Showing papers in "Smart Materials and Structures in 2020"

Review on the use of piezoelectric materials for active vibration, noise, and flow control

Abstract: Considering the number of applications, and the quantity of research conducted over the past few decades, it wouldn't be an overstatement to label the piezoelectric materials as the cream of the crop of the smart materials. Among the various smart materials, the piezoelectric materials have emerged as the most researched material for practical applications. They owe it to a few key factors like low cost, large frequency bandwidth of operation, availability in many forms, and the simplicity offered in handling and implementation. For piezoelectric materials, from an application standpoint, the area of active control of vibration, noise, and flow, stands, alongside energy harvesting, as the most researched field. Over the past three decades, several authors have used piezoelectric materials as sensors and actuators, to (i) actively control structural vibrations, noise and aeroelastic flutter, (ii) actively reduce buffeting, and (iii) regulate the separation of flows. These studies are spread over several engineering disciplines-starting from large space structures, to civil structures, to helicopters and airplanes, to computer hard disk drives. This review is an attempt to concise the progress made in all these fields by exclusively highlighting the application of the piezoelectric material. The research carried out in the past five years, in the areas of modeling, and optimal positioning of piezoelectric actuators/sensors, for active vibration control, are covered. Along with this, investigations into different control algorithms, for the piezoelectric based active vibration control, are also reviewed. Studies reporting the use of piezoelectric modal filtering and self sensing actuators, for active vibration control, are also surveyed. Additionally, research on semi-active vibration control techniques like the synchronized switched damping (on elements like resistor, inductor, voltage source, negative capacitor) has also been covered

Maximum power point of piezoelectric energy harvesters: a review of optimality condition for electrical tuning

Abstract: This paper is a review and synthetic overlook of existing energy harvesting circuits and techniques for piezoelectric energy scavengers. We provide a hierarchical presentation based on functional analysis to distinguish between existing solutions which may look superficially similar but prove to perform very differently in practice. Based on this hierarchical presentation, definitions of topologies, architectures and techniques are given in order to avoid redundancy among existing and future solutions. Then, after a thorough and unified mathematical analysis of the general problem to address, we present a comparison of the conditions for each technique to maximize the power flow from an external vibration source to an electrical load. This analysis is meant to help researchers and engineers make optimal choices for effective implementation of Maximum Power Point Tracking (MPPT).

Scavenging vibrational energy with a novel bistable electromagnetic energy harvester

Abstract: Harvesting energy from mechanical vibrations via nonlinear energy harvesters has been considered as an effective approach for permanently powering embedded devices and sensors. Many previous studies focused on nonlinear piezoelectric energy harvesters based on cantilever beam structures. This paper presents a novel bistable electromagnetic energy harvester (BEEH) with several permanent magnets (PMs). The bistability is achieved by designing the interaction between magnetic repulsive and attractive forces. The shape of potential wells can be changed by adjusting the distance among the PMs. The theoretical model of the BEEH is established and the analytical solutions are obtained by using the harmonic balance method (HBM). The effects of the excitation frequency, excitation amplitude, resistance and shape of potential wells on the energy harvesting performance of the BEEH are investigated numerically and experimentally. The results show that the proposed BEEH has a wide operating bandwidth and high energy harvesting efficiency. The output power can reach up to 28 mW, which is able to power up some low-power consumption devices.

Shape memory alloy (SMA)-cable-controlled sliding bearings: development, testing, and system behavior

Abstract: This paper presents an innovative type of friction sliding bearing system incorporating shape memory alloy (SMA) cables. The study commences with cyclic tests on individual SMA cables to understand their fundamental mechanical properties. The working principle of the proposed SMA-cable-controlled friction sliding bearing (SMA-sliding bearing) is subsequently described, followed by physical tests on two SMA-sliding bearing specimens. The bearing specimens show rectangular hysteresis loops induced by Coulomb friction before the SMA cables are stretched, and afterward the load resistance and energy dissipation capacity of the bearings are increased accompanied by certain self-centering capability due to the engagement of the SMA cables. Such action is expected to effectively restrict excessive displacements of the bearings and to help reduce the residual displacement. Following the experimental study, a theoretical model of the new bearing is developed and numerical simulation is carried out. The theoretical and numerical results agree very well with the experimental results. A case study focusing on a three-span continuous bridge subjected to pulse-like near-fault (NF) ground motions is subsequently conducted, where three types of bearing system, namely, conventional sliding bearing system, SMA-sliding bearing system, and steel-cable-controlled (steel-sliding) bearing system are compared. The system-level analysis results show that the proposed SMA-sliding bearing has its superiority in superstructure displacement control, with a limited increase in the curvature ductility of the pier.

Novel multidirectional negative stiffness mechanical metamaterials

Abstract: This paper presents a novel tri-directional negative stiffness (NS) mechanical metamaterial, consisting of disk structure elements arranged in three-dimensions. The NS behavior was achieved through the elastic instability of the disk structure. Through the combination of numerical simulations and experiments, the NS property, the deformation mechanisms, and the basic mechanical performance of the disk structure and the novel NS mechanical metamaterial were systematically investigated. The influence of the geometric parameters on the snap-through behaviors of the NS metamaterial was investigated through the experimentally verified numerical method, and further designs were conducted on the disk structure to tailor its mechanical responses. Also based on the instability of the disk structure, several novel multidirectional NS structures, which can achieve NS behavior along five and seven loading directions, were firstly proposed. This innovation improves the homogeneity of the NS metamaterials, and is expected to expand the application scope of such metamaterial, considering that the previous reported NS metamaterial can exhibit NS behavior along three-dimensions at most. Moreover, the mechanical performance of the proposed NS metamaterial is tunable, benefited from the special structure form of itself. To our knowledge, this work is first to design NS metamaterial using the disk structures, and report the multidirectional (more than tri-directions) NS metamaterials.

A novel 3D re-entrant unit cell structure with negative Poisson’s ratio and tunable stiffness

Abstract: In this paper, a novel three-dimensional (3D) unit cell structure with butterfly-like perforations was designed, and negative Poisson's ratio and tunable stiffness were achieved in such a geometry. The Poisson's ratio and strain-stress relationship of structures with different geometric parameters were determined using the finite element method (FEM). Samples with identical geometric variables to those of finite element models were fabricated via 3D printing technique, and their Poisson's ratios and stress–strain relationships were experimentally determined and compared with the FEM results. Results showed that the proposed 3D cellular structures exhibit negative Poisson's ratios, and a minimal value of −0.7091 could be reached. The stress–strain curve of each structure exhibited three distinct stages (elastic response, rib buckling and self-contact), with different elastic moduli being observed at each stage, and demonstrated a tunable range of the compressive stiffness ratio between stages varying from 0.1866 to 1.4006(tunable stiffness), as determined by FEM analysis. Good agreement was found between the experimental results and FEM predictions. The design concept can be implemented and optimized for specific applications via geometric parameters manipulation.

Poly-Saora robotic jellyfish: swimming underwater by twisted and coiled polymer actuators

Abstract: Jellyfish are energy-efficient swimmers due to the muscle-powered flapping of their soft bell that facilitates a unique energy recapture mechanism. In this paper, we present a bio-inspired jellyfish robot named Poly-Saora that mimics the swimming behavior of the jellyfish species Black sea nettle (Chrysaora achlyos). An assembly-based fabrication method is used to create the Poly-Saora that is developed mainly with polymeric materials (95% of the robot by volume). Twisted and coiled polymer (TCP) actuators are successfully implemented in this robot and show great potential for underwater applications. The influence of different parameters such as the amplitude of the input power, the actuation frequency, and the lifecycle of the actuator are investigated underwater. A full characterization of 6-ply TCP muscles is demonstrated. An actuation strain of ~10 % is achieved in water at a frequency of 0.1Hz and 50 kPa load. When integrated into the jellyfish, the TCP was able to bend a single bell by 17˚. Poly-Saora was able to swim a vertical distance of 180 mm in 220 s with four TCP actuators each confined in a separate conduit. The robot mimics the swimming behavior of a real jellyfish by contracting the bell segments through the activation of the actuators, which generates forced water circulation under the bell in a pulsating rhythm, consequently creating a vertical movement of the robot. Overall, Poly-Saora is presenting a model of an underwater system that is driven by stimuli-responsive polymer materials and has unique advantages over conventional rigid robots due to their lightweight, muscle-like structures, silent actuation and ease of manufacturing. This robot can be used for safe interaction with other underwater species and their natural habitats when fully developed.

A soft gripper with programmable effective length, tactile and curvature sensory feedback

Abstract: Soft grippers based on fluidic elastomer actuators have the characteristics of gentle and adaptable grasping that is difficult to realize by rigid grippers. However, it remains challenging to implement a compact gripping device that has multiple bending configurations to exert appropriate force, and sensory capabilities to evaluate the grasping state. Here, we present a soft gripper with variable effective lengths (VELs) that is achieved by rapidly softening selective shape memory polymer sections (within 0.6 s) via a flexible heater. A vortex tube is used to jet cold airflow to accelerate the stiffening process (within 14 s). We show that the soft gripper can not only identify objects but also exert higher gripping force by setting appropriate length according to pneumatic-thermal hybrid actuation. We further propose a touch-reconfiguration-grasp strategy to showcase the synergy of VELs and sensory feedback. The gripper first touches the object under the fully softened state and evaluates the grasping condition based on the sensors' feedback, then reconfigures the bending length and grasps the object until successful. We envision that soft grippers with sensing ability and reconfigurable grasping configurations would be promising for future applications in unconstructed environments.

Flexible and wearable sensor based on graphene nanocomposite hydrogels

Abstract: Flexible and wearable sensor based on nanocomposite hydrogels has been proposed for monitoring the human large-scale, small-scale movements and several physiological signals. The nanocomposite hydrogel, prepared from graphene oxide (GO), polyvinyl alcohol (PVA) and polydopamine (PDA), exhibits excellent mechanical and electrical properties with tensile stress of 146.5 KPa, fracture strain of 2 580 %, fracture energy of 2 390.86 KJ m¬¬-3, and the conductivity of 5 mS cm-1. In addition, it possesses other merits including good self-healing with the electrical self-healing efficiency of 98 % of its original resistance within 10 seconds, and strong self-adhesion onto a variety of surfaces of materials. This self-adhesive, self-healing, graphene-based conductive hydrogel can further assembled as wearable sensors to accurate and real-time detect the signals of human large-scale motions (including bending and stretching fingers joints, wrists joints, elbows joints, neck joints and knees joints) and small-scale motions (including swallowing, breathing and pulsing) through fracturing and recombination of reduced graphene oxide (rGO) electrical pathways in porous structures of hydrogel networks. Furthermore, the hydrogel can also be used as self-adhesive surface electrodes to detect human electrophysiological (ECG) signals. Therefore, the hydrogel-based wearable sensor is expected to be used for long-term and continuous monitoring human body motion and detecting physiological parameters.

Structural response monitoring of concrete beam under flexural loading using smart carbon black/cement-based sensors

Abstract: The fractional changes of resistivity (FCR) of cement-based sensors with various carbon black (CB) contents were firstly studied under uniaxial compression in this study. Then the piezoresistive behaviours of embedded cement-based sensors in unreinforced small-scale concrete beams were investigated under flexural bending load. As for the embedded cement-based sensors in the compression zones of the beam, the stress magnitude and crack failure initiation of the beams can be detected by a gradual decrease and then a sharp increase in the FRC. On the other hand, as for the counterpart sensors in the tension zones of the beam, the stress magnitude and crack failure initiation can be recognized by the gradual increase in resistivity and then a rapid jump in the FRC. During the stress monitoring of the concrete beam, it is found that the FCR values of cement-based sensors in both the compression and tension zones were consistent with the flexural stress changes, which exhibit acceptable sensitivity and reversibility. It is observed that the very firm and dense interfaces in the boundaries indicate the excellent cohesion between embedded CB/cement-based sensors and beams. The related results demonstrate that the CB/cement-based sensors embedded in concrete demonstrate excellent piezoresistive behaviours to potentially monitor the stress magnitude and failure process of concrete infrastructures.

Programmable metamaterials with digital synthetic impedance circuits for vibration control

Abstract: This paper studies a new type of smart metamaterial consisting of piezoelectric actuators and digital synthetic impedance circuits (digital circuits). The digital circuit contains a micro-controller. By programming the micro-controller, the circuit can establish any desired impedance between the terminals of the connected piezoelectric patch, therefore to program the dynamical behaviors of the designed metamaterial. In this sense, a programmable metamaterial is studied. Experiments are conducted to study its programmable dynamical behaviors, with a particular focus on vibration reduction. Numerical simulations are also done in this work to qualitatively verify the experimental results. Different design methods are used to customize the dynamical behaviors of the designed metamaterial. Results demonstrate that the proposed smart metamaterial can be flexibly programmed online to reduce vibration at desired frequencies or within a large frequency band. The proposed programmable metamaterial conception can be naturally extended to other kinds of structures like plates and shells, they are promising components in the future adaptive structures.

Piezoelectric wind energy harvesting subjected to the conjunction of vortex-induced vibration and galloping: comprehensive parametric study and optimization

Abstract: This study performs a comprehensive parametric study and optimization of a piezoelectric wind energy harvester subjected to the conjunction of vortex-induced vibration (VIV) and galloping. The mathematical model of the harvester undergoing both the VIV and galloping is formulated, which is experimentally validated through the wind tunnel tests. The experimental results uncover that different combinations of the aerodynamic parameters of the model significantly influence the system dynamic behaviors. Changing the bluff body's cross-section shape can alter the aerodynamic parameters. In the experiment, a unique hump phenomenon due to the coupled VIV and galloping is discovered, which significantly improves the voltage output. The influence of each aerodynamic parameter on the system performance is revealed, and the aerodynamic parameter's effect is also mathematically interpreted by the terms in the governing equations. Finally, this study presents an effective structural optimization method based on the genetic algorithm (GA) to seek the optimal structural natural frequency matching up the given aerodynamic parameters. Results show that the piezoelectric wind energy harvester with the optimal designed natural frequency outperforms the harvester with other values, and the performance is also robust against a certain range of the parametric uncertainties.

A review on shape memory alloy reinforced polymer composite materials and structures

Abstract: Imparting controllable flexural rigidity into a material system is one of the key motivations for the design of intelligent materials for structural applications. In this direction, shape memory alloy (SMA) reinforced polymer composites have enormous potentials for active shape and vibration control of systems related to aerospace, automobile, and energy harvesting applications. The primary motivation of reinforcing SMA wires into a composite is to actively change the composite stiffness or elasticity through thermo-mechanical as well as electrical/magnetic stimulation. The SMA-reinforced hybrid composites are found to be able to adapt their shape, which may also improve the specific strength, vibration damping, and self-healing capability by utilizing shape memory effect and pseudoelastic behavior of the SMA. In this paper, we intend to provide a comprehensive review of all SMA-reinforced composites available today in the open literature and a critical assessment of the technology. Currently, shape memory alloys in the form of long fibers (wires), ribbons, short fibers, and particles are used for hybridizing the reinforcements in composites. Continuous SMA fiber embedded composites are generally used for shape control of structures. However, it has difficulty in obtaining suitable interfacial characteristics required for actuation. The discontinuous SMA embedded composites have scope for modifying such active properties. The work presented here gives an overview of the concepts of design, development, and modeling of continuous and discontinuous shape memory alloy embedded composites for advanced smart composites.

Origami-inspired self-deployment 4D printed honeycomb sandwich structure with large shape transformation

Abstract: 4D printing provides more design freedom for the static structures by adding time dimension in 3D printing. In recent years, some types of active origami structures fabricated by 4D printing have been developed, but most of these structures were thin sheets, which may lead to poor mechanical properties of the structures. In this work, honeycomb sandwich structures were designed to improve the stiffness and recovery force of origami structures. The in-plane tension, in-/out-plane three-point bending, recovery force and shape memory performances of the sandwich structures were investigated. The shape fixity and shape recovery ratio of the active sandwich structures were 98% and 99%, indicating excellent shape memory performance. The application of the sandwich structures in thermally activated self-deployment origami structures was verified. These developed origami structures have the advantages of large area change ratio and fast response speed, demonstrating the great application prospects in the space deployable structures such as antennas.

Deterministic snap-through buckling and energy trapping in axially-loaded notched strips for compliant building blocks

Abstract: Harnessing elastic instabilities has enabled recent advances in new classes of materials and devices due to the characteristics of amplifying force and augmented motion. Achieving these enhanced effects usually relies on using buckled beam or strips as the building block. In response to such a need, we investigate the contact-induced energy trapping of axially-loaded strips. To achieve the feature of energy trapping, we implement an "imperfection by design" approach to trigger a controllable and predictable interactive buckling in axially-loaded strips. By combining finite-element simulations and desktop-scale experiments, we found that the contact of strip elements can be induced by strategically controlled the number, the location and the layout of local predefined geometric defects, leading to a deterministic on-demand snap-through buckling response compared to the ones without such geometric defects. Our study thereby opens avenues for the design of the next generation of compliant mechanisms with high fidelity and low sensitivity over a wide range of length scales.