Table of contents

Economic and reliable online health monitoring strategies are very essential for safe operation of civil, mechanical and aerospace structures. This study presents online structural health monitoring (SHM) techniques using wireless impedance sensor nodes equipped with both functions of structural damage identification and sensor self-diagnosis. The wireless impedance sensor node incorporating a miniaturized impedance measuring chip, a microcontroller and radio-frequency (RF) telemetry is equipped with the capabilities for temperature sensing, multiplexing of several sensors, and local data analysis. The feasibility of the sensor node for structural damage identification is firstly investigated through a series of experimental studies inspecting loosened bolt damage and cut damage cases. Additionally, a temperature effects-free sensor self-diagnosis algorithm is embedded into the sensor node and its feasibility is examined from the experiments monitoring the integrity of each piezoelectric sensor on a wireless sensor network.

Samarium calcium perovskite manganite Sm_0.65Ca_0.35MnO₃ was dispersed homogeneously in a solution of poly(styrene-co-acrylonitrile). A thin film was deposited on (100) oriented silicon substrate by spin-coating and the optical thermochromic behaviour in the infrared range was studied. In the wavelength range 8–14 µm, the optical transmittance of the thermochromic composite coating exhibited a large variation between 173 and 343 K due to a semiconductor–metal first-order transition at T_c = 250 K. The thermochromic behaviour of the composite coatings was optimized. The contrast in the transmittance first increased with pigment content, then reached a maximum value.

The aim of the present study is to investigate the local strain band behavior in conjunction with the texture of NiTi thin sheets under mechanical loading. Firstly, we evaluate the transformation temperature by differential scanning calorimetry (DSC) and the internal structure by transmission electron microscopy (TEM) for NiTi thin sheets. Next, we investigate the texture by the x-ray diffraction method for two NiTi thin sheets with different textures. Then, we measure the local strain distribution arising in NiTi thin sheets under uniaxial tensile loading. Finally, we discuss the 'mechanism of angle, nucleation and propagation for local strain band' and the 'relationship between the macroscopic stress–strain curve and local strain band behavior' on the basis of results in the present study.

In modern cities, many important pipelines are laid underground. In order to prevent these lifeline infrastructures from accidental damage, monitoring systems are becoming indispensable. Third party activities were shown by recent reports to be a major cause of pipeline damage. Potential damage threat to the pipeline can be identified by detecting dangerous construction equipment nearby by studying the surrounding noise. Sound recognition technologies are used to identify them by their sounds, which can easily be captured by small sensors deployed along the pipelines. Pattern classification methods based on principal component analysis (PCA) were used to recognize the sounds from road cutters. In this paper, a Mel residual, i.e. the PCA residual in the Mel scale, is proposed to be the recognition feature. Determining if a captured sound belongs to a road cutter only requires checking how large its Mel residual is. Experiments were conducted and results showed that the proposed Mel-residual-based PCA recognition worked very well. The proposed Mel PCA residual recognition method will be very useful for pipeline monitoring systems to prevent accidental breakage and to ensure the safety of underground lifeline infrastructures.

The mechanical stretching effect on the actuating performance of electroactive cellulose paper (EAPap) was studied. A lattice elongation of cellulose fibrils due to in-plane tensile stress along the stretching direction was observed by the x-ray diffraction method. The shrinkage of the fibril diameter as a function of stretching ratio was confirmed by surface and cross-sectional images. While the actuator performance in terms of bending displacement decreased as the stretching ratio increased, the resonance frequency linearly increased as the stretching ratio increased, which was compared with the theoretical frequency data found from a cantilever beam model. The actuator efficiency was evaluated from the electrical input power consumption and the mechanical output power of an EAPap actuator. It was revealed that the stretching process increased the electro-mechanical efficiency of the EAPap actuator. The mechanism of the influence of the stretching effect on the performance of an EAPap actuator is discussed.

This paper presents a solution to the problem of cable vibration mitigation using a semi-active damping device. The optimal control of such a device is investigated with an evolutionary algorithm. A fitness function for the algorithm is defined, as the total energy removed from the cable by the damper in a numerical simulation. The initial and end conditions of the optimization are defined such that the solution is optimal for a single mode of vibration. The solution produced by the evolutionary algorithm is shown to outperform other popular semi-active control strategies for the given conditions, removing as much as 2.0 and 1.2 times more energy than the optimal linear viscous damper and clipped linear quadratic regulator controller, respectively. It is furthermore shown that the solution can be given as a simple control law parametrized with a single parameter. The performance of the control law derived is assessed by means of numerical simulation with a free vibration decay test. Due to the multiple modes of vibrations induced by the nonlinear damper in this test, the control law performance is slightly decreased compared to the aforementioned efficiency.

This paper proposes a new two-dimensional (2D) actuation method for a microrobot that uses a stationary two-pair coil system. The coil system actuates the microrobot by controlling the magnitude and direction of the external magnetic flux. The actuation of the microrobot consists of an alignment to the desired direction and a linear movement of the microrobot by non-contact electromagnetic actuation. Firstly, the actuation mechanism of the stationary coil system is theoretically derived and analyzed. Secondly, the tendency of the magnetic flux in the coil system are analyzed and compared by preliminary theoretical analysis. Through various locomotive experiments of the microrobot, the performance of the electromagnetic actuation by the proposed stationary two-pair coil system is evaluated. Using the proposed 2D actuation method, the microrobot is aligned to the desired direction by Helmholtz coils and is driven to the aligned direction by Maxwell coils. By the successive current control of the coil system, the microrobot can move along a desired path, such as a rectangular-shaped or a diamond-shaped path.

Ionic polymer–metal composites (IPMCs) form an important category of electroactive polymers and have many potential applications in biomedical, robotic and micro/nanomanipulation systems. In this paper, a nonlinear, control-oriented model is proposed for IPMC actuators. A key component in the proposed model is the nonlinear capacitance of the IPMC. A nonlinear partial differential equation (PDE), which can capture the fundamental physics in the IPMC, is fully considered in the derivation of nonlinear capacitance. A systems perspective is taken to get the nonlinear mapping from the voltage to the induced charge by analytically solving the nonlinear PDE at the steady state when a step voltage is applied. The nonlinear capacitance is incorporated into a circuit model, which includes additionally the pseudocapacitance due to the electrochemical adsorption process, the ion diffusion resistance, and the nonlinear DC resistance of the polymer, to capture electrical dynamics of the IPMC. With electromechanical coupling, the curvature output is derived based on the circuit model. The proposed model is formulated in the state space, which will be the starting point for nonlinear controller design. Experimental verification shows that the proposed model can capture the major nonlinearities in the electrical response of the IPMC.

In this study, a TiNi/Al6061 shape memory alloy (SMA) composite was fabricated by the hot press method, and pressed by a roller for its strength improvement using the shape memory fiber shrinkage phenomenon. These two kinds of specimens were fabricated with 0% and 5% volume ratio and 0%, 10 % and 20% reduction ratio of TiNi alloy fiber, respectively. A fatigue test has been performed to evaluate the fatigue life for the fabricated TiNi/Al SMA composite as an S–N curve. The results from the Goodman diagram is able to illustrate the failure criterion and fatigue limit between tensile and bending fatigue strength in the fatigue characterization of TiNi/Al SMA composites.

This paper studies the piezoresistive property of the CNT/cement composite to explore its feasibility as an embedded stress sensor for civil structures such as roadways, levees and bridges. The experimental results show that the electrical resistance of the CNT/cement composite changes with the compressive stress level, indicating the potential of using the CNT/cement composite as a stress sensor for civil structures. The piezoresistive responses of the composite with different fabrication methods and CNT doping levels were also studied. It is found that dispersion-assistant surfactants could block the contacts among carbon nanotubes, thus impairing the piezoresistive response of the composite, while a higher CNT doping level could improve the sensitivity of the composite stress response.

In this paper two nonlinear model based control algorithms have been developed to monitor the magnetorheological (MR) damper voltage. The main advantage of the proposed algorithms is that it is possible to directly monitor the voltage required to control the structural vibration considering the effect of the supplied and commanded voltage dynamics of the damper. The efficiency of the proposed techniques has been shown and compared taking an example of a base isolated three-storey building under a set of seismic excitations. Comparison of the performances with a fuzzy based intelligent control algorithm and a widely used clipped optimal strategy has also been shown.

This paper presents analytical models for studying the transient behavior of several power harvesting circuit topologies for use with piezoelectric bending transducers. Specifically, the problem of charging a large storage capacitor, which is inherently a time-varying process, is considered. Three circuit designs are studied—direct charging, synchronized switching and discharging to a storage capacitor, and synchronized switching and discharging to a storage capacitor through an inductor (SSDCI)—and they are compared to a matched resistive load case. Analytical models are developed for these cases to predict the charging rates and output power for various values of storage capacitance and quality factor. Experimental circuit designs are given and their results are compared to the theoretical predictions. It is shown that these predictions are accurate when the losses in the circuit are considered in the model. In spite of these losses, it is demonstrated that the SSDCI design can produce about 200% the output power of the idealized, matched resistive load case throughout the charging process and substantially reduce the charging time of the storage capacitor.

A dynamic model for the electric field-dependent steady-state vibrational response of a rectangular sandwich plate with a tunable electrorheological fluid (ERF) interlayer, subjected to a general harmonic transverse excitation, is developed. Hamilton's principle and the classical thin plate theory are applied to derive a set of fully coupled dynamic equations of motion along with the associated general boundary conditions. Assuming simply-supported edge conditions, the displacement components of the ERF-based sandwich plate are postulated by means of generalized double Fourier series with frequency-dependent coefficients. The natural frequencies and modal loss factors are subsequently determined by solving a complex eigenvalue problem. Analytical solutions are also obtained for the forced vibration characteristics of the adaptive structure under different external transverse excitations of varying frequency (0–300 Hz) and applied electric field strength (0–3.5 kV mm⁻¹). Primary attention is focused on the effects of electric field magnitude, geometric aspect ratio, loading type, and ER core layer thickness on the dynamic characteristics of the sandwich plate. In addition, an effort is made to find the optimal electric field which yields minimized vibration amplitude for each excitation frequency. Limiting cases are considered and good agreements with the numerical solutions available in the literature are obtained.

The use of composite materials in marine, aerospace and automotive applications is increasing; however, several kinds of damages of composite materials may influence its durability and future applications. In this paper, a methodology was presented for damage detection of laminated composite plates using dielectrometry sensors. The presence of damage in the laminated composite plate leads to changes in its dielectric characteristics, causing variation in the measured capacitance by the sensors. An analytical model was used to analyse the influence of different sensor parameters on the output signals and to optimize sensor design. Two-dimensional finite element (FE) simulations were performed to assess the validity of the analytical results and to evaluate other sensor design-related parameters. To experimentally verify the model, the dielectric permittivity of the composite plate was measured. In addition, a glass fibre reinforced polymer (GFRP) laminated plate containing pre-fabricated slots through its thickness to simulate delamination and water intrusion defects was inspected in a laboratory setting. Excellent agreements were found between the experimental capacitance response signals and those predicated from the FE simulations. This cost-effective technique can be used for rapid damage screening, regular scheduled inspection, or as a permanent sensor network within the composite system.

This research presents an exact solution of finitely long, simply supported, orthotropic, functionally graded piezoelectric (FGP), cylindrical shell panels under pressure and electrostatic excitation. The FGP cylindrical panel is first divided into linearly inhomogeneous elements (LIEs). The general solution of governing partial differential equations of the LIEs is obtained by separation of variables. The highly coupled partial differential equations are reduced to ordinary differential equations with variable coefficients by means of appropriate trigonometric expansion of displacements and electric potential in circumferential and axial directions. The resulting governing ordinary differential equations are solved by the Galerkin finite element method. In this procedure the quadratic shape function is used in each element. The present method is applied to several benchmark problems. The coupled electromechanical effect on the structural behavior of functionally graded piezoelectric cylindrical shell panels is evaluated. The influence of the material property gradient index on the variables of electric and mechanical fields is studied. Finally some results are compared with published results.

In this study, dynamic modeling of an electrorheological (ER) damper is performed considering the unsteady behaviors of ER fluid flow through the annular duct of the damper. After describing the configuration of the ER damper, quasi-static modeling of the damper is conducted on the basis of the Bingham model of ER fluid. The pressure drop of the unsteady ER fluid flow through the annular duct between the electrodes of the damper with a known variation of flow rate is then obtained by solving the momentum equation of the ER fluid flow using the Laplace transform technique. Based on the proposed unsteady flow solution, the simulated results are obtained and compared with measured ones in order to evaluate the effectiveness of the proposed model. In addition, in order to reduce the computation load, a simplified solution of the dynamic damping force is proposed with validation.

A great amount of research has been done to develop piezoelectric material-based energy harvesting devices as power generators for a variety of portable and low power consuming devices. Among the possibilities for energy harvesters, the 31 type cantilever piezoelectric benders have generally been used. In this work a unimorph piezoelectric cantilever beam with an interdigitated electrode pattern was examined. The focus of this paper is to develop a model and propose design parameters to improve the energy generating performance of the interdigitated piezoelectric energy harvester.