Oliver Myers

Numerical Modeling of a Circularly Interdigitated Piezoelectric Microactuator

Accurate modeling and simulation techniques are vital for actuated membranes. Using multiphysical modeling techniques, coupled with variation in design parameters, accurate performance predictions can be realized. A 2-D axis-symmetric model of a circularly interdigitated piezoelectrically membrane is presented. The model includes the piezoelectric material and properties, as well as the membrane materials and properties, and incorporates various design considerations. This model also includes the electromechanical coupling for piezoelectric actuation and highlights a novel approach to take advantage of the higher d33 piezoelectric coupling coefficient. Changes in parameters, including electrode pitch, electrode width, and piezoelectric material thickness, are evaluated.

Damage detection of unidirectional carbon fiber–reinforced laminates with embedded magnetostrictive particulates: A preliminary study

Defects in composite laminates are difficult to detect because of the conductive and paramagnetic properties of composite materials. Timely detection of defects in composite laminates can improve reliability. This research illustrates the preliminary analysis and detection of delaminations in carbon fiber laminate beams using a single layer of magnetostrictive particles and noncontacting concentric magnetic excitation and sensing coils. The baseline analytical models also begin to address the intrusive nature of the magnetostrictive particles as well as relate the applied excitation field with the stress and magnetic flux densities induced in the magnetostrictive layer. Numerical methods are used to begin to characterize the presence of magnetostrictive particles in the laminate and the behavior of the magnetostrictive particles in relationship to the magnetic field used during sensing. Unidirectional laminates with embedded delaminations are used for simulations and experimentations. A novel, yet simplified fabrication method is discussed to ensure consistent scanning and sensing capabilities. The nondestructive evaluation scanning experiments were conducted with various shapes and sizes of damages introduced into carbon fiber–reinforced polymeric composite structures. The results demonstrate high potential for magnetostrictive particles as a low-cost, noncontacting, and reliable sensor for nondestructive evaluation of composite materials.

Modeling Bistable Composite Laminates for Piezoelectric Morphing Structures

A sequential modeling effort for bistable composite laminates for piezoelectric morphing structures is presented. Thin unsymmetric carbon fiber composite laminates are examined for use of morphing structures using piezoelectric actuation. When cooling from the elevated cure temperature to room temperature, these unsymmetric composite laminates will deform. These postcure room temperature deformation shapes can be used as morphing structures. Applying a force to these deformed laminates will cause them to snap through to another shape. This bistability arises from the fabrication process of the thin unsymmetric laminates. The snap through force studied here will be controlled by using piezoelectricity. Macrofiber composite (MFC) actuators are used for piezoelectric actuation. In this research, an analytical modeling method is presented to accurately depict the piezoelectric morphing structures. Sequential numerical modeling of the cure process to account for residual stresses and postcured shapes and piezoelectric morphing structure is done to predict the piezoelectric actuated displacements of the thin unsymmetric composite laminates. Analytical and numerical models are compared to experimental methods and results.

Design and simulation of PZT-based MEMS piezoelectric sensors

Devices with increased sensitivities are needed for various applications including the detection of chemical and biological agents. This paper presents the design of microelectromechanical systems (MEMS) devices that incorporate lead zirconate titanate (PZT) films in order to realize highly sensitive sensors. In this work, the piezoelectric properties of the PZT are exploited to produce sensors that perform optimally for mass sensing applications. The sensor is designed to operate as a thin-film bulk acoustic resonator (TFBAR) whereas a piezoelectric is sandwiched between electrodes and senses a change in mass by measuring a change in resonance frequency. Modeling of the TFBAR sensor, using finite element analysis software COMSOL, was performed to examine optimal device design parameters and is presented in this paper. The effect of the PZT thickness on device resonance is also presented. The piezoelectric properties of the PZT is based on its crystal structure, therefore, optimization of the PZT film growth parameters is also described in this work. A detailed description of the fabrication process flow developed based on the optimization of the device design and film growth is also given. The TFBAR sensor consists of 150 nm of PZT, 150nm of silicon dioxide, silicon substrate, titanium/platinum bottom electrodes, and aluminum top electrodes. The top electrodes are segmented to increase the sensitivity of the sensor. The resonance frequency of the device is 3.2 GHz.

Comparative analysis of the planar capacitor and IDT piezoelectric thin-film micro-actuator models

A comparison of the analysis of similarly developed microactuators is presented. Accurate modeling and simulation techniques are vital for piezoelectrically actuated microactuators. Coupling analytical and numerical modeling techniques with variational design parameters, accurate performance predictions can be realized. Axi-symmetric two-dimensional and three-dimensional static deflection and harmonic models of a planar capacitor actuator are presented. Planar capacitor samples were modeled as unimorph diaphragms with sandwiched piezoelectric material. The harmonic frequencies were calculated numerically and compared well to predicted values and deformations. The finite element modeling reflects the impact of the d31 piezoelectric constant. Two-dimensional axi-symmetric models of circularly interdigitated piezoelectrically membranes are also presented. The models include the piezoelectric material and properties, the membrane materials and properties, and incorporates various design considerations of the model. These models also include the electro-mechanical coupling for piezoelectric actuation and highlight a novel approach to take advantage of the higher d33 piezoelectric coupling coefficient. Performance is evaluated for varying parameters such as electrode pitch, electrode width, and piezoelectric material thickness. The models also showed that several of the design parameters were naturally coupled. The static numerical models correlate well with the maximum static deflection of the experimental devices. Finally, this paper deals with the development of numerical harmonic models of piezoelectrically actuated planar capacitor and interdigitated diaphragms. The models were able to closely predict the first two harmonics, conservatively predict the third through sixth harmonics and predict the estimated values of center deflection using plate theory. Harmonic frequency and deflection simulations need further correlation by conducting extensive iterative harmonic simulations and experiments. The results, conclusions and potential improvements are discussed.

Two Tiered Analysis of a CFRP Laminate Imbedded With Magnetostrictive Particles

The overall purpose of this research is to characterize the affects of imbedding magnetostrictive particles (MSP) in a CFRP laminate for the purpose of nondestructive evaluation. This paper details an investigation using an analytical and experimental approach. At the time of this publication, both the analytical and experimental investigations are in a preliminary stage and the results have not yet converged. The analytical investigation utilizes fundamental equations for the magnetomechanical properties of the MSP and classical laminate theory for the strength and stiffness of the CFRP laminate to obtain a model of the combination. It is assumed that the magnetomechanical relationship of the MSP layer is a function of the prestress acting on the layer. This relationship is nonlinear in nature but is broken down into a number of linear sections to facilitate analysis. This prestress acting on the MSP layer is a result of the CFRP laminate’s stiffness resisting the induced strain of the MSP layer. Classical laminate theory is used to obtain the value of the prestress as a function of this induced strain. As would be expected, this analysis becomes an iterative process. The induced strain is calculated based on a prestress level of zero. This strain is then used to calculate the amount of stress in the CFRP laminate which becomes the prestress value, and the process is repeated until convergence is reached. Unidirectional CFRP laminates are used in this analysis. The experimental approach involved testing a collection of composite beams imbedded with MSP using a scanner that surrounded the beams. The scanner was composed of an excitation coil and a sensing coil. A detailed schematic of the scanner is included in the paper showing the slide along which the scanner apparatus moved, and the sensing coil surrounded by the excitation coil. The samples used in this analysis were constructed from unidirectional prepreg carbon fiber with varying internal delaminations, ply orientations, and number of plies. A program was constructed that allowed the user to control the signal being output to the excitation coil as well as record data from the sensing coil. The results presented in this paper are not final and will be used to create a foundation for continuation of this research.Copyright

Experimental fabrication and nondestructive testing of carbon fiber beams for delaminations using embedded terfenol-D particles

The experimental results for damage sensing using embedded magnetostrictive particles as sensors in carbon fiber reinforced polymer laminates are presented. Laminates constructed of varying counts of pre-impregnated plies (Hexcel AS4/3501- 6) are embedded with Terfenol-D particles and a delamination to observe changes in the sensing signal in and around the damage region. The testing apparatus consists of a primary circuit to generate a magnetic flux excitation and a secondary circuit to sense voltage induced into a pickup coil. In addition, three groups of test results were generated to observe the effect of fabrication on sensing. The experimental results from the three groups reveal that the particle distribution has a significant effect on the sensing signal. The sensing signal is dominated by changes in local particle distribution and the effect of the delamination and ply variation did not have a discernible effect on the sensing signal for this setup. doi: 10.12783/SHM2015/10

Design and Fabrication of a Functionally Modified Bimorph Actuator

In recent years, the use of microelectromechanical systems (MEMS) devices has led to high performing actuators for various applications, including unmanned air vehicles (UAVs) for defense applications. The incorporation of MEMS technology in this field has resulted in miniaturized UAVs with the capability of carrying out sophisticated reconnaissance and relaying real time information remotely; however, maneuverability of these devices around obstacles is still a challenge. This paper presents the design and fabrication of a functionally modified bimorph actuator with enhanced UAV aerodynamics and maneuverability. The actuator is a metal-based MEMS device consisting of stainless steel, lead zirconate titanate (PZT), and titanium/platinum electrodes. COMSOL analysis was performed to examine optimal device design parameters and is presented in this paper. The design consists of off-axis PZT segments on a bimorph PZT layer which results in bend twist coupling. A detailed description of the fabrication process flow developed based on the optimization of the device design is also given. MEMS processing technology was incorporated to produce a torsional cantilever beam that produces angular and linear displacement for superior UAV maneuverability and its performance is also presented in this paper.Copyright

Special Issue: 2012 ASME Conference on Smart Materials, Adaptive Structures, and Intelligent Systems

The 2012 ASME Conference on Smart Materials, Adaptive Structures, and Intelligent Systems (SMASIS) was held from 19 to 21 September 2012, in Stone Mountain, GA. As in its prior incarnations, the conference was a highly successful and energetic forum in which to develop discussions and collaborations among the conference delegates in adaptive structures, intelligent systems, and structural health monitoring. Participants enjoyed the distinctive atmosphere at a special ‘‘Georgia on my Mind’’ pioneer banquet that was held in the Georgia Aquarium. Conference delegates enjoyed a wonderful dinner, after touring the world’s largest aquarium. With more than 10 million gallons of water, the Georgia Aquarium has more aquatic life than any other aquarium. The six distinct galleries within the Georgia Aquarium depict different aquatic habitats, ranging from arctic to tropical waters, featuring the largest collection of aquatic animals. This was a unique setting for the Pioneer Banquet! Symposium 4: Integrated System Design and Implementation

A study of component surface refurbishment

The act of surface refurbishment of worn components is of itself both environmentally friendly and something which can be accomplished in a timely and convenient manner. It is environmentally friendly since it conserves both material and energy which would be otherwise expended in producing new components. It thus follows that it is also a convenient time-saver. There are many approaches to surface refurbishment, which include Laser Engineered Net Shaping (LENS), and weld repair, to name just two. All are likely to involve machining in the generation of the new surface. It is true to say that, indeed, most metallic surfaces will have experienced some degree of machining. This leads to the possibility that the properties of surfaces generated by machining are likely to be affected by their superficial state of stress and characteristics of the refurbished layer. Therefore our proposed research is in the characterization of the machinability of the remanufactured surface and the subsequent component performance. Such characteristics include fatigue, corrosion and oxidation.