Showing papers in "Smart Materials and Structures in 2019"

A review of energy harvesting using piezoelectric materials: state-of-the-art a decade later (2008–2018)

Abstract: Energy harvesting technologies have been explored by researchers for more than two decades as an alternative to conventional power sources (e.g. batteries) for small-sized and low-power electronic devices. The limited life-time and necessity for periodic recharging or replacement of batteries has been a consistent issue in portable, remote, and implantable devices. Ambient energy can usually be found in the form of solar energy, thermal energy, and vibration energy. Amongst these energy sources, vibration energy presents a persistent presence in nature and manmade structures. Various materials and transduction mechanisms have the ability to convert vibratory energy to useful electrical energy, such as piezoelectric, electromagnetic, and electrostatic generators. Piezoelectric transducers, with their inherent electromechanical coupling and high power density compared to electromagnetic and electrostatic transducers, have been widely explored to generate power from vibration energy sources. A topical review of piezoelectric energy harvesting methods was carried out and published in this journal by the authors in 2007. Since 2007, countless researchers have introduced novel materials, transduction mechanisms, electrical circuits, and analytical models to improve various aspects of piezoelectric energy harvesting devices. Additionally, many researchers have also reported novel applications of piezoelectric energy harvesting technology in the past decade. While the body of literature in the field of piezoelectric energy harvesting has grown significantly since 2007, this paper presents an update to the authors' previous review paper by summarizing the notable developments in the field of piezoelectric energy harvesting through the past decade.

4D printed tunable mechanical metamaterials with shape memory operations

Abstract: The aim of this paper is to introduce tunable continuous-stable metamaterials with reversible thermomechanical memory operations by four-dimensional (4D) printing technology. They are developed based on an understanding on glassy-rubbery behaviors of shape memory polymers and hot/cold programming derived from experiments and theory. Fused decomposition modeling as a well-known 3D printing technology is implemented to fabricate mechanical metamaterials. They are experimentally tested revealing elastic-plastic and hyper-elastic behaviors in low and high temperatures at a large deformation range. A computational design tool is developed by implementing a 3D phenomenological constitutive model coupled with a geometrically non-linear finite element method. Governing equations are then solved by an elastic-predictor plastic-corrector return map procedure along with the Newton-Raphson and Riks techniques to trace non-linear equilibrium path. A tunable reversible mechanical metamaterial unit with bistable memory operations is printed and tested experimentally and numerically. By a combination of cold and hot programming, the unit shows potential applications in mimicking electronic memory devices like tactile displays and designing surface adaptive structures. Another design of the unit shows potentials to serve in designing self-deployable bio-medical stents. Experiments are also conducted to demonstrate potential applications of cold programming for introducing recoverable rolling-up chiral metamaterials and load-resistance supportive auxetics.

Percussion-based bolt looseness monitoring using intrinsic multiscale entropy analysis and BP neural network

Abstract: In this paper, a novel percussion-based bolt looseness monitoring approach using intrinsic multiscale entropy analysis and back propagation (BP) neural network is proposed. The percussion-caused audio signals of bolt connection are decomposed by complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) to obtain intrinsic mode functions (IMFs). The IMFs are in order of the high-to-low instantaneous frequencies and contain underlying dynamical characteristic information of audio signals. The multiscale sample entropy (MSE) is improved by smoothed coarse graining process, and the proposed improved multiscale sample entropy (IMSE) values of certain IMFs can be adopted as indicators of different bolt looseness conditions. The intrinsic multiscale entropy analysis consisting of CEEDMAN and IMSE can properly extract underlying dynamical characteristic information during audio signal processing in bolt looseness condition identification. The obtained indicators, which are IMSE values at smallest scale factors, were employed as input in BP neural network for training and testing, to achieve accurate and stable bolt looseness condition monitoring. The effectiveness and superiority of the proposed approach has been validated by theoretical derivation and practical experimental researches, and the adaptivity and robustness of the proposed approach are also illustrated. The results of the researches demonstrate the proposed approach is promising in practical applications of bolt looseness monitoring.

Machine-learning based design of active composite structures for 4D printing

Abstract: Active composites are a class of materials that have environmentally responsive components within them. One key advantage of active composites is that through mechanics design, a variety of actuation can be achieved. The development of active composites has been significantly enhanced in recent years by multimaterial 3D printing where different materials can be precisely placed in 3D space, enabling the achievement of shape-shifting of 3D printed parts, or 4D printing. In practical applications, it is highly desirable that the part shape can change in a pre-described manner, which requires the careful design of where to place different materials. However, designing an active composite structure to achieve a target shape change is challenging because it requires solving an inverse problem with spatially heterogenous, highly nonlinear (active) material behavior within a potentially complex boundary value problem. In this paper we present a machine learning approach to the design of active composite structures that can achieve target shape shifting responses. Our strategy is to combine the finite element method with an evolutionary algorithm. In order to achieve a target shape, we compose the structures of equally sized voxel units that are made of either a passive or an active material and optimize the distribution of these two material phases. The optimization method is tested against several illustrative examples in active composite design to show the agreement between the target shape and the best machine learning solution obtained.

A cross-coupled dual-beam for multi-directional energy harvesting from vortex induced vibrations

Abstract: This study proposes a cross-coupled dual-beam structure for energy harvesting from vortexinduced vibrations (VIV) induced by wind flows in different directions. A series of wind tunnel tests are conducted to investigate the performance of the proposed energy harvester subjected to the wind load with various speeds and directions. The upper and bottom piezoelectric beams can generate a maximum power output of 6.77 μW and 56.64 μW, respectively. The dominant operation frequencies in different directions are different which indicates a potential broadband capability. A parametric study is performed to reveal the effect of the dimension of the bluff body on the performance of the proposed energy harvester.

Active metamaterials with broadband controllable stiffness for tunable band gaps and non-reciprocal wave propagation

Abstract: One dimensional active metamaterials with broadband controllable bending stiffness are studied in this paper. The key unit of the active metamaterials is composed of a host beam and piezoelectric patches bonded on the beam surfaces. These patches serve as sensors or actuators. An appropriate feedback control law is proposed in order to change the bending stiffness of the active unit. The input of the control law is the voltage on the sensors, the output is the voltage applied on the actuators. Due to the control, bending stiffness of the active unit is (1 + α) times of that of the bare host beam, α being a design parameter in the control law. The bending stiffness can be tuned to desired value by changing α. The performances of the controlled bending stiffness are analytically and numerically studied, the stability issues are also discussed. The active units are first used in a spatial periodic waveguide to have tunable band gaps, then they are integrated in a spatiotemporal periodic waveguide to realize non-reciprocal wave propagation. Performances of the two waveguides are numerically studied.

Aerospace-grade surface mounted optical fibre strain sensor for structural health monitoring on composite structures evaluated against in-flight conditions

Abstract: Optical fibre sensors are being investigated since many years as candidates of choice for supporting structural health monitoring (SHM) in aerospace applications. Fibre Bragg grating (FBG) sensors, more specifically, can provide for accurate strain measurements and therefore return useful data about the mechanical strain state of the structure to which they are attached. This functionality can serve the detection of damage in an aircraft structure. However, very few solutions for protecting and bonding optical fibres to a state-of-the-art aircraft composite material have been reported. Most proof-of-principle demonstrations using optical fibre sensors for aerospace SHM-related applications reported in literature indeed rely on unpackaged fibre sensors bonded to isotropic metallic surfaces in a mostly unspecified manner. Neither the operation of the sensor, nor the adhesive material and bonding procedure are tested for their endurance against a full set of standardized in-flight conditions. In this work we propose a specialty coated FBG sensor and its permanent installation on aerospace-grade composite materials, and we demonstrate the compatibility with aerospace in-flight conditions. To do so we thoroughly evaluate the quality of the operation of the FBG sensor by correlating the reflection spectra of the installed sensors before and after exposure to a full set of realistic in-flight conditions. We also evaluate the difference in strain measured by the FBG, since any damage in the adhesive bond line would lead to strain release. The applied test conditions are based on aerospace standards and include temperature cycling, pressure cycling, exposure to humidity and Smart Materials and Structures Smart Mater. Struct. 28 (2019) 065008 (13pp) https://doi.org/10.1088/1361-665X/ab1458 Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. 0964-1726/19/065008+13$33.00 © 2019 IOP Publishing Ltd Printed in the UK 1 hydraulic fluid and fatigue loading. We show that both the bond line and the quality of the sensor signal were negligibly affected by the applied environmental and mechanical loads representing in-flight conditions and therefore conclude that it can be considered for SHM of aerospace-grade composite materials.

Elastic Shape Morphing of Ultralight Structures by Programmable Assembly.

Abstract: Ultralight 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 (5.6mgcm3 ). 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 4.27m 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.

Untethered soft robotic jellyfish

Abstract: Inspired by natural creatures, soft robots possess the unique advantages of large actuation and excellent adaptability. Untethered designs of soft robots are drawing more attention to researchers, but current research is limited. Also, there is an increasing need to improve the performance of bio-mimetic robots. This work describes an untethered soft robotic jellyfish with high mobility that can mimic a natural jellyfish's performance. The electrode of the robotic jellyfish is made by sandwiching carbon grease between two layers of dielectric elastomer film. The frame of the material, where six plastic paddles are attached, is made from a silicone elastomer. The robotic jellyfish has a maximum recorded swim speed of up to 1 cm s -1 , with a peak thrust force of 0.000 12 N. A finite element simulation is developed to study the performance of the robotic jellyfish in a theoretical manner. By embedding a compact remote-controlled power source, the robotic jellyfish is made autonomous. In this case, the max peak speed is around 0.5 cm s -1 . Ultimately, the working principles of the bio-mimetic robotic jellyfish can be useful in field studies and to guide the design of soft robots and flexible devices.

Bolt preload measurement based on the acoustoelastic effect using smart piezoelectric bolt

Abstract: Precise 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.

Perspective of additive manufacturing for metamaterials development

Abstract: Metamaterials are featured by artificial composite structures with exotic properties, which process promising application potentials in various areas. However, the manufacturing of metamaterials faces great challenges due to the structural complexity, accuracy requirement, and small scale. Additive manufacturing (AM), as a layer-by-layer technique, shows intrinsic advantages in the fabrication of metamaterials. This paper extensively reviews the current state on how and to what extent AM techniques are adopted for metamaterials fabrication, in which the metamaterials are mainly classified into mechanical, acoustic and electromagnetic types. More importantly, the challenges and research opportunities are discussed for AM fabrication of metamaterials, with focus on high precision, multi-structural and multi-material, topology optimization, support structure, anisotropy and heterogeneity, residual stresses and application realization. It is expected that with further innovative solutions being developed to bridge the research gaps, the industries will become more confident to adopt metamaterials in devices and systems for critical applications.

A smart harvester for capturing energy from human ankle dorsiflexion with reduced user effort

Abstract: Scavenging energy from human motion is a potential way to meet the increasing requirement of electrical power supply for portable electronics. However, since the conventional energy harvesters may collect both positive and negative work, the users have to pay extra efforts. This work aims at developing a smart energy harvester to accurately identify and capture the negative work of human ankle motion. During normal walking, only the dorsiflexion at stance phase performs negative work. Thus, one-way clutch is employed to filter ankle plantarflexion and mechanical contact switch array is used to disconnect electrical load, avoiding capturing positive work when ankle dorsiflexion is at swing phase. With the one-way clutch and mechanical contact switch array, the energy harvester can effectively target negative work as energy scavenged without consuming electrical energy. A wearable and light prototype is built to test its power output and users' metabolic expenditure during walking. The energy harvesting system is also modeled and analyzed. The experimental results show that the energy harvester produces an average power of 0.35 W at 4.9 km h−1 while reducing metabolic expenditure by 0.84 W, so as to achieve lower cost of harvesting compared with the previous work.

Additive manufacture of multistable structures

Abstract: Residual thermal stresses which develop during additive manufacturing processes are often a cause of unwanted component deformation and mechanical failure. We demonstrate that this impairment can in fact be exploited to enhance the design process for shell structures, where bistability is known to emerge in particular instances due to the presence of inelastic stresses. Multistable structures are produced through a single additive manufacturing operation by considering the inherent availability of thermal stresses in certain additive technologies. This concept is demonstrated through an analytical example, numerical simulations and a physical demonstrator produced via selective laser sintering of a titanium alloy. Our findings underline these hitherto untapped capabilities of additive processes and facilitate a deeper understanding of the thermal stresses developed during manufacture.

Design of a disk-swing driven piezoelectric energy harvester for slow rotary system application

Abstract: This paper presents mathematical modelling of an energy harvester that converts slow mechanical rotation into piezoelectric vibration using a small disk and a pair of magnets, for large-scale machinery monitoring applications such as wind turbine blades The harvester consists of a piezoelectric cantilevered beam, a gravity-induced disk, and magnets attached to both the beam and the disk The energy method is used to derive the three coupled equations that describe the motion of the disk, the vibration of the beam, and the harvester voltage output The equations are solved using ODE45 in MATLAB software and verified by the corresponding experimental study The result shows varied energy harvesting performance by blade rotational speed At low blade speed, the harvester generates power by regularized magnetic excitation per blade revolution At high blade speed, however, the disk behavior becomes chaotic to increase excitation force and power generation The results show that the model can quantify power as a function of blade speed, and the proposed harvester can generate a considerable amount of power for self-sustainable sensing and monitoring of wind turbine blades

A general soft robot module driven by twisted and coiled actuators

Abstract: Soft robots usually have soft structures and multiple degrees of freedom, and they are capable of large deformations and safe human–machine interactions. But unlike rigid robots which can be easily assembled from multitudinous general components, the fabrications of soft robots are more difficult. This work presents a general soft robot module that can be assembled into a great variety of soft robots. This module can bend in any direction and the bending angle can be controlled easily and accurately; it has a bar-like soft body made from silicone, and the bending deformation is actuated by multiple twisted and coiled actuators (TCAs) that are uniformly distributed around the soft body. The cost of the module is very low since the silicone is very cheap and TCAs are also very cheap as that they can be easily fabricated from polymer fibers such as fishing lines and sewing threads. A prototype was made, and an angle control system was established to control the bending posture of the module precisely. To verify the versatility of the module, a two-finger soft manipulator assembled by the module was made and its grabbing ability was tested.

Effect of temperature on rheological properties of lithium-based magnetorheological grease

Abstract: Huixing Wang1, Yancheng Li2,3, Guang Zhang1, Jiong Wang1 1. School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, People’s Republic of China 2. School of Civil and Environmental Engineering, University of Technology Sydney, Ultimo 2007, Australia 3. College of Civil Engineering, Nanjing Tech University, Nanjing 211800, People’s Republic of China Corresponding author: wjiongz@njust.edu.cn; yancheng.li@uts.edu.au Abstract This paper investigates the impact of temperature on the rheological properties of magnetorheological (MR) grease containing carbonyl iron suspended in lithium-based grease within the temperature range from 10°C to 70°Cunder influence of temperature, i.e. from 10°C to 70°C. Lithium-based MR grease with 70% weight fraction of carbonyl iron has beenis firstly prepared by mechanical mixing. The apparent viscosity and shear stress as a function of shear rate under different temperatures and magnetic field strengths are measured and discussed. It is found that the influence of temperature on apparent viscosity is reducingreduces with the increase of magnetic field strength. In addition, in the presence of magnetic field, maximum yield stress gets demonstrates an increase as temperature increases from 50°C to 60°C. The dynamic properties of MR grease are obtained under oscillatory shear test. The influences of strain amplitude, driving frequency and magnetic field on the dynamic properties of MR grease at different temperature are discussed. The results demonstrate that the enhancement of temperature leads to the increase of storage modulus and the reduction of the loss factor. Microstructural variation of grease matrix at different temperature is proposed as an explanation of the rheological changes of MR grease.

Rheological compatibility of multi-phase shear thickening fluid with a phenomenological model

Abstract: Shear thickening fluid (STF) is a kind of non-Newtonian fluids exhibiting drastic viscosity jump under an increasing shear rate. Even though these fluids are single-phase suspensions including nano-sized particles in a carrier liquid, various additives have been included in the suspensions to form multi-phase shear thickening concept. Despite novel concepts in compositions, rheological models have been studied only for single-phase STFs until this time. In the present work, multi-phase suspensions were fabricated adding aluminum oxide particles in a nano-silica/PEG based STF. Additive amount and temperature were selected as variables in the rheological measurements. Upon obtaining experimental data from the rheological tests, viscosity curves of the multi-phase STFs were adapted for a phenomenological model which was suggested for single-phase STFs. According to the results, the model gave proper fitting for the flow curves beyond the thickening point. However, it yielded a lower performance to predict the shear thinning region prior to the thickening onset. Therefore, a modified model was developed to fully cover the rheological behavior of multi-phase STFs. By the modified model proposed in this study, flow prediction of multi-phase STFs was improved due to the enhanced fitting performance, especially in the shear thinning region.

Soft-smart robotic end effectors with sensing, actuation, and gripping capabilities

Abstract: Soft 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.

Influence of fused deposition modeling process parameters on the transformation of 4D printed morphing structures

Abstract: 4D printing combines additive layer manufacturing processes with smart materials to create structures that are able to change shape or properties over time under the influence of environmental stimuli. The article presents 3D printed multi-material shape-variable structures imitating a hinge. Fused deposition modelling was used because it provides the ability to preprogram structures during the printing process by varying printing parameters. The structures are printed with PLA and TPU and remain flat after printing until they are exposed to a stimulus - heat. The main objective of this article is to present the possibilities of the aforementioned preprogramming step which can be adapted by varying the printing process and design parameters of the printed part. Experimental results are presented investigating the influence of printing speed, temperature of the build plate and number of active layers in the structure. Furthermore, the repeatability of deformations after a small number of cycles is investigated. The obtained results prove that the deformation of the structures can be controlled by printing parameters and a variety of bending degrees can be obtained by manipulating them. Hot water is used as a stimulus in the study to activate the structures but it is believed that other direct and indirect heating sources are also applicable. The research could help predict the behaviour of deformation of shape-morphing structures by selecting certain printing and design parameter values.