This paper demonstrates the feasibility of forming multi-functional graphene based surfaces capable of thermal heating for de-icing applications. Developmental ink layers are deposited onto composite laminate skin surfaces and used to melt the ice-skin interface by Joule heating while simultaneously developing a thermal strain in the skin structure to develop a shear stress to debond the ice-skin interface. The electrical properties, microstructure, processing parameters, heat transfer and electro-thermal response of the electrically conductive developmental ink layers are examined along with the change in shape of the composite structure with temperature. Initial de-icing tests are demonstrated. Application sectors for the multifunctional skins include exposed instrumentation housings, structural members exposed to extreme environments, such as wind turbines, and transport (aerospace). The opportunity to limit the extent of ice build-up on structures has broad application opportunities to provide light -weight structures with reduced material costs and fuel saving for mobile applications and improved performance for instrumentation.
KEYWORDS: Composites, Bistability, Energy harvesting, Magnetism, Systems modeling, Microsoft Foundation Class Library, Resistors, Motion models, Manufacturing, Carbon
In this paper a bistable composite cantilever beam comprising asymmetric laminates is studied for vibration energy harvesting applications. An additional magnetic bistability is introduced to the harvesting system to lower the level of excitation that triggers the snap-through for the cantilever from one stable state to another, while retaining the favorable broadband performance. In order to achieve the, the cantilever beam is fitted with a permanent magnet at its tip that is oriented so that there is magnetic repulsion with a stationary magnet. The system performance can be adjusted by varying the separation between the magnets. Experimental results reveal that the use of magnetic bistability enhances broadband performance and improves the output power within a certain level of drive level and magnet separation. The load-deflection characteristic of the bistable beam is experimentally determined, and is subsequently used to model the system by a reduced single-degree-of-freedom (SDOF) system having the form of the Duffing equation for a double-well potential system. The dynamics of the beam are investigated using bifurcation diagrams and shows that the qualitative behavior given by the experimentally measured response is predicted well by the simple SDOF model.
KEYWORDS: Bismuth, Microsoft Foundation Class Library, Modeling, Energy harvesting, Digital image correlation, Resistance, Bistability, Manufacturing, Shape analysis, Cameras
The need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted interest in recent years for energy harvesting technologies capable of capturing energy from broadband ambient vibrations. Encouraging results have been reported for an arrangement of piezoelectric layers attached to carbon fiber / epoxy laminates which possess bistability by virtue of their specific asymmetric stacking sequence. The inherent bistability of the underlying structure is exploited for energy harvesting since a transition from one stable configuration to another, or ‘snap-through’, is used to repeatedly strain the surface-bonded piezoelectric and generate electrical energy. Existing studies, both experimental and modelling, have been limited to simple geometric laminate shapes, restricting the scope for improved energy harvesting performance by limiting the number of design variables. In this paper we present an analytical model to predict the static shapes of laminates of any desired profile, validated experimentally using a digital image correlation system. Good accuracy in terms of out-of-plane displacements (5-7%) are shown in line with existing square modelling results. The static model is then mapped to a dynamics model and used to compare results against an experimental study of the harvesting performance of an example arbitrary geometry piezoelectric-laminate energy harvester.
In this paper effect of the orientation of the main crystallographic axes on the piezoelectric anisotropy and hydrostatic
parameters of 2–2 parallel-connected single crystal (SC) / auxetic polymer composites is analysed. SCs are chosen
among the perovskite-type relaxor-ferroelectric solid solutions of (1 – x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 and xPb(In1/2Nb1/2)O3–yPb(Mg1/3Nb2/3)O3–(1 – x – y)PbTiO3. The SC layers in a composite sample are poled along the perovskite unit-cell [011] direction and characterised by mm2 symmetry. The orientation of the main crystallographic axes in the SC layer is observed to strongly influence the effective piezoelectric coefficients d*3j, g*3j, squared figured of merit d*3jg*3j, electromechanical coupling factors k*3j (j = 1, 2 and 3), and hydrostatic analogs of these parameters of the 2–2 composite. A comparison of values of d*3jg*3j was first carried out at d*31 ≠ d*32 in a wide range of orientations and volume-fraction. Large values of the effective parameters and inequalities | d*33 / d*3f | > 5 and | k*33 / k*3f | > 5 (f = 1 and 2) are achieved at specific orientations of the main crystallographic axes due to the anisotropy of elastic and piezoelectric properties of the SC component. The use of an auxetic polyethylene with a negative Poisson’s ratio leads to a significant increase in the hydrostatic parameters of the 2–2 composite. Particular advantages of the studied composites over the conventional ceramic / polymer composites are taken into account for transducer, hydroacoustic and energyharvesting applications.
KEYWORDS: Energy harvesting, Digital image correlation, Composites, Sensor networks, Electromagnetism, Microsoft Foundation Class Library, Bistability, Piezoelectric effects, Aerospace engineering, Electronic components
The need to power small electronic components, such as wireless sensor networks, has prompted interest in energy harvesting technologies capable of generating electrical energy from ambient vibrations. There has been a particular focus on piezoelectric materials and devices due to the simplicity of the mechanical to electrical energy conversion and their high strain energy densities compared to electrostatic and electromagnetic equivalents. This paper describes research on an arrangement of piezoelectric elements attached to a bistable asymmetric laminate to understand the dynamic response of the structure and power generation characteristics. The inherent bistability of the underlying structure is exploited for energy harvesting since 'snap-through' from one stable configuration to another is used to strain the piezoelectric materials bonded to the laminate and generate piezoelectric energy. Using high speed digital image correlation, a variety of dynamic modes of oscillation are identified in the bistable harvester. The sensitivity of such vibrational modes to changes in frequency and amplitude are investigated. Electrical power outputs are measured for repeatable snap-through events and are correlated with the modes of oscillation. The typical power generated is approximately 25mW and compares well with the needs of typical wireless senor node applications.
This paper presents a unique arrangement of bistable composite plates with piezoelectric patches bonded to its surface to
perform broadband vibration-based energy harvesting from ambient mechanical vibrations. These bistable nonlinear
devices have been shown to have improved power generation compared to conventional resonant systems and can be
designed to occupy smaller volumes than bistable magnetic cantilever systems. This paper presents the results of an
optimization study of bistable composites that are capable of generating greater electrical power from a smaller space by
discovering the correct geometric configuration for energy harvesting. Optimum solutions are investigated in a series of
design parameter studies intended to reveal the complex interactions of the physical constraints and design requirements.
The proposed approach considers the optimal choice of device aspect ratio, thickness, laminate stacking sequence, and
piezoelectric surface area. Increased electrical output is found for geometries and piezoelectric configurations which
have not been considered previously.
Simple and contactless methods for determining the health of metallic and composite structures are necessary
to allow non-invasive Non-Destructive Evaluation (NDE) of damaged structures. Many recognized damage
detection techniques, such as frequency shift, generalized fractal dimension and wavelet transform, have been
described with the aim to identify, locate damage and determine the severity of damage. These techniques are
often tailored for factors such as (i) type of material, (ii) damage patterns (crack, impact damage, delamination),
and (iii) nature of input signals (space and time). In this paper, a wavelet-based damage detection framework
that locates damage on cantilevered composite beams via NDE using computer vision technologies is presented.
Two types of damage have been investigated in this research: (i) defects induced by removing material to reduce
stiffness in a metallic beam and (ii) manufactured delaminations in a composite laminate. The novelty in the
proposed approach is the use of bespoke computer vision algorithms for the contactless acquisition of modal
shapes, a task that is commonly regarded as a barrier to practical damage detection. Using the proposed
method, it is demonstrated that modal shapes of cantilever beams can be readily reconstructed by extracting
markers using Hough Transform from images captured using conventional slow motion cameras. This avoids
the need to use expensive equipment such as laser doppler vibrometers. The extracted modal shapes are then
used as input for a wavelet transform damage detection, exploiting both discrete and continuous variants. The
experimental results are verified using finite element models (FEM).
This paper analyses strain and polarisation responses of 1-3 composites, which are related to the fibre and matrix properties. The validity of equations that predict the strain and polarisation of fibres from composite responses, and associated errors at high electric driving fields, are discussed. Surface profile measurements of single PZT rods in a polymer matrix, subjected to a static voltage, were made to investigate the effect of fibre aspect (diameter to length) ratio. Surface profiles, which show the active PZT rod extending from the passive polymer matrix, agree well with predictions made using finite element analysis. The results show that for a 1-3 composite to be treated as a homogeneous medium the fibre aspect ratio needs to be low. Commercially available PZT-5A composition fibres fabricated using four production methods were incorporated into 1-3 composites with fibre volume fractions ranging from 0.02 to 0.72, and with various aspect ratios, were evaluated. Strain-field and polarisation-field curves for the composites were obtained by testing the composites under electrical field cycles of ±2 kVmm-1. From these curves the strain and polarisation response of the fibres have been extracted using appropriate analytical equations. The saturation strain, saturation polarisation and coercive field values are reported for the four fibre types. The Viscous Plastic Process (VPP) and Viscous Suspension Spun (VSSP) fibres develop strains of approximately 4000 ppm. Reduced piezoelectric activity is seen in extruded fibres, which develop strains of 3000 ppm.
Commercially available PZT-5A composition fibres fabricated using four production methods were incorporated into 1-3 composites with fibre volume fractions ranging from 0.02 to 0.72. Measurements of the piezoelectric induced strain constants (d33 and d31), relative dielectric constants (e33), longitudinal coupling factors (k33) and stiffness' (s33) of the varying volume fraction composites are compared to analytical expressions in order to extract the fibre properties. Results show 1-3 composite data accurately follows the analytical trends. The Viscous Plastic Process (VPP) fibres are found to exhibit optimum material properties, which approach bulk material values. Reduced piezoelectric activity in extruded fibres is thought to be associated with a small grain size and high porosity. A second study, an optimisation of interdigitated electrode design, was performed using the finite element software ANSYS. The effect of the IDE geometry (electrode width and spacing) and PZT substrate thickness on the strain output of bulk PZT substrates was modelled. Results show optimal actuation occurs at electrode widths equal to half the substrate thickness, and for thin substrates the electrode finger spacing can be reduced to enable lower driving voltages.
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