In the last 30 days

• Open/close A flexible piezoelectric force sensor based on PVDF fabrics

  Y R Wang et al 2011 Smart Mater. Struct. 20 045009 Tag this article

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  Polyvinylidene fluoride (PVDF) film has been widely investigated as a sensor and transducer material due to its high piezo-, pyro- and ferroelectric properties. To activate these properties, PVDF films require a mechanical treatment, stretching or poling. In this paper, we report on a force sensor based on PVDF fabrics with excellent flexibility and breathability, to be used as a specific human-related sensor. PVDF nanofibrous fabrics were prepared by using an electrospinning unit and characterized by means of scanning electron microscopy (SEM), FTIR spectroscopy and x-ray diffraction. Preliminary force sensors have been fabricated and demonstrated excellent sensitivity and response to external mechanical forces. This implies that promising applications can be made for sensing garment pressure, blood pressure, heartbeat rate, respiration rate and accidental impact on the human body.

• Open/close Hydrogen-fuel-powered bell segments of biomimetic jellyfish

  Yonas Tadesse et al 2012 Smart Mater. Struct. 21 045013 Tag this article

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  Artificial muscles powered by a renewable energy source are desired for joint articulation in bio-inspired autonomous systems. In this study, a robotic underwater vehicle, inspired by jellyfish, was designed to be actuated by a chemical fuel source. The fuel-powered muscles presented in this work comprise nano-platinum catalyst-coated multi-wall carbon nanotube (MWCNT) sheets, wrapped on the surface of nickel–titanium (NiTi) shape memory alloy (SMA). As a mixture of oxygen and hydrogen gases makes contact with the platinum, the resulting exothermic reaction activates the nickel–titanium (NiTi)-based SMA. The MWCNT sheets serve as a support for the platinum particles and enhance the heat transfer due to the high thermal conductivity between the composite and the SMA. A hydrogen and oxygen fuel source could potentially provide higher power density than electrical sources. Several vehicle designs were considered and a peripheral SMA configuration under the robotic bell was chosen as the best arrangement. Constitutive equations combined with thermodynamic modeling were developed to understand the influence of system parameters that affect the overall actuation behavior of the fuel-powered SMA. The model is based on the changes in entropy of the hydrogen and oxygen fuel on the composite actuator within a channel. The specific heat capacity is the dominant factor controlling the width of the strain for various pulse widths of fuel delivery. Both theoretical and experimental strains for different diameter (100 and 150 µm) SMA/MWCNT/Pt fuel-powered muscles with dead weight attached at the end exhibited the highest magnitude under 450 ms of fuel delivery within 1.6 mm diameter conduit size. Fuel-powered bell deformation of 13.5% was found to be comparable to that of electrically powered (29%) and natural jellyfish (42%).

• Open/close Rheological properties of magnetorheological suspensions based on core–shell structured polyaniline-coated carbonyl iron particles

  M Sedlačík et al 2010 Smart Mater. Struct. 19 115008 Tag this article

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  The sedimentation caused by the high density of suspended particles used in magnetorheological fluids is a significant obstacle for their wider application. In the present paper, core–shell structured carbonyl iron–polyaniline particles in silicone oil were used as a magnetorheological suspension with enhanced dispersion stability. Bare carbonyl iron particles were suspended in silicone oil to create model magnetorheological suspensions of different loading. For a magnetorheological suspension of polyaniline-coated particles the results show a decrease in the base viscosity. Moreover, the polyaniline coating has a negligible influence on the MR properties under an external magnetic field B. The change in the viscoelastic properties of magnetorheological suspensions in the small-strain oscillatory shear flow as a function of the strain amplitude, the frequency and the magnetic flux density was also investigated.

• Open/close Application of a PVDF-based stress gauge in determining dynamic stress–strain curves of concrete under impact testing

  Yi Meng and Weijian Yi 2011 Smart Mater. Struct. 20 065004 Tag this article

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  Polyvinylidene fluoride (PVDF) piezoelectric material has been successfully applied in many engineering fields and scientific research. However, it has rarely been used for direct measurement of concrete stresses under impact loading. In this paper, a new PVDF-based stress gauge was developed to measure concrete stresses under impact loading. Calibrated on a split Hopkinson pressure bar (SHPB) with a simple measurement circuit of resistance strain gauges, the PVDF gauge was then used to establish dynamic stress–strain curves of concrete cylinders from a series of axial impact testing on a drop-hammer test facility. Test results show that the stress curves measured by the PVDF-based stress gauges are more stable and cleaner than that of the stress curves calculated with the impact force measured from a load cell.

• Open/close Analytical formulation of optimum material properties for viscoelastic damping

  H H Hilton and Sung Yi 1992 Smart Mater. Struct. 1 113 Tag this article

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  Expressions for stored and dissipated energies in anisotropic viscoelastic bodies are derived using generalized Maxwell models. The relationships between shapes of master relaxation modulus curves and dissipation energy and the latter's influence on passive structural motion control are investigated. The master relaxation modulus curves are analytically generated for parametric variations of initial and relaxed moduli, slopes of the transition region and relaxation time spans. The influences of relaxation modulus shapes and parameters on stored and dissipated energies and on time-dependent deformations under specific loading and environmental conditions are analysed and evaluated. These analytical formulations of 'viscoelastic designer materials' answer questions on how to best manufacture, or select from data banks, materials with optimum properties for specific service requirements including the use of smart viscoelastic damping materials.

• Open/close Mechanics of pressure-adaptive honeycomb and its application to wing morphing

  Roelof Vos and Ron Barrett 2011 Smart Mater. Struct. 20 094010 Tag this article

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  Current, highly active classes of adaptive materials have been considered for use in many different aerospace applications. From adaptive flight control surfaces to wing surfaces, shape-memory alloy (SMA), piezoelectric and electrorheological fluids are making their way into wings, stabilizers and rotor blades. Despite the benefits which can be seen in many classes of aircraft, some profound challenges are ever present, including low power and energy density, high power consumption, high development and installation costs and outright programmatic blockages due to a lack of a materials certification database on FAR 23/25 and 27/29 certified aircraft. Three years ago, a class of adaptive structure was developed to skirt these daunting challenges. This pressure-adaptive honeycomb (PAH) is capable of extremely high performance and is FAA/EASA certifiable because it employs well characterized materials arranged in ways that lend a high level of adaptivity to the structure. This study is centered on laying out the mechanics, analytical models and experimental test data describing this new form of adaptive material. A directionally biased PAH system using an external (spring) force acting on the PAH bending structure was examined. The paper discusses the mechanics of pressure adaptive honeycomb and describes a simple reduced order model that can be used to simplify the geometric model in a finite element environment. The model assumes that a variable stiffness honeycomb results in an overall deformation of the honeycomb. Strains in excess of 50% can be generated through this mechanism without encountering local material (yield) limits. It was also shown that the energy density of pressure-adaptive honeycomb is akin to that of shape-memory alloy, while exhibiting strains that are an order of magnitude greater with an energy efficiency close to 100%. Excellent correlation between theory and experiment is demonstrated in a number of tests. A proof-of-concept wing section test was conducted on a 12% thick wing section representative of a modern commercial aircraft winglet or flight control surface with a 35% PAH trailing edge. It was shown that camber variations in excess of 5% can be generated by a pressure differential of 40 kPa. Results of subsequent wind tunnel test show an increase in lift coefficient of 0.3 at 23 m s ^{− 1} through an angle of attack from − 6° to + 20°.

• Open/close A semi-analytical method and the circumferential dominant modal control of circular cylindrical shells with active constrained layer damping treatment

  Liyun Yuan et al 2010 Smart Mater. Struct. 19 025010 Tag this article

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  To enhance the generality and flexibility of active constrained layer damped (ACLD) forms used in vibration control for circular cylindrical shells, the piezoelectric layer of the ACLD form is divided into several sub-blocks by thin insulated layers, and the sub-blocks are integrated on the viscoelastic layer continuously in the circumferential direction. In addition, on the basis of the authors' recent research on passive constrained layer damped (PCLD) circular cylindrical shells, the piezoelectric effects of the constrained layer (made of piezoelectric material) are further considered. Then, the integrated first-order differential equation for such an ACLD (partially treated in the axial direction) circular cylindrical shell is derived by reformulating the integrated first-order differential equation for the PCLD circular cylindrical shell. Next, employing the extended homogeneous capacity precision integration approach and the superposition principle, a high precision semi-analytical method is developed for solving the dynamic problem for such ACLD circular cylindrical shells. Subsequently, several kinds of circumferential modal control strategy are compared by the method presented. Furthermore, the concept of a circumferential dominant modal control strategy is proposed, which is different from the traditional modal control method. The numerical results show that, on applying the circumferential dominant modal control strategy, the ACLD cylindrical shell attenuates the vibration better. Lastly, some influence factors for the circumferential dominant modal control strategy affecting the damping effect of ACLD circular cylindrical shells are also investigated.

• Open/close A review of power harvesting using piezoelectric materials (2003–2006)

  Steven R Anton and Henry A Sodano 2007 Smart Mater. Struct. 16 R1 Tag this article

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  The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans. Current portable and wireless devices must be designed to include electrochemical batteries as the power source. The use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement. In the case of wireless sensors that are to be placed in remote locations, the sensor must be easily accessible or of a disposable nature to allow the device to function over extended periods of time. Energy scavenging devices are designed to capture the ambient energy surrounding the electronics and convert it into usable electrical energy. The concept of power harvesting works towards developing self-powered devices that do not require replaceable power supplies. A number of sources of harvestable ambient energy exist, including waste heat, vibration, electromagnetic waves, wind, flowing water, and solar energy. While each of these sources of energy can be effectively used to power remote sensors, the structural and biological communities have placed an emphasis on scavenging vibrational energy with piezoelectric materials. This article will review recent literature in the field of power harvesting and present the current state of power harvesting in its drive to create completely self-powered devices.

• Open/close A review on structural enhancement and repair using piezoelectric materials and shape memory alloys

  Quan Wang and Nan Wu 2012 Smart Mater. Struct. 21 013001 Tag this article

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  In the past two decades, the active and controllable mechanical properties of piezoelectric materials and shape memory alloys have been widely employed in structural enhancement and repair with remarkable and interesting research findings. This article is designed to introduce and review these research findings. The active electromechanical property of piezoelectric materials is presented first. The research findings on both structural stability enhancement of engineering structures and repair of cracked/notched and delaminated structures under static and dynamic loadings via the piezoelectric materials follow. The active thermo-mechanical property of shape memory alloys and their applications in structural enhancement and repair are also briefly presented. Limitations of the current studies and recommended future endeavors are summarized as well. This review sums up different methodologies and designs in structural enhancement and repair using piezoelectric materials and shape memory alloys to promote new applications in the area.

• Open/close Polymer optical fiber sensors—a review

  Kara Peters 2011 Smart Mater. Struct. 20 013002 Tag this article

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  Polymer optical fibers (POFs) have significant advantages for many sensing applications, including high elastic strain limits, high fracture toughness, high flexibility in bending, high sensitivity to strain and potential negative thermo-optic coefficients. The recent emergence of single-mode POFs has enabled high precision, large deformation optical fiber sensors. This article describes recent advances in both multi-mode and single-mode POF based strain and temperature sensors. The mechanical and optical properties of POFs relevant to strain and temperature applications are first summarized. POFs considered include multi-mode POFs, solid core single-mode POFs and microstructured single-mode POFs. Practical methods for applying POF sensors, including connecting and embedding sensors in structural materials, are also described. Recent demonstrations of multi-mode POF sensors in structural applications based on new interrogation methods, including backscattering and time-of-flight measurements, are outlined. The phase–displacement relation of a single-mode POF undergoing large deformation is presented to build a fundamental understanding of the response of single-mode POF sensors. Finally, this article highlights recent single-mode POF based sensors based on polymer fiber Bragg gratings and microstructured POFs.