Fabrication and experimental characterization of d31 telescopic piezoelectric actuators

A popular and useful piezoelectric actuator is the stack. Unfortunately with this type of actuation architecture the long lengths normally required to obtain necessary displacements can pose packaging and buckling problems. To overcome these limitations, a new architecture for piezoelectric actuators has been developed called telescopic. The basic design consists of concentric shells interconnected by end-caps which alternate in placement between the two axial ends of the shells. This leads to a linear displacement amplification at the cost of force; yet the force remains at the same magnitude as a stack and significantly higher than bender type architectures. This paper describes the fabrication and experimental characterization of three different telescopic prototypes. The actuator prototypes discussed in this paper mark a definitive step forward in fabrication techniques for complex piezoceramic structures. Materials Systems, Inc. has adapted injection molding for the fabrication of net shape piezoceramic actuators. Injection molding provides several advantages over conventional fabrication techniques, including: high production rate, uniform part dimensions, uniform piezoelectric properties, and reduced fabrication and assembly costs. Acrylate polymerization, developed at the University of Michigan, is similar to gelcasting, but uses a nonaqueous slurry which facilitates the production of large, tall, complex components such as the telescopic actuator, and is ideal for the rapid manufacture of unique or small batch structures. To demonstrate these fabrication processes a five tube telescopic actuator was injection molded along with a very tall three tube actuator that was cast using the acrylate polymerization method. As a benchmark, a third actuator was built from off-the-shelf tubes that were joined with aluminum end-caps. Each prototype's free deflection behavior was experimentally characterized and the results of the testing are presented within this paper.     

Coupled extensional vibrations of longitudinally polarized piezoceramic strips

A system of one-dimensional equations for coupled length-extensional, width-stretch, and symmetric width-shear vibrations of piezoceramic strips polarized in the length direction is derived from the two-dimensional, second-order plate equations by averaging the mechanical displacement and the electrostatic potential over the strip thickness. The boundary conditions correspond to the case of electrically forced vibrations. Theoretical values are compared with results of a previous analytical model and with experimental data.     

Formation of a sub-wavelength longitudinally polarized beam using a radially polarized controllable dark-hollow beam

On the basis of vector diffraction theory, the tightly focusing properties of radially polarized controllable dark-hollow (CDH) beams are examined theoretically. Calculation results demonstrate that by choosing the initial parameters of the proposed light beams suitably, a sub-wavelength (0.422λ) longitudinally polarized light beam with high beam quality (82.2%) can be formed without any filters. Meanwhile, we find that a relatively long depth of focus benefits from larger beam order. The dependence of the focal spot size on the parameters such as truncation parameter, variation constant, and beam order is also explored in detail. Moreover, an alternative method to generate the CDH beams is proposed.     

Numerical study of shear banding evolution in bulk metallic glass composites

In this article, a systematic simulation was performed to demonstrate the detailed shear banding evolution in bulk metallic glass (BMG) composites subjected to the tension, and the relation between microstructures and tensile ductility was therefore elucidated. Free volume was adopted as an internal state variable to characterize the shear banding nucleation, growth and coalescence in BMG matrix with the help of free volume theory, which was incorporated into ABAQUS finite element method (FEM) code as a user material subroutine. The present numerical method was firstly verified by comparing with the corresponding experimental results, and then parameter analyses were conducted to discuss the impacts of particle volume fraction, particle shape, particle orientation and particle yielding strength on the enhancement efficiency of the tensile ductility of BMG composites.     

Micromechanics of piezoelectric composites with improved effective piezoelectric constant

This paper is concerned with the derivation of a micromechanics model of a new type of piezoelectric fiber reinforced composite (PFRC) materials. A continuum mechanics approach is employed to determine the effective properties of these composites. The piezoelectric fibers of these composites are considered to be electroded at the fiber–matrix interface such that the electric fields in the fiber and matrix become equal in the direction transverse to the fiber direction. The model has been verified with the existing models. The present model also predicts that the effective piezoelectric coefficient of these PFRC which accounts for the actuating capability in the fiber direction due to the applied field in the direction transverse to the fiber direction improves over the corresponding coefficient of the material of the piezoelectric fibers if the fiber volume fraction exceeds a critical fiber volume fraction.     

Numerical and experimental investigation on lap shear fracture of Al/CFRP laminates

This paper presents a new approach to numerically investigate the lap shear fracture of a hybrid laminate made of Carbon Fibre Reinforced Plastic (CFRP) and metal foil plies (e.g. aluminium), validated by corresponding experiments. The numerical Finite Element (FE) model of the hybrid laminate, subjected to lap shear fracture, is composed of five laminas with alternating metal/CFRP layers with cohesive elements lying within Al/CFRP interface. In the FE model, individual CFRP laminas are assumed as an orthotropic homogenized continuum under plane stress, and aluminium facesheets are modelled as an elastic–plastic continuum. The Al/CFRP interface is represented via quadratic cohesive elements, the constitutive law of which is an exponentially decaying law representing the degrading behaviour of the interface (implemented as user element in ABAQUS). The numerical model captures the experimentally obtained results with minimal error, and predicts the failure modes successfully. The influence of specimen geometry (e.g. overlap length, total length, and total width) on lap shear fracture response is analyzed in detail in this study, too, in order to confirm the specimen design for the test, as there is still no corresponding test standard for hybrid laminates.     

Multi-Inclusion modeling of multiphase piezoelectric composites

Recent work on multifunctional materials has shown that a functionally graded interface between the fiber and matrix of a composite material can lead to improved strength and stiffness while simultaneously affording piezoelectric properties to the composite. However the modeling of this functional gradient is difficult through micromechanics models without discretizing the gradient into numerous layers of varying properties. In order to facilitate the design of these multiphase piezoelectric composites, accurate models are required. In this work, Multi-Inclusion models are extended to predict the effective electroelastic properties of multiphase piezoelectric composites. To evaluate the micromechanics modeling results, a three dimensional finite element model of a four-phase piezoelectric composite was created in the commercial finite element software ABAQUS with different volume fractions and aspect ratios. The simulations showed excellent agreement for multiphase piezoelectric composites, and thus the modeling approach has been applied to study the overall electroelastic properties of a composite with zinc oxide nanowires grown on carbon fibers embedded in the polymer. The results of this case study demonstrate the importance of the approach and show the system cannot be accurately modeled with a homogenized interphase.     

Nonlinear shear properties of spruce softwood: Numerical analyses of experimental results

Determination of material parameters from experimental tests often rely on simplifying assumptions like the existence of uniform stress and strain fields within the considered part of the test specimen. However, more detailed analyses usually show that the stress and strain fields differ from the assumed (nominal) uniform distributions. In order to utilize the potential of numerical analyses of wooden structures by the FEM method, the nominal material parameters measured directly from tests need to be re-evaluated in order to make them more useful for FEM models and to make FEM models more reliable.Experimental data from shear testing of clear wood from Norway spruce was analysed numerically with a bilinear material law in shear. The inherent material parameters were fitted to the experimental behaviour by means of optimization methods in conjunction with FEM analyses. The study included six Arcan test configurations comprising the three orthotropic material planes of wood, and covered the whole loading range until failure. Compared to numerical results, it was found that stiffness values measured were too high, and that downward adjustments in the range of 5–30% were required. Linear limit stresses between 40% and 60% of the nominal shear strengths were found, whilst the tangent moduli ranged between 30% and 70% of the linear elastic shear moduli. The rolling shear plane RT showed most nonlinearity and the LT plane least. Analyses with modified bilinear parameters showed good correspondence with experimental findings. The parameters were found to be relatively well adapted by Weibull distributions.     

Effect of aged binder on piezoelectric properties of cement-based piezoelectric composites

Age-dependent piezoelectric properties of cement piezoelectric composites containing cement-based binder and 50 vol. % PZT piezoelectric inclusions are conducted. The effect of binder with 10 to 50 % cement replaced by slag and fly ash is investigated. Specimens are polarized by 1.5 kV/mm for 30 min when the curing time reaches 7, 28 and 56 days, respectively. Experimental values are measured daily till 120 days after the polarization. Prior to polarization, dielectric loss needs to be less than 0.73 to guarantee the feasibility of polarization. Piezoelectric properties including d ₃₃, g ₃₃ and ?_r are age-dependent unless the age is higher than 60 days after the polarization. The electromechanical coupling coefficient κ_t is independent of the ages. The curing time shows less efficient to piezoelectric properties while hydration reaction is completed. 20 vol. % cement replaced by slag or fly ash provides optimum d ₃₃ and g _33. Compared with slag replacement, fly ash replacement can diminish ?_r, but increase κ_t. In addition, a modified equation to calculate the dielectric constant of PZT/cement composites is also proposed.     

Numerical and experimental failure analysis of screwed single shear joints in wood plastic composite

In this research, effects of end distances and thicknesses of side and main members on failure loads and also modes of failure of single shear plane joint, made on wood plastic composite (WPC) were studied, both experimentally and numerically as well. Yamada-Sun failure criterion was used to determine failure loads of this kind of joints fabricated on WPC and results were compared with that of experimental observations. Numerical analysis was made by making use of ABAQUS finite element (FE) software. Experiments were conducted according to ASTM D-1037. Predicted failure loads by numerical models were in good agreement with those observed experimentally. Results have indicated that failure load of tested joint is dependent on end distance and thickness of corresponding members as well. Failure modes were determined both by numerical models and tested joints. FE models were used to perform stress analysis.     

Damping of compression and shear piezoelectric accelerometers byelectromechanical feedback

It is shown that the very pronounced resonance peak in the frequency entirely by a simple modification of existing accelerometers, providing them with an electrical sensor output as well as an electrical actuator input, and using a charge amplifier in a feedback path between the sensor output and the actuator input. Because a piezoelectric accelerometer is normally read out by a charge amplifier, no extra circuitry (expense) is necessary to provide this electromechanical feedback. It is shown that a maximally flat response (Butterworth) can be obtained with little peaking (approximately 2 dB) and excellent dynamic stability, which makes the acceleration usable up to its resonance frequency     

Finite element characterization and parametric analysis of the nonlinear behaviour of an actual d 15 shear MFC

Nonlinear dependence between mechanical deformation and applied voltage has been experimentally observed on a recently manufactured lengthwise poled piezoelectric d ₁₅ shear macro-fibre composite (MFC) transducer. This work proposes a methodology to model this phenomenon by combining the nonlinear behaviour of the constituent piezoceramic fibre (electric field dependence of material properties) with a finite element homogenization technique to evaluate the resulting nonlinearity of the effective properties of the d ₁₅ MFC. Results show that the experimentally observed nonlinear behaviour of d ₁₅ MFC is reasonably well predicted by the proposed methodology indicating that this behaviour could be explained by an electric field dependence of the piezoceramic fibre material properties. Results also show that d ₁₅ and ${\epsilon_{11}^T}$ coefficients of the d ₁₅ MFC are not significantly reduced by the MFC packaging, while e ₁₅ and G ₁₃ coefficients are reduced by 90 %, compared to the piezoceramic fibre ones. A conducted parametric analysis indicates that the actuation performance of the d ₁₅ MFC transducer could be improved by increasing the active layer thickness.     

Effective anti-plane properties of piezoelectric fibrous composites

Anti-plane shear of piezoelectric fibrous composites is theoretically investigated. The geometry of composites is described by the 2-dimensional geometry in a section perpendicular to the unidirectional fibers. The previous constructive results obtained for scalar conductivity problems are extended to piezoelectric anti-plane problems. First, the piezoelectric problem is written in the form of the vector-matrix ${\mathbb{R}}$ -linear problem in a class of double periodic functions. In particular, application of the zeroth-order solution to the ${\mathbb{R}}$ -linear problem yields a vector-matrix extension of the famous Clausius–Mossotti approximation. The vector-matrix problem is decomposed into two scalar ${\mathbb{R}}$ -linear problems. This reduction allows us to directly apply all the known exact and approximate analytical results for scalar problems to establish high-order formulae for the effective piezoelectric constants. Special attention is paid to non-overlapping disks embedded in a two-dimensional background.     

Numerical and experimental analyses of singular electro-elastic fields around a V-shaped notch tip in piezoelectric materials

A super V-shaped notch tip element that simulates electro-elastic behavior near a V-shaped notch tip is first developed based on one-dimensional finite element eigensolutions. The present element is then incorporated with standard four-node hybrid electro-elastic field elements to calculate electro-elastic singularity orders, singular strain distributions and generalized stress intensity factors ahead of V-shaped notch tips in three-point-bending piezoelectric specimens with notch angles α = 0°, 30°, 60° and 90°, respectively. The present numerical solutions are compared with those obtained from the moiré interferometry experiment technique. Finally, the effect of the V-shaped notch angle and electric field on singular electro-elastic fields is also discussed.     

Dynamic analysis of sandwich cement-based piezoelectric composites

Theoretical analysis of a sandwich cement-based piezoelectric composite is presented based on the theory of piezo-elasticity. The steady-state responses of two kinds of this composite under different loading cases are obtained by the use of displacement method. The effects of piezoelectric phases on the performance of this kind of devices are simulated and discussed. The solutions are compared with both the numerical and experimental results, and good agreements are found. Sandwich cement-based piezoelectric composites have great application potential in civil structure health monitoring. The results obtained in this paper are beneficial to the design of this kind of smart devices.     

Numerical and experimental stiffness characterisations applied to soft textile composites for tensile structures

This paper presents numerical and experimental stiffness characterisation methods for soft composite textile membranes used in fabric roof structures. The studied material is a polyester plain-woven fabric coated with PVC. We present three numerical textile composite micro-structure models. They are integrated in stiffness calculation software programs which are used to identify linear elastic characteristics for a coated fabric sample. The first two models are based on the laminated thin plate theory; the fabric is represented by a stacking of unidirectionally-reinforced layers, or by the ‘Crimp Model’. The third one considers a geometrical approach to the basic cell of the fabric; the elastic characteristics are calculated by assembly of the meshing elements. In addition, an inverse and experimental stiffness identification method, based on biaxial tensile tests conducted (in orthotropic directions), is proposed. Load-controlled tests are conducted on cross-shaped samples with different loading ratios in warp and weft directions: 1/1,1/2,2/1.     

Numerical studies on the effective shear modulus of particle reinforced composites with an inhomogeneous inter-phase

Numerical studies on the effective shear modulus of particle reinforced composites with an inhomogeneous inter-phase are performed. The influences of many parameters to the equivalent shear modulus of composites are carefully analyzed, including the inter-phase thickness, variation of interfacial properties, boundary conditions and volume fraction of particles, etc. Numerical results show that the Poisson ratio can be assumed as a constant across the whole inter-phase zone in the computation. The form of property variation across the inter-phase also greatly affects the effective shear modulus of composite. Numerical results predicted by the rigid boundary conditions are remarkably higher than those by the free boundary conditions and the exact solutions. The reasonability and exactness of the available models for predicting the effective shear modulus of composites are accessed by the numerical results in the present work.     

Multicoated elliptic fibrous composites of piezoelectric and piezomagnetic phases

A theoretical framework is developed to investigate the magnetoelectroelastic potential in a multicoated elliptic fibrous composite with piezoelectric and piezomagnetic phases. We generalize the classic work of Rayleigh (1892) to obtain the electrostatic potential in ordered conductive composites and its extension to a disordered system ( [Kuo, 2010] and [Kuo and Chen, 2008]) to the current coupled magnetoelectroelastic multicoated elliptic composites. We combine the methods of complex potentials with a re-expansion formulae and the generalized Rayleigh’s formulation to obtain a complete solution of the multi-field many-inclusion problem. It is shown that the coefficients of field expansions can be written in the form of an infinite set of linear algebraic equations. Numerical results are presented for several configurations. We use this method to study BaTiO₃-CoFe₂O₄ composites and find that, with appropriate coating, the effective magnetoelectric voltage coefficient can be enhanced with one order of magnitude compared to their non-coating counterpart.     

PVDF/PZNZT压电复合材料的结构与性能

为了扩展压电复合材料的应用领域,首先,通过固相合成法制备了0-3型聚偏氟乙烯(PVDF)/Pb(Zn_1/3Nb_2/3)_0.05Zr_0.47Ti_0.48O₃ (PZNZT)压电复合材料;然后,研究了PVDF含量对PVDF/PZNZT复合材料物相、显微结构及性能的影响。结果表明:PZNZT陶瓷粉料与PVDF粉料混合后,其平均粒度接近于纯PVDF粉料的。于220℃下烧结后, PVDF/PZNZT复合材料在XRD谱图中主要显现出PZNZT钙钛矿结构的衍射峰。当PVDF含量较低时, PZNZT陶瓷晶粒间的结合较松散;随着PVDF含量的增加,陶瓷晶粒几乎都被PVDF相包围。因显微结构不同,不同PVDF含量的PVDF/PZNZT复合材料在极化电场中呈现出不同的串、并联电路。极化后, 5wt% PVDF/PZNZT复合材料的电性能最佳,其介电常数为116、介电损耗tan δ为0.04、压电常数为48 pC/N且机电耦合系数为0.28。随PVDF含量的增加, PVDF/PZNZT复合材料的居里温度降低,维氏硬度有所增加,但仍小于纯PZNZT压电陶瓷的硬度。所得结论显示PVDF/PZNZT压电复合材料的性能可以满足水声、电声及超声换能器等的要求。