This thesis presents an experimental analysis of the effect of temperature and thermal cycles on the performance of PZT ceramics in fuel injector applications. Due to the increase in the implementation of piezoceramics in applications such as fuel injection technology, it is imperative to understand how temperature affects piezoceramic performance. In this project, the fundamental piezoelectric properties (d_33, ε_33^T, s_33^E) of bulk PZT samples and high electric-field properties of piezoelectric stack actuators were obtained with respect to temperature and thermal cycles. The results show that increasing temperature will increase the fundamental piezoelectric properties of bulk piezoceramics, capacitance of stack actuators, and the displacement of piezoactuators in the absence of external load. Raising the temperature while applying a constant preload will initially increase piezoactuator displacement, but decrease it at higher temperatures. Temperature had a negative effect on the hysteresis in the displacement-voltage. Additionally, thermal hysteresis decreased significantly in subsequent temperature cycles.

This thesis presents an experimental analysis of the effect of temperature and thermal cycles on the performance of PZT ceramics in fuel injector applications. Due to the increase in the implementation of piezoceramics in applications such as fuel injection technology, it is imperative to understand how temperature affects piezoceramic performance. In this project, the fundamental piezoelectric properties (d_33, ε_33^T, s_33^E) of bulk PZT samples and high electric-field properties of piezoelectric stack actuators were obtained with respect to temperature and thermal cycles. The results show that increasing temperature will increase the fundamental piezoelectric properties of bulk piezoceramics, capacitance of stack actuators, and the displacement of piezoactuators in the absence of external load. Raising the temperature while applying a constant preload will initially increase piezoactuator displacement, but decrease it at higher temperatures. Temperature had a negative effect on the hysteresis in the displacement-voltage. Additionally, thermal hysteresis decreased significantly in subsequent temperature cycles.

This study evaluates the application of smart damping materials for reducing structural noise and vibrations. The primary purposes of this study are to: 1. Explore the feasibility of smart damping materials, such as piezoelectric materials, for augmenting and improving the noise and vibration benefits of passive damping materials, and 2. Provide a preliminary evaluation of the noise and vibration benefits, and weight savings of smart damping material as compared to conventional damping treatments. To achieve the objectives of the study, a special test rig, designed to measure both vibrations and structure-borne noise of a test plate, was constructed and validated in the early stages of the study. Upon validating the test rig and the instrumentation that was set up for data collection and processing, a series of tests were performed. The tests were intended to establish a baseline for the test rig and compare the performance of smart damping materials with a number of passive interior automotive treatments. Further, in order to evaluate the effect of smart damping materials on the sound transmission loss, a series of tests were conducted according to the SAE J1400 test specifications. The tests evaluate the transmission loss for smart damping materials for an undamped and a damped plate. The passive damping technique used for this study involved attaching piezoelectric patches with resonant electrical shunts. The vibration modes of the plate were determined both analytically and experimentally, using laser measurement techniques, in order to determine effective placement of the piezoceramic materials. Three piezoceramic patches were applied to control four structural resonance frequencies of the plate. The tests show that smart damping materials have substantial performance benefits in terms of providing effective noise and vibration reduction at a frequency range that is often outside the effective range of passive damping materials. Further, judging by the acceleration and noise reduction per added weight, the test results indicate that smart damping materials can decrease the vibration peak of a steel plate at 151 Hz by up to 16.24 dB with an additional weight of only 0.11 lb. The addition of constrained-layer damping (CLD) can decrease that same peak by 18.65 dB, but it weighs 10 times more. This feature of smart damping materials is particularly useful for solving particular noise or vibration problems at specified frequencies, without adding any weight to the vehicle or changing the vehicle structure. / Master of Science

The characteristics of an automotive passenger seat in response to vibrational excitations are examined and an active vibration isolation system incorporating smart materials is designed, built, and tested. Human sensitivity to vibration is discussed. Characteristics of road roughness are discussed and used to implement a representative test input to a passenger seat system. extsc{Matlab} is used to model the car seat and vehicle system with four degrees of freedom to determine actuator requirements. Selection and implementation of a low--profile, prestressed piezoceramic device into an active seat suspension system is described, and experimental results of the actuator assembly performance are presented. Vibration isolation is realized in an experimental setup representing one quarter of a seat and passenger's total mass, using one actuator assembly (representing one corner of the seat suspension). For an input power spectrum representative of a passenger vehicle environment, the smart material actuator assembly, as applied to a quarter seat experimental setup, is proven to be capable of isolating vibration with an isolation frequency of 2Hz and no resonant peak, versus 6Hz and a resonant peak of 2g/g for an actual passenger seat tested. / Master of Science

A novel segmented electrodes linear ultrasonic motor (USM) was developed. Using a planar vibration mode concept to achieve elliptical motion at the USM drive-tip, an attempt to decouple the components of the drive-tip trajectory was made. The proposed design allows greater control of the drive-tip trajectory without altering the excitation voltage. Finite element analyses were conducted on the proposed design to estimate the performance of the USM. The maximum thrust force and speed are estimated to be 46N and 0.5370m/s, respectively. During experimental investigation, the maximum thrust force and speed observed were 36N and 0.223m/s, respectively, at a preload of 70N. Furthermore, the smallest step achievable was 9nm with an 18μs impulse. Nevertheless, the proposed design allowed the speed of the USM to vary while keeping the thrust force relatively constant and allowed the USM to achieve high resolution without a major sacrifice of thrust force.

A novel segmented electrodes linear ultrasonic motor (USM) was developed. Using a planar vibration mode concept to achieve elliptical motion at the USM drive-tip, an attempt to decouple the components of the drive-tip trajectory was made. The proposed design allows greater control of the drive-tip trajectory without altering the excitation voltage. Finite element analyses were conducted on the proposed design to estimate the performance of the USM. The maximum thrust force and speed are estimated to be 46N and 0.5370m/s, respectively. During experimental investigation, the maximum thrust force and speed observed were 36N and 0.223m/s, respectively, at a preload of 70N. Furthermore, the smallest step achievable was 9nm with an 18μs impulse. Nevertheless, the proposed design allowed the speed of the USM to vary while keeping the thrust force relatively constant and allowed the USM to achieve high resolution without a major sacrifice of thrust force.

Piezoelectrics offer high actuation authority and sensing over a wide range of frequencies. A Macro-Fiber Composite is a type of piezoelectric device that offers structural flexibility and high actuation authority. A challenge with piezoelectric actuators is that they require high voltage input; however the low power consumption allows for relatively lightweight electronic components. Another challenge, for piezoelectric actuated aerodynamic surfaces, is found in operating a relatively compliant, thin structure (desirable for piezoceramic actuators) in situations where there are relatively high external (aerodynamic) forces. Establishing an aeroelastic configuration that is stiff enough to prevent flutter and divergence, but compliant enough to allow the range of available motion is the central challenge in developing a piezocomposite airfoil. The research proposed here is to analyze and implement novel electronic circuits and structural concepts that address these two challenges. Here, a detailed theoretical and experimental analysis of the aerodynamic and electromechanical systems that are necessary for a practical implementation of a piezocomposite airfoil is presented. First, the electromechanical response of Macro-Fiber Composite based unimorph and bimorph structures is analyzed. A distributed parameter electromechanical model is presented for interdigitated piezocomposite unimorph actuators. Necessary structural features that result in large electrically induced deformations are identified theoretically and verified experimentally. A novel, lightweight electrical circuitry is proposed and implemented to enable the peak-to-peak actuation of Macro-Fiber Composite bimorph devices with asymmetric voltage range. Next, two novel concepts of supporting the piezoelectric material are proposed to form two types of variable-camber aerodynamic surfaces. The first concept, a simply-supported thin bimorph airfoil, can take advantage of aerodynamic loads to reduce control input moments and increase control effectiveness. The structural boundary conditions of the design are optimized by solving a coupled fluid-structure interaction problem by using a structural finite element method and a panel method based on the potential flow theory for fluids. The second concept is a variable-camber thick airfoil with two cascading bimorphs and a compliant box mechanism. Using the structural and aerodynamic theoretical analysis, both variable-camber airfoil concepts are fabricated and successfully implemented on an experimental ducted-fan vehicle. A custom, fully automated low-speed wind tunnel and a load balance is designed and fabricated for experimental validation. The airfoils are evaluated in the wind tunnel for their two-dimensional lift and drag coefficients at low Reynolds number flow. The effects of piezoelectric hysteresis are identified. In addition to the shape control application, low Reynolds number flow control is examined using the cascading bimorph variable-camber airfoil. Unimorph type actuators are proposed for flow control in two unique concepts. Several electromechanical excitation modes are identified that result in the delay of laminar separation bubble and improvement of lift. Periodic excitation to the flow near the leading edge of the airfoil is used as the flow control method. The effects of amplitude, frequency and spanwise distribution of excitation are determined experimentally using the wind tunnel setup. Finally, the effects of piezoelectric hysteresis nonlinearity are identified for Macro-Fiber Composite bimorphs. The hysteresis is modeled for open-loop response using a phenomenological classical Preisach model. The classical Preisach model is capable of predicting the hysteresis observed in 1) two cantilevered bimorph beams, 2) the simply-supported thin airfoil, and 3) the cascading bimorph thick airfoil. / Ph. D.

The predictive design of fuel injection hardware used for active combustion control is not well established in the gas turbine industry. The primary reason for this is that the underlying mechanisms governing the flow rate authority downstream of the nozzle are not well understood. A detailed investigation of two liquid fuel flow modulation configurations is performed in this thesis: a piston and a throttle-valve configuration. The two systems were successfully built with piezoelectric actuation to drive the prime movers proportionally up to 800 Hz. Discussed in this thesis are the important constituents of the fuel injection system that affect heat release authority: the method of fuel modulation, uncoupled dynamics of several components, and the compressibility of air trapped in the fuel line. Additionally, a novel technique to model these systems by way of one-dimensional, linear transmission line acoustic models was developed to successfully characterize the principle of operation of the two systems. Through these models, insight was gained on the modes through which modulation authority was dissipated and on methods through which successful amplitude scaling would be possible. At high amplitudes, it was found that the models were able to successfully predict the actual performance reasonably well for the piston device. A proportional phase shifting controller was used to test the authority on a 40-kW rig with natural longitudinal modes. Results show that, under limited operating conditions, the sound pressure level at the limit cycle frequency was reduced by about 26 dB and the broadband energy was reduced by 23 dB. Attenuation of the fuel pulse at several combustor settings was due to fluctuating vorticity and temporal droplet distribution effects. / Master of Science

Methods for comprehensive structural dynamic analysis generally employ input-output modal analysis with a mathematical model of structural vibration using excitation and response data. Recently operational modal analysis methods using only vibration response data have been developed. In this thesis, both input-output and operational modal analysis, in the presence of significant unmeasured excitations, is considered. This situation arises when a test structure cannot be effectively isolated from ambient excitations or where the operating environment imposes dynamically-important boundary conditions. The limitations of existing deterministic frequency-domain methods are assessed. A novel time-domain estimation algorithm, based on the estimation of a discrete-time autoregressive moving average with exogenous excitation (ARMAX) model, is proposed. It includes a stochastic component to explicitly account for unmeasured excitations and measurement noise. A criterion, based on the sign of modal damping, is incorporated to distinguish vibration modes from spurious modes due to unmeasured excitations and measurement noise, and to identify the most complete set of modal parameters from a group of estimated models. Numerical tests demonstrate that the proposed algorithm effectively identifies vibration modes even with significant unmeasured random and periodic excitations. Random noise is superimposed on response measurements in all tests. Simulated systems with low modal damping, closely spaced modes and high modal damping are considered independently. The accuracy of estimated modal parameters is good except for degreesof- freedom with a low response level but this could be overcome by appropriate placement of excitation and response measurement points. These observations are reflected in experimental tests that include unmeasured periodic excitations over 200% the level of measured excitations, unmeasured random excitations at 90% the level of measured excitations, and the superposition of periodic and random unmeasured excitations. Results indicate advantages of the proposed algorithm over a deterministic frequency domain algorithm. Piezoceramic plates are used for structural excitation in one experimental case and the limitations of distributed excitation for broadband analysis are observed and characterised in terms of actuator geometry and modal deformation. The ARMAX algorithm is extended for use with response measurements exclusively. Numerical and experimental tests demonstrate its performance using time series data and correlation functions calculated from response measurements.

The early detection of damage of in-service structural or mechanical systems is of vital importance. With early detection, the damage may be repaired before the integrity of the system is jeopardized, avoiding possible monetary losses, environmental impacts, injury and death. With this goal in mind, many structural health monitoring techniques have been developed which use a combination of sensors and algorithms to collect, process and interpret data to detect damage in a structure. This thesis presents work completed in support of the experimental validation of a novel structural health monitoring technique developed with the aim of providing improved qualitative results compared to those methods currently available.