the optimal properties of the magnifier, in terms of frequency ratios and resistance that maximizes both power and power density for a fixed frequency harmonic excitation. The optimized VEHDM is compared to a similarly optimized VEHS. Treating the magnifier as a tuned mass damper (TMD), i.e., simply adding the magnifying mass and stiffness to the optimized VEHS and then tuning the magnifier to split the resonance peak of the single mass harvester, increases the peak power harvested for mass ratios greater than one. However, the peak frequencies of excitation of the VEHS and VEHDM differ. Only at large values of the mass ratio does the excitation frequency of the VEHS and VEDHM coincide, making the VEHDM less efficient in terms of power per unit mass. Similarly, simply adding a magnifying stiffness and mass to the optimized VEHS and then tuning both the VEDHM to the VEHS’s to the same excitation frequency by changing the the uncoupled natural frequency of VEHDM’s magnifier components limits the performance of the VEDHM. In this case, the VEHDM generates the same amount of power as the VEHS. Nonetheless, the VEHS is more efficient in terms of power generated per unit mass. In order to match the single mass harvester’s power per unit mass, the optimal magnifier for the VEHDM is a rigid spring of negligible mass acting in series with the stiffness with the VEHDM’s piezoceramic element. However, significant gains in both peak power and peak power per unit mass for a fixed frequency excitation can be obtained by considering all the mass and stiffness elements in the VEHDM, while using the same piezoelectric in the VEHS.