As mechanisms approach the micro scale, manufacture and assembly of linear coil springs becomes nearly impossible. For this reason, compliant functionally binary pinned-pinned segments are frequently used in place of them. A new pseudo-rigid-body model (PRBM) is presented for circular functionally binary pinned-pinned (FBPP) segments that undergo large, nonlinear deflections for both tension and compression. A new method of evaluating the maximum moment in the beam is presented, called the focal moment method , which significantly increases the accuracy of the force for a given displacement. This paper also shows how some FBPP segments can be modeled as simple linear tension/compression springs. The deflection limits for a given maximum error can be determined analytically, thereby making it possible to use optimization algorithms in the design of these springs. The effect of the size of the rigid pin joints is also discussed.

Self-actuating aircraft wings for in-flight deicing with minimal power requirements are proposed. Lightweight piezoelectric actuators are utilized to excite the wing structure to its natural frequencies to induce shear stresses on the surface of the wing. The shears are generated in such a way that they are sufficient to break the weak bond between the ice layer and the wing surface. A laminated composite cantilever plate is used for the modeling and analysis. Analytical model is developed to predict the natural frequencies and shear stresses on the surface of the plate and finite element modal analysis is carried out to verify the results. In addition, finite element model involving the ice deposited on the underlying structure is built. The dynamic responses of the structure to harmonic excitation to its first five natural frequencies are investigated. It is observed that significant amount of ice de-bonding from the substrate occurs in the third mode, or the second symmetric mode. Moreover, the energy requirements of the piezoelectric actuators to actuate an adaptive composite structure with given weight are evaluated.

In this paper, the vibration behavior and control of a clamped-free rotating flexible cantilever arm with fully covered Active Constrained Layer Damping (ACLD) treatment is investigated. The arm is rotating in a horizontal plane in which the gravitational effect and rotary inertia are neglected. The stress-strain relationship for the viscoelastic material (VEM) is described by a complex shear modulus while the shear deformations in the two piezoelectric layers are neglected. Hamilton’s principle in conjunction with finite element method (FEM) is used to derive the nonlinear coupled differential equations of motion and the associated boundary conditions that describe the rigid hub angle rotation, the arm transverse displacement and the axial deformations of the three-layer composite. This refined model takes into account the effects of centrifugal stiffening due to the rotation of the beam and the potential energies of the VEM due to extension and bending. Active controllers are designed with PD for the piezo-sensor and actuator. The vibration frequencies and damping factors of the closed-loop beam/ACLD system are obtained after solving the characteristic complex eigenvalue problem numerically. The effects of different rotating speed, thickness ratio and loss factor of the VEM as well as different controller gain on the damped frequency and damping ratio are presented. The results of this study will be useful in the design of adaptive and smart structures for vibration suppression and control in rotating structures such as rotorcraft blades or robotic arms.

A technique for a non-destructive detection, location and severity determination of structural defects by means of a time domain technique is presented. Since damage in a structure causes changes in the physical coefficients of elastic modulus and damping parameters, the response of an undamaged and a damaged structure to the same input excitation is different, and this can be used in a damage identification strategy. The present work uses a continuous damage model to describe the current integrity state of a structure. In order to determine this state of structural damage the minimization of an error function is desired, such a function is basically the difference between the time response of the structural model and the real structure one to the same input excitation. The effectiveness of the proposed technique is assessed on a beam like structure, where displacements, accelerations or strains may considered as being measured at a subset of the system degrees of freedom. In order to furnish realism to performed simulations, the corrupting effects of signal filtering and sampling are considered. The analysis of the results for different levels of signal-to-noise ratio is also carried on.

The EM method is a valuable tool for Civil Engineering for estimation of the real stress in the prestressing tendons, quality control during construction period, calculating the stress loss due to friction and relaxation, long-time monitoring of stress changes due to concrete creep, temperature changes, traffic load etc. Overview of EM technique with practical applications in the Civil Engineering is presented. The new generation of EM measuring devices is based on more than 15 years experience, including health monitoring systems for the nuclear power plant and a large span cable stayed and suspension bridges. Examples of laboratory and field tests are presented, including uncertainty of stress measurement, long-time stability, resolution and reliability.

Ionic Polymer-Metal Composite (IPMC) is a new class of polymeric material exhibiting large strain with inherent soft actuation. The observed motion characteristics of an IPMC subjected to an electric field is highly non-linear. This is believed to be due primarily to the particle electrodes on the IPMC surface, which is inherently both capacitive and resistive due to particle separation and density. Knowing that the value of resistivity and capacity can be manipulated by the number of metal platings applied to the IPMC, the force response of an IPMC when subjected to an imposed electric field is due to the interaction of an array of capacitors and resistors along with ionic migration. In this effort we attempt to incorporate a capacitive and resistive model into the previously developed linear irreversible thermodynamic model. The advantages of using such a model are i) the possible dynamic predictability of the material itself; and ii) the realization of capacitive and resistive effect arising from the particle electrodes and the base polymer, respectively. The behavior of the proposed model can explain typical experimentally obtained values well. Also, an experimental effort to improve the properties of the base polymer was carried out by a novel nanocomposite technique. The experiment results on the current/voltage (I/V) curves indicate that the starting material of ionic polymer-metal composites (IPMCs) can be optimized to create effective polymer actuators.

Inflated space-based structures have become popular over the past three decades due to their minimal launch-mass and launch-volume. Once inflated, these space structures are subject to vibrations induced by guidance systems and space debris as well as from variable amounts of direct sunlight. Understanding the dynamic behavior of space-based structures is critical to ensuring their desired performance. Inflated materials, however, pose special problems when testing and trying to control their vibrations because of their lightweight, flexibility, and high damping. Traditional modal testing techniques, based on single-input, single-output (SISO) methods, are limited for a variety of reasons when compared to their multiple counterparts. More specifically, SISO modal testing techniques are unable to reliably distinguish between pairs of modes that are inherent to axi-symmetric structures (such as an inflated torus, a critical component of a gossamer spacecraft). Furthermore, it is questionable as to whether a single actuator could reliably excite the global modes of a true gossamer craft, such as a 25 m diameter torus. In this study, we demonstrate the feasibility of using a multiple-input multiple-output (MIMO) modal testing technique on an inflated torus. In particular, the refined modal testing methodology focuses on using Macro-Fiber Composite (MFC ® ) patches (from NASA Langley Research Center) as both actuators and sensors. MFC ® patches can be integrated in an unobtrusive way into the skin of the torus, and can be used to find a gossamer structure’s modal parameters. Furthermore, MFC ® excitation produces less interference with suspension modes of the free-free torus than excitations from a conventional shaker. The use of multiple actuators is shown to properly excite the global modes of the structure and distinguish between pairs of modes at nearly identical resonant frequencies. Formulation of the MIMO test as well as the required postprocessing techniques are explained and successfully applied to an inflated Kapton ® torus.

A topology optimization method is developed to design a piezoelectric ceramic actuator together with a compliant mechanism coupling structure for dynamic applications. The objective is to maximize the mechanical efficiency with a constraint on the capacitance of the piezoceramic actuator. Examples are presented to demonstrate the effect of considering dynamic behavior compared to static behavior, and the effect of sizing the piezoceramic actuator on the optimal topology and the capacitance of the actuator element. Comparison studies are also presented to illustrate the effect of damping, external spring stiffness, and driving frequency. The optimal topology of the compliant mechanism is shown to be dependent on the driving frequency, the external spring stiffness, and if the piezoelectric actuator element is considered as design or non-design. At high driving frequencies, it was found that the dynamically optimized structure is very near resonance.

Shallow paraboloidal shells of revolution are common components for reflectors, mirrors, etc. This study is to investigate the micro-control actions and distributed control effectiveness of precision paraboloidal shell structures laminated with segmented actuator patches. Mathematical models and governing equations of the paraboloidal shells laminated with distributed actuator layers segmented into patches are presented first, followed by formulations of distributed control forces and micro-control actions including meridional/circumferential membrane and bending control components based on an assumed mode shape function and the Taylor series expansion. Distributed control forces, patch sizes, actuator locations, micro-control actions, and normalized control authorities of a shallow paraboloidal shell are then analyzed in a case study. Analysis indicates that 1) the control forces and membrane/bending components are mode and location dependent, 2) the meridional/circumferential membrane control actions dominate the overall control effect, 3) there are optimal actuator locations resulting in the maximal control effects at the minimal control cost for each natural mode. The analytical results provide generic design guidelines for actuator placement on precision shallow paraboloidal shell structures.

An optimization method has been developed for the design of a smart conformable rotor airfoil with distributed piezoelectric actuators. A conformable airfoil is proposed as a substitute for trailing edge flaps used for helicopter vibration reduction by achieving high frequency camber variations. A topology optimization approach is used where the objective is to maximize trailing edge deflection while minimizing airfoil deformations due to aerodynamic loads. Solutions of the design problem are obtained using Sequential Linear Programming coupled with a Finite Element Analysis procedure. Results show good algorithm convergence and satisfactory airfoil deformations. A study of the effects of different active material resources, skin thickness and aerodynamic loads is performed. Changes in lift coefficient are found to be lower than those obtained for an equivalent flap at similar deflection angles, suggesting that larger deflections might be required for vibration reduction purposes.

Ongoing research is presented on processing of NiTi-based shape memory alloy (SMA) foams. The aim is to demonstrate a new class of materials that combine the advantages of light-weight metallic foams with the strain recovery and energy-dissipation capability of SMAs. There are a number of potential novel structural and biomedical applications that could be enabled by the unusual passive and active properties of such a material. This paper presents initial results on our attempt to fabricate functional prototype specimens using a polymeric foam precursor and a powder metallurgy process to produce NiTi foams with user-selected topology and relative density. It is shown that open-cell NiTi foams with relative density less than 5% can be produced with this technique. While definite martensitic transformational behavior has been achieved in the prototypes, the quality of the foams are found to be sensitive to the sintering temperature, the binder system employed, and the levels of interstitial contamination. Further work is needed before good superelastic and shape-memory properties can be demonstrated. Nevertheless, the current technique appears promising, since the method is capable of producing NiTi foam with a more regular structure and at a relative density nearly an order of magnitude less than other techniques currently used to produce porous NiTi.

This paper describes an INertially STabilized Rifle where a Recurve actuator, constructed from piezoelectric material, is used to internially stabilize the barrel assembly of a tactical rifle to compensate for the small user-induced disturbances. The requirements of this system are discussed and the actuator requirements are derived. A prototype Recurve actuator is described and the test results reported. Similarly, the power electronics needed for INSTAR are discussed. Test results for an prototype circuit are given.

Embedded-Ultrasonics Structural Radar (EUSR) is a new concept and methodology for in-situ nondestructive evaluation (NDE) of thin-wall structures. EUSR utilizes (a) a Piezo Wafer Active Sensors (PWAS) array embedded onto the structure; and (b) electronic modules for signal transmission/reception, processing, and interpretation. The EUSR methodology is developed as an extension of our previous work on the Lamb wave propagation NDE. Based on the study of the Lamb wave characteristic, the excitation signal is optimized to obtain good signal to noise ratio. Lamb wave speed-frequency curve is plotted to obtain the wave speed of the excitation signal. This wave speed is then used to map the EUSR data from time domain to distance domain, thus the locations of the reflectors can be visually displayed. The EUSR algorithm is adopted from the beamforming process currently used in phased-array radar applications. Each element in the PWAS array plays the role of both transmitter and receiver. A circuit is designed to change the role of the PWAS in a round robin fashion. The responses of the structure to all the excitation signals are collected. By applying the EUSR algorithm, an appropriate delay is applied to each signal in the data set to make them all focus on a direction denoted by angle φ . When this angle φ is changed from 0 to 180 degrees, a virtual scanning beam is formed and a large area of the structure can be interrogated. The EUSR algorithm is explained in this paper. Experimental results from a proof-of-concept EUSR system are also presented.

This paper introduces a new configuration of a Continuously Variable Transmission (CVT) that is self-adjusting and designed as a compliant mechanism. This new configuration is called the Pivot-Arm CVT. The criteria for classification as a Pivot-Arm CVT is discussed. An analytical model describing the performance of the Pivot-Arm CVT is developed. Special design considerations which may be useful in implementing Pivot-Arm CVTs are introduced and explained. The Pivot-Arm CVT model is validated through controlled testing of two Pivot-Arm CVT prototypes.

Scientists have used internal variables to model time-dependent material behavior for many years. Since the 1980s they have been employed to predict transient response of structures that include viscoelastic materials. The potentially large number of extra states introduced by the internal variables can be problematic when designing control systems, so the purpose of this paper is to explore how internal variables affect control system design. Practical designs are based on output feedback of a limited number of the physical states, but this brings up the question of whether it is advantageous to recreate the full state vector (including internal states) using a standard observer. Internal variables based on Maxwell models are used to address observability and controllability as well as full- and partial-state feedback on a single-degree-of-freedom system. Comparisons are also made between complex-modulus and internal-variable representations of viscoelastic behavior.

Structures and industrial equipment often operate in environments where temperature variations take place. Although thermal effects may be negligible in some cases, they have caused the unexpected failure of mechanical systems many times. Whether or not temperature has significant effects on the dynamical behavior of such machines and structures depends upon several aspects, amongst which are geometry, material properties and boundary conditions. In this paper we investigate the dynamical behavior of a clamped beam under the influence of a uniform, quasi-statically varying temperature field. An analytical model was used, based on Euler-Bernoulli’s beam theory with the introduction of the proper boundary conditions. Temperature effects are included in terms of an axial force that shows up when the beam tends to thermally expand, but this expansion is restrained by the clamping. Preliminary results do not agree with experimental data, since perfect clamping is difficult to achieve in practice. Finally the model is updated with the inclusion of axial and torsional springs connecting the beam to the support. The spring constants were calculated through optimization procedure to minimize the differences between the natural frequencies obtained from the analytical model and the corresponding experimental ones. Agreement with experimental results is reasonable up to the 4th mode of the beam. In the future, this analytical model is to be used for design and simulation of an active controller that accounts for temperature changes in the structure.

Small scale probes implementing shape memory alloy (SMA) actuation show great promise in applications requiring remote and minimally invasive access to small environments. Such environments include physiological spaces like those located in human and animal bodies as well as cavities within mechanical systems. Probes examined here are generally snake like in appearance composed of one or multiple independent segments, which in turn are made up of one or multiple SMA actuators performing work against an elastic spine. As the actuator(s) of a given segment are activated, the spine bends causing the probe to bend in the area of that segment. When the actuator(s) are deactivated, the force generated in the bending of the spine returns the segment to its neutral position. Activation and deactivation of actuators is accomplished by heating and cooling respectively, enacting the solid phase changes that are characteristic to the shape memory effect. The gage of control over probe shape depends on the number of independent segments that are available per unit length and the degree of control an operator has over each of the segments. The work presented here discusses the constraints imposed on the design of SMA actuated probes, and how those constraints become more critical and limiting with reduced physical scale and refinement of motion control. Numerical and finite element models have been developed showing the interrelationship between mechanical design, the thermal and phase states of the SMA actuator(s), and the mechanical performance of the total system. Performance concerns examined include probe shape control and the limits of shape change as a function of physical scale. Comparative data is presented between behavior predicted by the models developed and performance observed during the testing of prototypes. It is concluded that segment length, linked to refinement of probe control, is limited by its thermal boundary conditions.

The last decade has seen the advent of active aperture antennas and other large distributed parameter systems. These antennas have the capability to change their shape to resemble a desired radiation pattern. In this study a method to simultaneously achieve active shape and vibration control of distributed parameter systems is presented. The optimal actuator location is computed for a desired profile using non-linear optimal programming techniques. For most shape control applications the actuator and sensor dynamics are much faster than the structural dynamics and slow shape changes are sufficient, thus quasi-static analysis is sufficient. The quasi-static actuation forces for the desired profile are then calculated by using independent modal space control (IMSC) principles. Quasi-static shape control is then implemented in a closed loop control using a 3-D photogrammetry sensing system. A sliding mode controller is designed for each dominant mode such that it drives the error between the required and actual modal contribution to zero. Conventional sliding mode controllers are discontinuous in nature and they might cause “control spillover”. This is avoided by using an “observer-based” solution.

A general-order perturbation method involving multiple perturbation parameters is developed for eigenvalue problems with changes in the stiffness parameters. The perturbation solutions and eigenparameter sensitivities of all orders are derived explicitly. The perturbation method is used iteratively in conjunction with an optimization method in a robust damage detection algorithm. The generalized inverse method is used efficiently with the first order perturbations, and the gradient and quasi-Newton methods are used with the higher-order perturbations. Numerical simulations demonstrated the effectiveness of the algorithm in detecting the locations and extents of small to large levels of damage.

The aim of this research is to determine the optimal shape of a constrained viscoelastic damping layer on an elastic beam by means of topology optimization. The optimization objective is to maximize the system loss factor for the first resonance frequency of the base beam. All previous optimal design studies on viscoelastic lamina have been size or shape optimization studies, assuming a certain topology for the damping treatment. In this study, this assumption is relaxed, allowing an optimal topology to emerge. The loss factor is computed using the Modal Strain Energy method in the optimization process. Loss factor results are validated by using the half-power bandwidth method, which requires obtaining the forced response of the structure. The ABAQUS finite element code is used to model the structure with two-dimensional continuum elements. The optimization code uses a Sequential Quadratic Programming algorithm. Results show that significant improvements in damping performance, on the order of 100% to 300%, are obtained by optimizing the constrained damping layer topology. A novel topology for the constraining layer emerges through the optimization process.