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Volume 28
Number 5, May 2019
Buy this issue in printTopical Review
A review of manufacturing techniques of smart composite structures with embedded bulk piezoelectric transducersSince the mid-1980's, sensors and actuators have been combined with composite materials in order to enhance and increase the functionalities of the resulting products. These innovative devices are called intelligent, adaptive or smart structures. Their main applications are related but not limited to vibration control, structural health monitoring, shape control and energy harvesting. One possible way of developing these devices is to embed the smart materials inside the structure. In this case, the main challenge is the way of embedding the smart material during the manufacturing process. This review presents the key elements of the manufacturing process, provides an overview of the techniques developed to embed the bulk piezoelectric transducers in the composite and details the achievements made with them. In conclusion, some guidelines for futures researches and developments are proposed
Focus Papers
Response time effect of magnetorheological dampers in a semi-active vehicle suspension system: performance assessment with quantitative feedback theoryThis paper presents vibration control performances of a semi-active full-car suspension system with very-fast response magneto-rheological (MR) dampers. In this study, MR damper dynamics is captured by the first order model which is realistic, efficient and simple form. As a first step, the response time of the proposed MR damper and one of commercial MR dampers is experimentally identified as around 7 ms and 26 ms, respectively. The control strategies to access ride comfort and road holding of the full-car suspension system are adopted as the passive, the sky-hook control and the quantitative feedback theory (QFT). Especially, the solid design of the QFT is undertaken in frequency domain. The suspension performance of the different controllers with two different MR dampers are evaluated and compared at random road excitation. It is shown that the peak value of the vertical acceleration of the suspension with the fast response MR damper is remarkably reduced compared with the slow response MR damper under the QFT control realization. It is also shown that between the skyhook and the QFT controller with the fast response MR damper, the acceleration power spectral density is reduced by 30% via the QFT controller.
Flexible ferroelectric capacitors based on Bi3.15Nd0.85Ti3O12/muscovite structureInorganic ferroelectrics which have low tensile strength and poor ductility are difficult to be bent. In this paper, in order to realize great toughness, the inorganic ferroelectric film was deposited on flexible muscovite (Mica) substrate. For efficiency and convenience, sol-gel method is adopted to fabricate the Bi3.15Nd0.85Ti3O12 (BNT) thin-film capacitor on flexible Mica substrate with SrRuO3 (SRO) electrode layer. The remnant polarization of the Pt/BNT/SRO/CFO/Mica capacitor achieves ~38 μC cm−2, which is larger than most BNT films prepared on hard substrates. No obvious fatigue phenomenon is observed for the BNT capacitor with 1010 switching cycles. The most important is that the Pt/BNT/SRO/CFO/Mica capacitor still owns relatively stable electrical properties when it is bent to 5 mm radius, showing an excellent bending performance for this structure. The flexible, anti-fatigue ferroelectric capacitor prepared in this paper is expected to get a wide range of application in flexible logic and elements for information storage, data processing and communication.
Ionic polymer metal composites for use as an organic electrolyte supercapacitorChoosing the right electrolyte for enhancement in energy storage and dissipation efficiencies of an electrochemical supercapacitor is a critical decision and a successful material choice could solve many issues faced by renewable energies such as wind and solar energy. Traditional aqueous electrolytes have been and continue to be used for their excellent electrolytic performance, but over past few decades, use of solid polymer electrolytes (SPEs) improved the performance of such devices by enhancing the power density and energy density. Platinum (Pt) incorporated ionic polymer metal composites (Pt-IPMCs) are being investigated for their applicability as solid polymer electrolyte (SPE) membrane for high-power supercapacitors as they have demonstrated improved performances in devices such as fuel cells, soft actuators etc. Pt nanoparticles were dispersed into a cubical Nafion membrane in a dense cluster (size distribution showing narrow). The Pt-IPMCs were tested using lithium hexafluorophosphate (LiPF6) in ethylene carbonate ((CH2O)2CO) and ethyl-methyl carbonate (C4H8O3) mixed in 2/1 volumetric ratio. Pt-IPMC resulted a lower internal voltage drop (0.15 V), higher ionic conductivity (0.46 mS cm−1), and higher specific capacitance (50.9 F g−1) compared with the commercial liquid electrolytes or Nafion 117. The average power density and energy density have improved by 19 and 17%, respectively by using Pt-IPMC electrolyte which could be ascribed to the decrease in the cell resistance or the increase of ionic conductivity. It should be noted that IPMC can be adopted as supercapacitor as well as soft actuator.
Structure and properties of novel antiferroelectric PbHfO3-Pb(Mg1/2W1/2)O3 single crystals grown from high-temperature solutionAntiferroelectric (AFE) materials with perovskite structure have attracted great interest due to their distinctive structural complexity and useful physical properties. So far, most studies have focused on polycrystalline materials. Compared with the preparation of ceramics and films, the growth of Pb-based AFE single crystals with high quality is a more challenging task because of the high melting point, incongruently melting and the volatilization of Pb-containing components at high temperatures. In order to develop new antiferroelectric materials for energy storage applications and understanding the mechanisms of phase transitions and domain structure, single crystals of a new AFE-AFE solid solution of PbHfO3-Pb(Mg1/2W1/2)O3 (PHf-PMW) were successfully grown for the first time by the high-temperature solution growth method using the mixtures of PbO-B2O3 and Pb3O4-B2O3 as complex flux, respectively, and the grown crystals were characterized in terms of their crystal structure, dielectric properties and domain structure. It was found that Pb3O4 as the main flux component is more favorable than PbO as it lowers the melting point of the system and provides a more stable growth, leading to PHf-PMW crystals of larger size, better quality, higher optical transparency and less defects or inclusions. The structural analysis by XRD shows an orthorhombic Pbam symmetry at room temperature for the grown crystals, which is of antiferroelectric nature. By comparing the sequence and temperature of the phase transitions to the PHf-PMW ceramics, the compositions of the grown crystals are estimated to be 0.99PHf-0.01PMW and 0.985PHf-0.015PMW, respectively. Compositional segregation is observed in the grown crystals, which can be attributed to the incongruently melting character on the one hand, and the differences in the ionic radius and electronegativity of the oxygen anion and various B-site cations in the crystal lattice on the other hand. The observation and analysis of the ferroic domains by polarized light microscopy based on optical crystallography reveal domain structures consisting of two sets of domains with extinction directions parallel to the 〈110〉cub direction, confirming the orthorhombic symmetry. This work provides new experimental strategies in growing the high-quality antiferroelectric crystals of complex perovskite structure and a better understanding of their structure and properties for both fundamental studies and potential applications in optoelectronics and energy storage.
Papers
Corrosion monitoring of prestressed concrete structures by using topological analysis of acoustic emission dataThe potential of topological data analysis (TDA) to aid acoustic emission (AE) in revealing early signs of corrosion in prestressed concrete is investigated. The AE generated by corrosion is quantified in terms of features, including cumulative energy, cumulative number of hits, and peak frequency. Shape (i.e. topological) characteristics of the AE datacloud, which may embed corrosion-related information, are then studied quantitatively using TDA. The proposed method was evaluated in accelerated corrosion testing of a prestressed concrete specimen. AE was recorded non-invasively on the concrete surface, with more than 600 000 hits observed over 118 cycles of accelerated corrosion (spanning 206 d). The large AE datacloud contained holes, which opened and closed near distinct points in the corrosion process. These holes were quantified using TDA, and shown to correlate with and provide early indications of certain corrosion mechanisms. The results highlight the potential of TDA to aid in extracting corrosion information from AE data. Further, with TDA aiding traditional AE monitoring, there is potential for early and reliable indication of concrete cracking, prior to the appearance of external visual signs.
Coupling of nonlinear shape memory polymer cantilever dynamics with focused ultrasound fieldResearch has found significant potential for ultrasound actuation of shape memory polymers (SMPs) in several fields such as biomedical and electronic devices among others. Example applications range from controlled drug delivery containers to soft robotics and flexible electronics located in otherwise inaccessible places or hazardous environments, where direct external heating is not possible. SMPs can be manipulated into any temporary shape and later recover to their stress-free permanent shape when triggered with external stimuli such as heat. Focused ultrasound (FU) has the ability to induce localized heating and activate multiple intermediate shapes and achieve complete shape recovery in the polymer, non-invasively and remotely. In addition, FU has a superior capability for temporal and spatial control of shape recovery by adjusting sample size, ultrasound frequency, exposure time and intensity as well as the position of ultrasound focusing. In this paper, indirect actuation of the thermally-induced shape-memory effect of SMPs by FU is studied theoretically and experimentally with a focus on the acoustic field, medium, geometric and material properties. The changes in thermomechanical properties, during FU actuation, are studied through dynamic mechanical analyzer tests. Using these properties, an analytical acoustic-thermo-elastic dynamic model is developed to predict the shape memory response of a SMP cantilever beam, considering acoustic and geometric nonlinearities. The governing equations of motion are derived using reduced order modeling and solved by perturbation techniques. Having obtained an analytical expression for the shape recovery of the beam as a function of acoustic parameters, experimental validations for a cantilever SMP beam exposed to FU are performed. The model has the ability to successfully estimate the variation in the amount of shape recovery due to the change in source frequency of the transducer and peak acoustic pressure field inside SMP domain without the need of analyzing any intermediary acoustic/thermal/elastic behavior.
Droplet formation study of a liquid micro-dispenser driven by a piezoelectric actuatorThe piezoelectric-driven noncontact jetting dispenser with the characteristics of high accuracy, efficiency and applicability has been widely applied in the microelectronics packaging field to produce small droplets. The process of droplet formation and separation is the key to successful jetting. In order to study the process and show the roles of system parameters in droplet formation, the paper runs some numerical simulations and analyzes the comprehensive effects of the system parameters on the morphological change of droplets by using two dimensionless parameters Weber and Reynolds. The simulation and experiment results show that the scale of system parameters is confirmed by the lower and upper limits of Weber according to different Reynolds. If Weber is bigger than the upper limit value or smaller than the lower limit value, the jetting failure like sputtering, satellite dots jetting or adhesion will occur. During the experiments, the system parameters should be adjusted to keep the values of Weber and Reynolds in the proposed scale. The findings in this paper can be used to guide the design and control of these piezoelectric driven dispensers.
The generalized self-consistent micromechanics prediction of the magnetoelectroelastic properties of multi-coated nanocomposites with surface effectA theoretical study on the effective magnetoelectroelastic (MEE) properties of the multi-coated nanocomposites is reported based on a generalized self-consistent model with surface MEE effect under far-field antiplane shear load, inplane electric load and inplane magnetic load. A rigorous analytical solution of overall generalized MEE stress and strain fields in each component is presented via the complex potential function theory. The closed-form solution of the effective MEE coefficients is obtained by using the average-field theory. Several existing and new results can be regarded as the special cases of the present solution. A comparison with other theoretical results shows good agreement, which illustrates the accuracy of the proposed method. Numerical examples reveal the size dependence of the effective MEE coefficients when the size of the coated fiber is at nanoscale. Several typical MEE composites with the epoxy matrix are investigated, and the influences of the microstructure parameters on the magnetoelectric coupling effect are discussed.
Bolt preload measurement based on the acoustoelastic effect using smart piezoelectric boltPrecise measurement of bolt preload force is particularly important in the assembly process of aviation equipment, which is directly related to the normal working performance and indicators of the equipment. According to the acoustoelastic effect, a model considering theoretical error and measurement error is proposed. The relationship between the change of time-of-flight (CTOF) and the bolt preload is established by the model. With the increase of the preload, the CTOF approximately increases linearly. Therefore, a smart piezoelectric bolt was developed. Piezoceramic transducer is embedded in the bolt head at pre-determined spatial locations. Experimental results show that the relative error of the smart bolt is about 1%. In addition, the influence of contact pressure and contact phase is discussed. The results show that the characteristic of smart piezoelectric bolt eliminates the effect of the couplant and makes the measurement more precise than the measurement performed using the ultrasonic probe. This method provides a promising way to measure the bolt preload.
Elastic shape morphing of ultralight structures by programmable assemblyUltralight materials present an opportunity to dramatically increase the efficiency of load-bearing aerostructures. To date, however, these ultralight materials have generally been confined to the laboratory bench-top, due to dimensional constraints of the manufacturing processes. We show a programmable material system applied as a large-scale, ultralight, and conformable aeroelastic structure. The use of a modular, lattice-based, ultralight material results in stiffness typical of an elastomer (2.6 MPa) at a mass density typical of an aerogel . This, combined with a building block based manufacturing and configuration strategy, enables the rapid realization of new adaptive structures and mechanisms. The heterogeneous design with programmable anisotropy allows for enhanced elastic and global shape deformation in response to external loading, making it useful for tuned fluid-structure interaction. We demonstrate an example application experiment using two building block types for the primary structure of a 4.27 m wingspan aircraft, where we spatially program elastic shape morphing to increase aerodynamic efficiency and improve roll control authority, demonstrated with full-scale wind tunnel testing.
Flight demonstration of aircraft wing monitoring using optical fiber distributed sensing system
We conduct flight demonstrations of aircraft monitoring by using optical fiber distributed sensing technique. We monitor a main wing of a flying test bed that is a middle-sized passenger jet. We use optical frequency domain reflectometry and long-length fiber Bragg gratings (FBGs). The sensing system measures the strain distribution profile within the FBGs with a mm order spatial resolution in real-time. Thanks to the high spatial resolution, we could observe local strain distributions due to the ribs of the wing. We also monitored strain distribution variations corresponding to various maneuvers during flight. We discussed the correlation with flight maneuvers and the interpretation of the monitoring data.
Machinability of Ni-rich NiTiHf high temperature shape memory alloyMachining of Ni-rich Ni50.3Ti29.7Hf20 (at%) high temperature shape memory alloys was evaluated under flood cooling conditions. Effects of various cutting speeds (between 20 and 120 m min−1), depth of cuts (between 0.4 and 1 mm), and the associated cutting forces on the work-piece surface quality and tool wear of this alloy are presented. Experimental data demonstrates that abrasion and adhesion were the predominant wear mechanisms leading to extreme wear in a short machining time. Thermal softening mechanism dominated the trend of cutting forces until 95 m min−1 cutting speed. Beyond this speed, force components sharply increased resulting from extreme tool wear. Chip breakability of this alloy is much better when compared to NiTi shape memory alloy.
Nonlinear dynamics of shape memory alloys actuated bistable beamsThe phenomenon of bi-stable behaviour has been widely used in the structural design, as it can provide large deformation by switching between two stable equilibrium positions. This paper aims to investigate the intrinsic nonlinear dynamic characteristics of an actively controlled bistable beam using a simplified spring-mass model. The dynamic model for an active (heated) SMA wire driven bistable beam is established based on a polynomial constitutive equation to describe the thermomechanical behaviour of the shape memory alloy. The actively controlled bistable beams are designed, fabricated and experimentally tested to achieve the morphing behaviour snapping-through form one position to another. The results obtained from the experimental testing and the theoretical simulation are compared to validate the proposed model. Dynamic behaviour of the proposed SMA wires actuated bistable beam under varying external excitation is investigated to show the influence of the thermomechanical loadings. Analysis of the experimental data and simulation results shows that the SMA wires actuated bistable structure can be well-performed for the bistable switching. It also approved that the different behaviours of the system, including periodic responses, complex responses and chaos can be accurately predicted using the proposed simplified model.
Experimental and Monte Carlo simulation studies on percolation behaviour of a shape memory polyurethane carbon black nanocompositeElectro-active shape memory polymer nanocomposite from polyurethane matrix with carbon black fillers was synthesized and characterised for its electrical properties. The polyurethane matrix possesses high transition temperature, which enables it to be a candidate for high temperature applications. The carbon nanoparticle content was varied with conductivity measured at each instance, and a percolation threshold value of 6% was observed experimentally. The conductivity phenomenon was studied using Monte Carlo simulation approach on a pseudo random model of the system, developed using constrained optimization by linear approximations algorithm in visual C language platform. The probability of three dimensional network formations of carbon particles was evaluated for varying filler loading and percolation threshold of 6.2% was obtained from the model. The conductive networks formed have resulted in multiple electron paths, generating volumetric heating of the system while connected with a known power supply. This joule heating was used as stimuli for activating the shape memory behaviour by passage of electric current. High shape recovery efficiency (>95%) observed with faster recovery time (25 s), along with high transition temperature (85°) can help to qualify the system for space applications.
A high-performance soft actuator based on a poly(vinylidene fluoride) piezoelectric bimorphCompared with a single piezoelectric poly(vinylidene fluoride) (PVDF) sheet, a bimorph can enhance driving performance. The main aim of this work is to study a soft piezoelectric bimorph as an actuator used in a soft sail. PVDF samples were prepared using a high-temperature solvent evaporation method and were then drawn and poled. The crystalline phase, mechanical properties, piezoelectric property and energy-harvesting performance were analyzed. A PVDF piezoelectric bimorph was designed. The capacity of deformation of the parallel bimorph with a pulsed electric field was studied. The deformation of the sample increased almost linearly, and the deformation performance was obvious with the increase in voltage. To evaluate its driving performance in the engineering model, a sail made of Kapton was produced, and the PVDF bimorph was used as an actuator to drive the sail. The deformation was observed by a Video-Simultaneous Triangulation and Resection System. Furthermore, the finite element method was used to further understand the actuation effect of the Kapton sail matrix and PVDF bimorph actuator according to three different laying methods.
Embedded metallized optical fibers for high temperature applications*Embedding fiber optics in metal components could enable new capabilities such as active monitoring of spatially distributed strain. Ultrasonic additive manufacturing is a suitable technique for embedding fiber optics because it allows fibers to be embedded in metals without melting and without the use of epoxy. However, for harsh environments that could have high temperatures or high radiation doses, traditional polymer-coated fibers cannot survive for extended periods of time. This work demonstrates successful embedding of commercially available copper-, nickel-, and aluminum-coated fibers into aluminum without any observable damage to the fiber. Copper-coated fibers embedded in copper show adequate light transmission, although residual strain could not be resolved. With further processing improvements, fibers embedded in copper or other high-temperature materials could enable even higher temperature operation. Optical transmission and spatially distributed strain were measured in the fibers embedded in aluminum. Measurements were taken after embedding and during heating to temperatures greater than 500 °C. Within the embedded region, both the copper- and aluminum-coated fibers showed strain that matched the expected strain in the surrounding aluminum matrix during heating. This suggests a strong interfacial bond strength that exceeds the maximum estimated fiber strain of 1.2% (871 MPa tensile stress). This demonstration of embedded fibers that can survive high temperatures and remain bonded to the metal matrix is the first step toward embedded fiber optic sensors for harsh environment applications.
Nonlinear free vibration of graphene platelets (GPLs)/polymer dielectric beamNonlinear free vibration of graphene platelets (GPLs) reinforced dielectric composite beam subjected to electrical field is analysed. Effective medium theory is adopted to approximate the overall Young's modulus and dielectric permittivity of the GPLs reinforced composite. The Poisson's ratio and mass density of the composites are estimated by rule of mixture. Based on Timoshenko beam theory, governing equations for beam vibration are established by using Hamilton's principle and nonlinear von Kármán strain–displacement relationship. Numerical solution to the governing equations is obtained through differential quadrature method. The effects of GPL concentration and size, and the electrical voltage and AC (alternating current) frequency upon the nonlinear vibration of the GPL reinforced composite beam are investigated. The results demonstrate that there exists a threshold for GPL weight fraction in the polymer matrix, above which the electrical field plays a dominant role on the vibration behaviours. Increasing the voltage of the electrical field will enhance the ratio of nonlinear frequency to linear frequency. A transition region for the AC frequency is observed, within which the vibration characteristics varies dramatically. The analysis conducted in present work is envisaged to provide guidelines for designing GPL reinforced smart composites and structures.
2D–3D interface coupling in the time domain spectral element method for the adhesive layer effects on guided wave propagation in composite platesA new approach for numerical simulation of the wave propagation in a composite plate is presented in this paper. Problem is realized by the 2D–3D coupled time domain spectral element method. All components used in the simulation are decomposed from each other. A connection between them is guaranteed by the interface elements realized by Lagrange multipliers. With this type of scheme, one can avoid a modelling of all the components by the three-dimensional (3D) spectral elements. In particular, the computation time can be reduced by using two-dimensional (2D) elements for adhesive layer modelling. Otherwise, 3D elements are very inefficient because a convergence of Central Difference Time Integration Method applied for solving an equation of motion is strongly correlated with the size of the smallest element. Numerical calculations were performed for the composite plate modelled by the 3D solid elements with a piezoelectric transducer bonded to the plate by the adhesive layer modelled by 2D shell elements. The simulations were carried out for an adhesive layer of various thickness for the excitation frequency in the range of 50–200 kHz. The presented model was verified by experimental data obtained by the laser vibrometer.
Abnormal grain growth in annealing cast Cu–Al–Mn–V alloys and their superelasticityMetals are usually difficult to fabricate bulk materials with a large grain size over cm-scale only through heat treatment with neither directional solidification nor macroscopic deformation. This paper reports a novel method to obtain large grains and single crystals over cm-scale only through simply annealing polycrystalline cast Cu–Al–Mn–V shape memory alloys. The results show that the abnormal grain growth (AGG) directly occurs when cast alloys are annealed at 1173 K, and ultra-large grains and single crystals are obtained after quenching. The AGG results from unique microstructure of cast Cu–Al–Mn–V alloys. All cast alloys consist of L21-Cu2AlMn parent and completely coherent bcc A2(V) nanoparticles due to bcc phase separation. The results further show that the dissolution of A2(V) nanoparticles into the matrix during annealing results in a continuous misorientation gradient within the matrix grains. It may provide the driving force for the rapid migration of grain boundaries, leading to the AGG. Furthermore, the single crystals close to exhibit good superelasticity. Cu-13.7Al-8.6Mn-1.4 V single crystal shows the largest full superelasticity of 7.0%, and Cu-13.2Al-9.8Mn-0.7 V single crystal exhibits the largest superelastic strain of 5.4%.
Structured magnetic circuit for magnetorheological damper made by selective laser melting technologyEddy currents are the main reason causing for the long response time of a magnetorheological (MR) damper. Eddy currents are often unwanted parasitic phenomenon for many electromagnetic machines working with an alternating magnetic field. Their reduction can be secured by the use of material with high electrical resistivity such as ferrites or soft magnetic composites. These materials, however, exhibit bad mechanical properties and cannot be used in mechanically loaded parts. Eddy currents can also be reduced by the appropriate structure which must secure high conductivity for the magnetic flux but low electrical conductivity for the electric current flowing perpendicularly to the magnetic flux. This leads to complex structures which, in most cases, cannot be manufactured by conventional methods. This paper describes the design, manufacturing and verification of simulations of the magnetic circuit for a MR damper. Structured magnetic cores printed by selective laser melting technology connects the benefits of low-carbon steel (good mechanical properties, high magnetic saturation and high relative permeability) with benefits of sintered materials (high electric resistivity). The results proved that using the potential of additive manufacturing can not only reduce the eddy currents (and thus shorten the response time and reduce losses), but significantly reduce the weight as well. This technology enables the combination of performance parameters of electromagnetic machines, which cannot be reached by any other existing method.
Shear thickening gel reinforced flexible polyurethane foam and its enhanced propertiesCushioning energy absorbing materials are developing towards lightweight and high specific strength. Therefore, how to ensure the lightweight and high strength of materials is an important issue of common concern to researchers. In this paper, a stretchable shear thickening gel/polyurethane foam composite material, with excellent shear hardening and energy absorption characteristics, was prepared by one-step foaming method. The strain rate sensitivity of the composite was 1.5–1.9 times than that of the pure polyurethane foam. Importantly, the addition of shear thickening gel increased the specific strength and specific energy absorption of the composite material by 82% and 96% respectively compared with pure polyurethane foam.
Solvent-assisted electrospun fibers with ultrahigh stretchability and strain sensing capabilitiesLarge strain flexible strain sensors have recently been the focus of many studies due to their wide range of applications in wearable technologies. However, development of a thin, conformable, and flexible strain sensor with a high maximum stretchability and a high gauge factor has still remained a challenge. In resistive-type sensors specifically, there is a trade-off between these two competing factors which has left a gap in development of large strain flexible strain sensors. To increase the sensitivity of the sensor, tuning the microstructure of the sensor through introducing a larger surface area is suggested. Using a solvent-assisted electrospinning technique and a highly stretchable copolymer of styrenebutadiene-styrene, super elastic mats composed of microfibers with a large surface area are obtained. Coating the fibers with different conductive materials and coating methods, a flexible strain sensor able to detect up to 1000% strain is fabricated. The sensors also show low hysteresis under cyclic-induced applied loadings.
Autonomous origami: pre-programmed folding of inkjet printed structuresSelf-folding, whereby a 2D net autonomously folds into a pre-ordained 3D shape when exposed to a stimulus, shows potential, in a manner similar to 3D printing, as a means of easily customisable digital manufacture. It also presents some inherent advantages over conventional additive manufacturing techniques, such as the low cost associated with mass-production of polymer sheets and coatings, the compatibility with most planar manufacturing techniques, and the ease of storage and transportation. A self-folding mechanism was developed by inkjet printing silver nanoparticle suspensions onto polyethylene terephthalate (PET) sheets. By providing sufficient electrical power to the printed tracks, resistive heating causes folding to occur along the printed silver lines. A bilayer strip model was adapted to analyse the steady-state fold angle of the PET substrate, which shows good qualitative agreement, and reasonable quantitative agreement, with the experimental data. Furthermore, inkjet-printed silver tracks are known for a significant reduction in resistivity as the sintering temperature increases. Therefore, a power control system that utilises a real-time resistance sensor was developed to enable power reference tracking. The developed mechanism was able to achieve folds up to 90° and a fast actuation time of 35 s when 2.25 W was provided to a 3 mm by 40 mm silver track.
Fabrication of bagel-like graphene aerogels and its application in pressure sensorsIn this study, a new bagel-like graphene aerogel composed of graphene sheets is reported. This bagel-like graphene aerogel was fabricated by a droplet containing graphene oxide sheets, which had an impact on the coagulation bath of the mixed ethanol and hydrochloric acid. During the impact process, the graphene oxide droplet locked the ripple of the coagulation bath while forming a special structure with the stagnating ripple, which was gradually transformed into a bagel-like graphene oxide hydrogel. Then, this graphene oxide hydrogel was processed by reduction and freeze drying to obtain a small and light-weight bagel-like graphene aerogel. As characterized by Raman spectrum, XRD and XPS, we confirmed that graphene oxide sheets were effectively reduced. The excellent electrical conductivity and stable mechanical properties of this bagel-like graphene aerogel were experimentally measured. We found that it could be applied as piezoresistive pressure sensors with high sensitivity at low pressure, wide measurement range and good stability. As confirmed by SEM, this outstanding sensing property was attributed to the aerogel's special lamellar multi-layered microstructure, which played a key role in the piezoresistive working mechanism.
Development of a novel magnetorheological fluids transmission device for high-power applicationsA novel magnetorheological (MR) fluids transmission device for high-power applications is designed, simulated and experimented. The transmission device is implemented of multi-hollow drive disc with magnetic conductive columns and adopts water cooling method to heat dissipation. In this paper, firstly, a novel hollow transmission disc with magnetic conductive columns is proposed, and the structure of the high-power MR fluid transmission device is determined. And then, the magnetic circuit is designed in detail, and the magnetic field distribution of the transmission device is analyzed by the method of finite element. Finally, a prototype of the transmission device is fabricated and several tests are carried out to evaluate the torque transmission, time response and temperature rise of the prototype. The results show that the proposed MR transmission device can produce a maximum output torque of 1880 N m and possesses a high slip power of up to 70 kW.
The following article is OPEN ACCESS
Thermomechanical behavior of shape memory alloy metal matrix composite actuator manufactured by composite extrusionContinuous composite extrusion represents a new possibility for the manufacturing of shape memory alloy metal matrix composites (SMA-MMC). During the process SMA wires are embedded into aluminum or magnesium profiles by means of modified porthole dies. Due to the high flexibility regarding the profile geometry, the materials as well as number, thickness and position of the SMA elements, the process can be used for the generation of a profile integrated bending function. The bending function of the actuator profile depends on the temperature and is thermally activated. The parameters influencing the behavior of the manufactured composited actuators are experimentally investigated. It is found that the radius of curvature mainly depends on the recovery stress and the eccentric position of the SMA wire as well as on the bending stiffness of the actuator profile. The bending mechanism and the experimental results are described by the use of an analytical model as well as a finite element analysis. Based on the results the analytical model is used for the targeted design of a profile with multiple embedded NiTi wires, which is able to perform a repeatable, pure elastic deflection within a defined temperature range between room temperature and 75 °C.
An inertial piezoelectric actuator with miniaturized structure and improved load capacityAn inertial actuator that improves load capacity within a miniaturized structure has drawn wide attention. This work proposes an inertial piezoelectric linear actuator and investigates a method that improves its load capacity. The structure and operational principle of the actuator are introduced. A dynamic model of the system is established that simulates the stepping characteristics. The dominant parameters affecting load capacity are discussed in detail. A prototype was manufactured and its main performance features tested. The experimental results confirm that the proposed actuator achieves a load capacity of 3.65 N, a resolution of 0.47 μm, and a speed of 6.15 mm s−1, despite its compact size of Φ 9 mm × 27 mm. The actuator has an improved load capacity given its smaller configuration than those reported in the literature. The model established provides a theoretical guide to the design of similar inertial actuators and may be used to predict and evaluate their load capacity.
Multiphysics simulation of the aspherical deformation of piezo-glass membrane lenses including hysteresis, fabrication and nonlinear effectsIn this paper we present and verify the nonlinear simulation of an aspherical adaptive lens based on a piezo-glass sandwich membrane with combined bending and buckling actuation. To predict the full nonlinear piezoelectric behavior, we measured the nonlinear charge coefficient, hysteresis and creep effects of the piezo material and inserted them into the FEM model using a virtual electric field. We further included and discussed the fabrication parameters—glue layers and thermal stress—and their variations. To verify our simulations, we fabricated and measured a set of lenses with different geometries, where we found good agreement and show that their qualitative behavior is also well described by a simple analytical model. We finally discuss the effects of the geometry on the electric response and find, e.g. an increased focal power range from ±4.5 to when changing the aperture from 14 to .
An iterative approach for analysis of cracks with exact boundary conditions in finite magnetoelectroelastic solidsAn iteration approach in combination with the boundary element method is proposed to analyze a crack with exact crack face boundary conditions (BCs) in a finite magnetoelectroelastic solid. The crack opens under an applied load and the opened cavity is considered as a single domain filled with air or vacuum. The electric and magnetic fields inside a crack cavity affect the crack opening displacement (COD), which is a geometrically nonlinear problem. When establishing a boundary integral equation for inner and outer domains bounded by opening crack faces, nearly singular integrals occur due to the very thin domain of a crack cavity. However, the nearly singular integrals require no special treatment by employing intelligent adaptive algorithms in software Mathematica. The proposed approach is based on iteration of boundary elements for a crack-cavity domain and sub-region boundary elements for an outer magnetoelectroelastic solid with the crack faces changing during the iterative process. In this approach, exact crack face BCs are used in iteration, and the exact electric displacement and magnetic induction across the crack face as well as the COD can be determined. Furthermore, extended stress intensity factors are calculated and finally, the effects of BCs and the crack size are discussed.
The following article is OPEN ACCESS
Quadruple-shape hydrogelsThe capability of directed movements by two subsequent shape changes could be implemented in shape-memory hydrogels by incorporation of two types of crystallizable side chains. While in non-swollen polymer networks even more directed movements could be realized, the creation of multi-shape hydrogels is still a challenge. We hypothesize that a quadruple-shape effect in hydrogels can be realized, when a swelling capacity almost independent of temperature is generated, whereby directed movements could be enabled, which are not related to swelling. In this case, entropy elastic recovery could be realized by hydrophilic segments and the fixation of different macroscopic shapes by means of three semi-crystalline side chains generating temporary crosslinks. Monomethacrylated semi-crystalline oligomers were connected as side chains in a hydrophilic polymer network via radical copolymerization. Computer assisted modelling was utilized to design a demonstrator capable of complex shape shifts by creating a casting mold via 3D printing from polyvinyl alcohol. The demonstrator was obtained after copolymerization of polymer network forming components within the mold, which was subsequently dissolved in water. A thermally-induced quadruple-shape effect was realized after equilibrium swelling of the polymer network in water. Three directed movements were successfully obtained when the temperature was continuously increased from 5 °C to 90 °C with a recovery ratio of the original shape above 90%. Hence, a thermally-induced quadruple-shape effect as new record for hydrogels was realized. Here, the temperature range for the multi-shape effect was limited by water as swelling media (0 °C–100 °C), simultaneously distinctly separated thermal transitions were required, and the overall elasticity indispensable for successive deformations was reduced as result of partially chain segment orientation induced by swelling in water. Conclusively the challenges for penta- or hexa-shape gels are the design of systems enabling higher elastic deformability and covering a larger temperature range by switching to a different solvent.
Uncertainty analysis of dielectric elastomer membranes under electromechanical loadingThe uncertainty in modeling finite deformation membrane electromechanics is analyzed by comparing low and high fidelity models against data on the dielectric elastomer VHB 4910. Both models include electrically and mechanically induced stress during transverse deformation of the membranes. The low fidelity model approximates deformation to be homogeneous while the high fidelity model includes a more accurate kinematic assumption of inhomogeneous deformation. We illustrate the importance of model fidelity with regards to parameter uncertainty and the associated propagation of errors in predicting membrane forces and charges in realistic actuator configurations. Both the low and high fidelity models are shown to accurately predict membrane forces and charges under different applied displacements and voltages. However, there are significant differences in the estimation of the dielectric constant used to model the membrane electromechanics. Bayesian statistics are used to quantify the uncertainty of the modeling approaches in light of both force–displacement and charge–voltage measurements. We quantify the hyperelastic, electromechanical coupling, and dielectric model uncertainties self-consistently using all mechanical and electrical experiments conducted on the 3M elastomer VHB 4910. We conclude that the low fidelity model is useful for system dynamic and control applications yet is limited in self-consistent predictions of both forces and charges from applied displacements and voltages. In comparison, the high fidelity model provides a more accurate description of the electromechanical coupling and dielectric constitutive behavior, but requires more computational power due to finite element discretization. In addition, the high fidelity modeling illustrates that a deformation dependent dielectric constant is necessary to self-consistently simulate both force–displacement and charge–voltage data.
Clip-brazing for the design and fabrication of micronewton-resolution millimeter-scale force sensorsWe present clip-brazing as a new method to construct millimeter-to-centimeter-scale metal structures with micron-scale precision that is fast, scalable and extremely low-cost. Small structures with demanding requirements on both dimensional tolerances and dynamic force responses to time-varying loads are difficult to fabricate and expensive to iteratively prototype. The technique introduced here enables precise placement of strong metallic brazed bonds to create 3D structures with micrometric accuracy, which in this work is exemplified through the design and construction of a broadband micronewton-resolution force-sensing device. The fabrication method uses tensioned clips made from a silver brazing alloy wire to accurately place and control the volume of the metal that joins and supports the pieces that compose the micro-structures. The use of clips also allows the simultaneous fusion of all the connections in the structure during a single heating sequence, reducing tolerance stack-up. To analyze the quality and strength of the brazes, we employed scanning electron microscopy (SEM) on cross-sections and tensile testing on dogbone-shaped sample pieces, respectively. After proper calibration, the functionality of the constructed micro-force-sensing system was analyzed and demonstrated using constant a priori known weights and the vertical periodic forces produced by an 83 mg flapping-wing microrobot (including a 3 mg attachment truss). The static tests, in combination with solid-mechanics analyses and simulations based on finite-element analysis (FEA), provide compelling evidence of the high accuracy and precision of the force sensing system for frequencies below 167.5 Hz. Furthermore, the shape characteristics and average values of the measured periodic signals are compared to computational fluid dynamics (CFD) simulations and validated for two sets of flapping angles across the frequency range from 55 to 100 Hz. These results validate the proposed approach as a viable tool for microrobotic design and fabrication.
Development and validation of a fatigue testing setup for dielectric elastomer membrane actuatorsDielectric elastomers (DEs) represent a transduction technology with high potential in many application areas, including industry, due to their low weight, flexibility, and low energy consumption. For industrial applications, it is of fundamental importance to quantify the lifetime of DE technology, in terms of both electrical and mechanical fatigue, when operating in realistic environmental conditions. This work contributes toward this direction, by presenting the development of an experimental setup which allows systematic fatigue testing of DE membranes. The setup permits to apply both mechanical and electrical stimuli to several membranes simultaneously, while measuring at the same time their mechanical (force, displacement) and electrical response (capacitance, resistance). The setup allows to test up to 15 DE membranes at the same time. The setup can be placed in a climate chamber, in order to investigate the fatigue mechanisms at different environmental conditions, i.e. in terms of temperature and humidity. After describing the setup, first fatigue results are shown for several DE membranes loaded at different constant voltage values, and mechanically cycled for several hundred thousands of cycles.
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Bi-stable hybrid composite laminates containing metallic strips: an experimental and numerical investigationThis study scrutinizes the static characteristics of a new category of bi-stable hybrid composite laminates (BHCLs) that contain multiple metallic strips (aluminum) distributed along the middle layer of a carbon fiber reinforced epoxy laminate. With this new class of BHCLs, the direction of curvature of the laminates does not change during the snap-through between the two stable states, unlike the conventional bi-stable cross-ply laminates. The laminates were modeled using finite element analysis and were experimentally validated. BHCLs with two to five metallic strips were fabricated for this purpose. The effect of the number, width, and thickness of the metallic strips on the static characteristics of the laminate were numerically investigated using ABAQUS. Further, the curvatures, out-of-plane displacement, and static snap-through load of the laminates were determined experimentally. The results showed a strong relationship between the residual curvature and the load-carrying capability of the laminate and the number, width, and thickness of the metallic strips, as well as the laminate geometry. Knowledge of this characteristic will allow designers to tune the parameters for a given application and to achieve the desired performance. Good qualitative and quantitative agreement was observed between the numerical and the experimental results.
Flexible and colorless shape memory polyimide films with high visible light transmittance and high transition temperatureColorless shape memory polyimide (CSMPI) has potential applications in broad fields, especially in advanced optoelectronics due to the excellent optical transparency, shape memory effect and high temperature resistance. In this work, high flexible dianhydrides and fluorine-containing diamines were used to synthesize CSMPI, which simultaneously combined great shape memory performance with high optical transparency. The effects of monomer ratios and imidization temperatures on the molecular structure and properties were investigated. Moreover, the CSMPI film possesses a higher glass transition temperature (Tg) of 234 °C, compared with the reported transparent shape memory polymers. Most importantly, the transmittance of CSMPI film is 87%–90% at 450–800 nm, meeting the requirements of heat resistance and transmittance of the substrate. Both shape recovery and shape fixity are over 97%. Flexible and colorless CSMPI films severed as substrates provide more potential in optoelectronic devices such as OLED and OPV, etc.
Broadband, large scale acoustic energy harvesting via synthesized electrical load: I. Harvester design and modelWith the rise of Internet-of-Things and connected devices, the need for self-powered wireless sensor nodes is ever increasing. One promising technology for self-powered sensor nodes in noisy environments is acoustic energy harvesting: deriving energy from ambient sound. Existing acoustic energy harvesters are typically based on resonant structures, yielding narrowband, and therefore low-energy, collection from broadband noise sources. In addition, existing acoustic energy harvesters tend to exhibit MEMS-scale sizes, with consequently low power outputs. This two-part work addresses the size and bandwidth of such harvesters. A large-scale acoustic energy harvester is developed, based on piezoelectric PVDF (polyvinylidene fluoride) film 100 cm2 in size. The harvester is designed to minimize reactive impedance, allowing for circuit loading for broadband energy harvesting in Part II of this paper. An energy-based dynamic analysis of the harvester driven by an acoustic source yields an equivalent circuit model and subsequently a Thévenin equivalent model of the harvester. The model is validated by experiments including acoustic and electric measurements, laser Doppler vibrometry, and finite element analysis. It is used to develop loadings in Part II.
Broadband, large scale acoustic energy harvesting via synthesized electrical load: II. Electrical loadExisting acoustic energy harvesters are typically resonant structures operated with matched loads, yielding narrowband, and hence low, energy collection from broadband noise sources. Additionally, existing acoustic energy harvesters tend to exhibit MEMS-scale sizes, with correspondingly low power collection and outputs. In contrast, this paper presents the combined real and reactive electrical loading of a wide-area harvester which yields efficient broadband harvesting at higher power. Building on the harvester designed and modeled in Part I, this paper develops the reactive loading and its operational amplifier implementation, illuminating along the way several design issues critical to optimal performance and stability. The loading enables an experimental harvester capable of harvesting acoustic energy with an efficiency of 0.3%–3% over the frequency range of 50–500 Hz. The harvester is demonstrated in a real-world scenario, collecting approximately 2.3 μJ per aircraft takeoff event in an airport environment. This demonstrates the efficacy of acoustic energy harvesting energy and its potential for powering wireless sensor nodes in real-world noisy environments. While the loading is implemented here with lossy operational amplifier circuits, it is amenable to implementation with efficient power electronics.
Soft-smart robotic end effectors with sensing, actuation, and gripping capabilitiesSoft and smart robotic end effectors with integrated sensing, actuation, and gripping capabilities are important for autonomous and intelligent grasping and manipulation of difficult-to-handle and delicate materials. Grasping and actuation are challenging to achieve if using only one opto-mechanical tactile sensor. It is highly desirable to equip these useful sensors with multimodal actuation and gripping functionalities. Current electroadhesive (EA) grippers, however, cannot differentiate object size and shape, nor can they grasp concave or convex objects. In this paper, we present TacEA, an integration of a pneumatically actuated visio-tactile (TacTip) sensor and a stretchable EA pad, resulting in a monolithic soft-smart robotic end effector with concomitant sensing, actuation, and gripping capabilities. This soft composite-materials device delivers the first soft tactile sensor with actuation and gripping capability and the first EA end effector that can sort different 2D object sizes and shapes with one touch, and which can actively grasp flat, concave and convex objects. The soft-smart TacEA is expected to widen the capabilities of current tactile sensors and increase EA end effector use in material handling and in processing and assembly lines.
Design and fabrication of a high-speed linear piezoelectric actuator with nanometer resolution using a cantilever transducerA high-speed linear piezoelectric actuator with nanometer resolution using a cantilever transducer is designed, fabricated and tested. This actuator includes end cap, flange, fixed part, longitudinal and bending PZT ceramics. They are clamped to make up a cantilever transducer. The first longitudinal vibration and second bending vibration of the transducer are excited by two alternating current signals with a phase difference of 90°. Then, elliptical vibrations are formed on the driving foot and a high-speed linear motion of the slider is obtained under friction coupling effect. The actuator generates bending deformation when a direct current (DC) signal is applied to the bending PZT ceramics and a micro step with nanometer scale is achieved. The principles are illustrated in detail. Finite element method is used to confirm the desired vibration modes and analyze the motion characteristics of the actuator. A prototype is fabricated and it acquires the no-load speed of 593 mm s−1 under voltage of 300 Vp–p. The maximum output force of the actuator is tested as 30 N. The proposed actuator obtains a displacement resolution of 35 nm under DC voltage of 3 V. The tested results show that the proposed actuator has the abilities of fast and precise motions simultaneously.
An algebraic reconstruction imaging approach for corrosion damage monitoring of pipelinesIn this paper, an algebraic reconstruction technique is presented for corrosion damage monitoring in steel pipes by using helical guided ultrasonic waves. To validate the proposed approach, numerical simulations as well as experimental tests were carried out. For the numerical simulations, a finite element model was created using ABAQUS software to simulate wave propagation in a steel pipe. The model simulates corrosion damage by reducing the thickness of the pipe in a selected location. Experimental tests were conducted on a steel pipe instrumented with a network of six low-profile piezoelectric transducers. Reconstructed images from both the numerical simulations and experimental tests accurately localized the simulated damages. These results suggest that the proposed imaging algorithm has the potential to be effectively used for continuous monitoring of pipelines.
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Temperature-controlled reversible pore size change of electrospun fibrous shape-memory polymer actuator based meshesFibrous membranes capable of dynamically responding to external stimuli are highly desirable in textiles and biomedical materials, where adaptive behavior is required to accommodate complex environmental changes. For example, the creation of fabrics with temperature-dependent moisture permeability or self-regulating membranes for air filtration is dependent on the development of materials that exhibit a reversible stimuli-responsive pore size change. Here, by imbuing covalently crosslinked poly(ε-caprolactone) (cPCL) fibrous meshes with a reversible bidirectional shape-memory polymer actuation (rbSMPA) we create a material capable of temperature-controlled changes in porosity. Cyclic thermomechanical testing was used to characterize the mechanical properties of the meshes, which were composed of randomly arranged microfibers with diameters of 2.3 ± 0.6 μm giving an average pore size of approx. 10 μm. When subjected to programming strains of εm = 300% and 100% reversible strain changes of εʹrev = 22% ± 1% and 6% ± 1% were measured, with switching temperature ranges of 10 °C–30 °C and 45 °C–60 °C for heating and cooling, respectively. The rbSMPA of cPCL fibrous meshes generated a microscale reversible pore size change of 11% ± 3% (an average of 1.5 ± 0.6 μm), as measured by scanning electron microscopy. The incorporation of a two-way shape-memory actuation capability into fibrous meshes is anticipated to advance the development and application of smart membrane materials, creating commercially viable textiles and devices with enhanced performance and novel functionality.
Design and benchmarking of a low-cost shape sensing spar for in situ measurement of deflections in slender lifting surfaces in complex multiphase flowsShape sensing is a means by which to infer or reconstruct the deflections experienced by a flexible body. These deflections can be clear indicators of the operating conditions of the structure itself. The work presented in this paper proposes a robust, inexpensive, and accurate method for the shape sensing of a cantilevered body using a first-generation shape sensing spar. The shape sensing spar is benchmarked with static point loads and unsteady distributed loads in the context of a flexible hydrofoil. Results reveal maximum measurement error uncertainties of 0.2 cm in bending and 0.49° in twisting using a sampling rate of 500 Hz, making the proposed method competitive with optical methods for steady state measurements, and more suitable than optical methods for dynamic measurements because of the high sampling rate. Moreover, the shape sensing spar provides a method for deflection measurement in complex multiphase flows where optical methods do not perform well. Future improvements and applications for the shape sensing spar are outlined.
Study on the application of post-embedded piezoceramic transducers for crack detection on earthquake-damaged RC columnsIn this study, the post-embedded piezoceramic transducers are used to perform structural health monitoring (SHM) and detect crack damage on the reinforced concrete (RC) column. The piezoceramic transducers are utilized as actuators and sensors, respectively. To investigate the use of the piezoceramic transducer in detecting crack damage in RC columns, SHM tests are performed on three full-size RC column specimens with various failure modes under cyclic loading. The sensors are installed at two depth ranges (40–50 and 70–80 mm) beneath the surface of the column to investigate the effect of the sensor depth on the damage index. In this study, the energy and amplitude-based damage indexes are developed. Both approaches follow the same trend under various drift ratios of the specimen. However, the value of energy-based damage index is much higher than the amplitude index for all peak drift ratio of the specimen. From different depth range of piezoceramic transducers, this study recommends a depth of 80 mm as optimal for post-embedded piezoceramic transducers, since it receive more stable signals in various frequencies. In the proposed health monitoring approach using piezoceramic transducers, the equation to predict the maximum residual crack width and damage index smart aggregates are developed. The normalized damage index equation which in this study is referred as 'crack damage index' is introduced and used to calculate the limiting value for each damage level. The suggested value of the crack damage index for each damage level is also provided. The energy, strength and stiffness reduction factors for each damage level, which correlate with the crack damage index, are also presented. These results demonstrate that the proposed post-embedded piezoceramic transducers has the potential to be used as a tool for SHM on an RC column.
Experimental test on an RC beam equipped with embedded barometric pressure sensors for strains measurementThe current trend in structural health monitoring (SHM) is to install increasingly large numbers of distributed, heterogeneous types of sensors, for a timely and exhaustive detection of any possible damage scenario evolving in the system. These sensors should be low-cost, easy to install, robust and durable. Among others, strain remains one of the most straightforward measurands for monitoring the state of a structural element and for assessing its health condition. However, for application to reinforced concrete structures, currently available strain sensing devices, such as electric strain gauges or fibre optic sensors, do not fully satisfy the aforementioned requirements, generally proving difficult to install, fragile and expensive. In this paper, an innovative monitoring technology, called Smart Steel System (S3), is proposed that measures strains in reinforced concrete members, by incorporating commercial barometric pressure MEMS sensors in appropriate sealed cavities embedded in the reinforcing steel bars. The results of an experimental campaign are reported, in which a reinforced concrete beam, instrumented with both S3 devices and conventional electrical strain gauges, is subjected to increasing loading and unloading cycles until collapse. The tests show the superior robustness of the S3 system during construction and loading as well as its good sensing accuracy, demonstrating its potential for a massive use in SHM applications.
Crack width study for two-span RC Beams strengthened with Ni–Ti strands under cyclic loadingAlthough cracking is normal in reinforced concrete structures, caution should be exercised to prevent impairment of the proper function or durability of the structures or cause an unacceptable appearance in the structures. Consequently, crack width calculations have been especially observed in service limit states. Recently, smart materials such as shape memory alloys (SMAs) are considered in civil engineering. SMAs are a class of metallic alloys that have the unique property of being able to undergo large amounts of plastic strain while remaining elastic. The main objective of this paper is to investigate the crack pattern of continuous reinforced concrete (RC) beams strengthened by Ni–Ti strands. Experimental service crack widths were compared with theoretical values obtained from building codes provisions and formula proposed by previous literature. It was shown that superelastic strands had a significant effect on the occurrence of cracks and so the cracking moment of SMA RC beams increased. Verification of theoretical equations virtually resulted in overestimated crack widths for strengthened beams. Besides, the high recovery capacity of crack widths is the most important superiority of SMA RC beams.
Technical Notes
Modelling of love-type wave propagation in piezomagnetic layer over a lossy viscoelastic substrate: Sturm–Liouville problemWe propose an analytical solution for the propagation of Love-type surface seismic waves in a piezo-composite smart structure. A model describing the Love-type wave propagation in the piezomagnetic waveguide is considered. The model is comprised of piezomagnetic layer lying on a lossy viscoelastic substrate. In this regard a direct Sturm–Liouville problem has been formulated and solved. Complex dispersion equations have been derived for both magnetically open and short cases. For each case we have obtained two nonlinear equations containing two unknowns and various parameters. These nonlinear equations are solved using suitable numerical method implemented in Mathematica 9.0 software. Further, the obtained frequency relations are matched with the classical case of Love wave to validate the problem. The influence of different parameters (thickness of the layer, frequency, piezomagnetic coefficient and elastic parameter) on the phase velocity and attenuation of Love-type waves are discussed and delineated through graphs. The results have immense applications in non-destructive evaluation, designing of viscosity sensors, SAW devices, biosensors and chemosensors.
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Effect of temperature on the transmission characteristics of high-torque magnetorheological brakesThis paper aims to investigate the effect of temperature on the transmission characteristics of high-torque magnetorheological (MR) brakes by theoretically analyzing a disc brake, the pressure characteristics of the magnetorheological fluid (MRF) in axial, and the heat dissipation of an MR brake. A high-torque squeezing MRF brake with a water cooling method for heat dissipation is designed and a temperature-torque performance experimental system is established to conduct the experiments. The experimental results indicate that the high-torque squeezing MRF brake exhibits workable pressure characteristics. Meanwhile, the braking torque presents a variation trend that is initially increasing then decreasing when the temperature increases from 25 °C to 150 °C. The magnitude of decrease is approximately 210 N m, which decreases from 1800 to 1590 N m. Moreover, the temperature of the MRF presents an almost linear increase at different slip powers and the rate of temperature rise increases with an increase in slip power. The findings of this study prove that an effective cooling method can be vital to the stable operation of the high-torque MR brakes.
Smart materials, called also intelligent or responsive materials,[1][2] are designed materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, moisture, electric or magnetic fields, light, temperature, pH, or chemical compounds. Smart materials are the basis of many applications, including sensors and actuators, or artificial muscles, particularly as electroactive polymers (EAPs).[3][4],[5][6],[7][8]
Terms used to describe smart materials include shape memory material (SMM) and shape memory technology (SMT).[9]
Types[edit]
There are a number of types of smart material, of which are already common. Some examples are as following:
- Piezoelectric materials are materials that produce a voltage when stress is applied. Since this effect also applies in a reverse manner, a voltage across the sample will produce stress within sample. Suitably designed structures made from these materials can, therefore, be made that bend, expand or contract when a voltage is applied.
- Shape-memory alloys and shape-memory polymers are materials in which large deformation can be induced and recovered through temperature changes or stress changes (pseudoelasticity). The shape memory effect results due to respectively martensitic phase change and induced elasticity at higher temperatures.
- Photovoltaic materials or optoelectronics convert light to electrical current.
- Electroactive polymers (EAPs) change their volume by voltage or electric fields.
- Magnetostrictive materials exhibit a change in shape under the influence of magnetic field and also exhibit a change in their magnetization under the influence of mechanical stress.
- Magnetic shape memory alloys are materials that change their shape in response to a significant change in the magnetic field.
- Smart inorganic polymers showing tunable and responsive properties.
- pH-sensitive polymers are materials that change in volume when the pH of the surrounding medium changes.
- Temperature-responsive polymers are materials which undergo changes upon temperature.
- Halochromic materials are commonly used materials that change their color as a result of changing acidity. One suggested application is for paints that can change color to indicate corrosion in the metal underneath them.
- Chromogenic systems change color in response to electrical, optical or thermal changes. These include electrochromic materials, which change their colour or opacity on the application of a voltage (e.g., liquid crystal displays), thermochromic materials change in colour depending on their temperature, and photochromic materials, which change colour in response to light—for example, light-sensitive sunglasses that darken when exposed to bright sunlight.
- Ferrofluids are magnetic fluids (affected by magnets and magnetic fields).
- Photomechanical materials change shape under exposure to light.
- Polycaprolactone (polymorph) can be molded by immersion in hot water.
- Self-healing materials have the intrinsic ability to repair damage due to normal usage, thus expanding the material's lifetime.
- Dielectric elastomers (DEs) are smart material systems which produce large strains (up to 500%) under the influence of an external electric field.
- Magnetocaloric materials are compounds that undergo a reversible change in temperature upon exposure to a changing magnetic field.
- Thermoelectric materials are used to build devices that convert temperature differences into electricity and vice versa.
- Chemoresponsive materials change size or volume under the influence of external chemical or biological compound.[10]
Smart materials have properties that react to changes in their environment. This means that one of their properties can be changed by an external condition, such as temperature, light, pressure, electricity, voltage, pH, or chemical compounds. This change is reversible and can be repeated many times.There is a wide range of different smart materials. Each offer different properties that can be changed. Some materials are very good indeed and cover a huge range of the scales.
See also[edit]
References[edit]
- ^Smart Materials Book Series Royal Society of Chemistry , Cambridge UK, http://pubs.rsc.org/bookshop/collections/series?issn=2046-0066
- ^Materials that Move: Smart Materials, Intelligent Design M. Bengisu , M. Ferrara Springer 2018 ISBN9783319768885https://www.springer.com/de/book/9783319768885
- ^M.Shahinpoor and H.-J. Schneider, Eds. Intelligent Materials; Royal Society of Chemistry, Cambridge UK, 2007.http://pubs.rsc.org/en/Content/eBook/978-0-85404-335-4
- ^Encyclopedia of Smart Materials Wiley 2002 https://onlinelibrary.wiley.com/doi/book/10.1002/0471216275
- ^Supramolecular Soft Matter: Applications in Materials and Organic Electronics Takashi Nakanishi, Ed,.Wiley 2011, https://onlinelibrary.wiley.com/doi/book/10.1002/9781118095331
- ^P Gaudenzi Smart Structures: Physical Behavior, Mathematical Modeling and Applications, Wiley-Blackwell; 2009
- ^H. Janocha Adaptronics and Smart Structures: Basics, Materials, Design, and Applications Reprint Springer 2010
- ^M. Schwartz, Ed. Smart Materials, CRC Press Boca Raton 2008,https://www.crcpress.com/Smart-Materials/Schwartz/p/book/9781420043723
- ^Mohd Jani, Jaronie; Leary, Martin; Subic, Aleksandar; Gibson, Mark A. (April 2014). 'A review of shape memory alloy research, applications and opportunities'. Materials & Design. 56: 1078–1113. doi:10.1016/j.matdes.2013.11.084.
- ^Chemoresponsive Materials /Stimulation by Chemical and Biological Signals, Schneider, H.-J. ; Ed:, (2015)The Royal Society of Chemistry, Cambridge https://dx.doi.org/10.1039/97817828822420
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