Applications of smart piezoelectric materials in a wireless admittance monitoring system (WiAMS) to Structures—Tests in RC elements

Case Studies in Construction Materials, Volume 5, December 2016, Pages 1-18

Constantin E. Chalioris, Chris G. Karayannis, Georgia M. Angeli, Nikos A. Papadopoulos, Maria J. Favvata, Costas P. Providakis

Abstract:The application of an innovative real-time structural health monitoring system is studied through tests performed on flexural and shear-critical reinforced concrete elements subjected to monotonic and cyclic loading. The test set-up involves a Wireless impedance/Admittance Monitoring System (WiAMS) that comprises specially manufactured small-sized portable devices to collect the voltage frequency responses of an array of smart piezoelectric transducers mounted on structural members of reinforced concrete constructions. Damage detection and evaluation is achieved using the in-situ measurements of the integrated piezoelectric sensors/actuators signals at the healthy state of the member and at various levels of damage during testing. Three different installations of Piezoelectric lead Zirconate Titanate (PZT) transducers are examined: (a) epoxy bonded PZTs on the surface of the steel reinforcing bars of the flexural elements, (b) PZTs embedded inside the concrete mass of the shear-critical beams and (c) externally epoxy bonded PZTs attached to the concrete surface of the tested elements. The smart piezoelectric materials have been pre-installed before testing based on the potential flexural and shear cracking of the elements. Quantitative assessment of the examined damage levels using values for the statistical damage index is also presented and discussed. Voltage signals and index values acquired from the PZTs’ measurements using the proposed wireless monitoring technique demonstrated obvious discrepancies between the frequency response of the healthy and the examined damage levels for every tested element. These differences clearly indicate the presence of damage, whereas their gradation reveals the magnitude of the occurred damage. Promising results concerning the prediction of the forthcoming fatal failures at early damage stages have also been derived.

Electrospun uniaxially-aligned composite nanofibers as highly-efficient piezoelectric material

Ceramics International, Volume 42, Issue 2, Part A, 1 February 2016, Pages 2734-2740

Caroline Lee, David Wood, Dennis Edmondson, Dingyu Yao, Ariane E. Erickson, Ching Ting Tsao, Richard A. Revia, Hyungsub Kim, Miqin Zhang

Abstract:A uniaxially-aligned nanofibrous matrix was produced by electrospinning and it demonstrates strong piezoelectric property. The matrix is composed of highly-aligned polyvinylidene fluoride (PVDF) polymer nanofibers embedded with barium titanate (BaTiO3) nanoparticles. Measurements of piezoelectrically generated voltages in response to mechanical deformation of BaTiO3–PVDF composite nanofibers with various concentrations of BaTiO3 nanoparticles showed that the magnitude of the resultant voltage increases as the nanoparticle concentration increases. PVDF nanofibers with 16 wt% BaTiO3 nanoparticles exhibit piezoelectric output voltages that are 1.7 times greater than PVDF fibers without BaTiO3 nanoparticles when subjected to the same degree of deformation. Scanning electron microscopy confirmed the uniaxial alignment of PVDF nanofibers with individual fiber diameters of ~200 nm as well as the presence of BaTiO3 deposits. The increased piezoelectric response of uniaxially-aligned BaTiO3–PVDF nanofibers in comparison with randomly oriented PVDF fibers and thin films suggests possible uses for such nanofibers in energy harvesting and as power sources in miniaturized electronic devices like wearable smart textiles and implantable biosensors.

Different interface models for calculating the effective properties in piezoelectric composite materials with imperfect fiber–matrix adhesion

Composite Structures, In Press, Corrected Proof, Available online 11 February 2016

Humberto Brito-Santana, Ricardo de Medeiros, Reinaldo Rodriguez-Ramos, Volnei Tita

Abstract:Piezoelectric materials are able to produce an electrical response when mechanically stressed (sensors) and inversely high precision motion can be obtained with the application of an electrical field (actuators). The macroscopic properties of piezoelectric composites depend upon the properties and the interfacial bonding conditions of the constituent phases, and the microstructures of the composites. In the present work, a new imperfect interface model for a thin elastic interface is derived. Square unit cell model was used to calculate all coefficients of the material tensor. The calculation was performed via FE package ABAQUS™. A computational procedure, based on Python language, was developed to systematically calculate all RVE effective coefficients. Comparisons to classical Hashin’s and Nairn’s interface model show very accurate agreement for debonding and perfect boding interface.

Size-dependent buckling and postbuckling behavior of piezoelectric cylindrical nanoshells subjected to compression and electrical load

Materials & Design, In Press, Accepted Manuscript, Available online 20 May 2016

S. Sahmani, M.M. Aghdam, A.H. Akbarzadeh

Abstract:This paper studies the nonlinear buckling and postbuckling characteristics of piezoelectric cylindrical nanoshells subjected to an axial compressive mechanical load and an electrical load in the presence of surface free energy effects. The electrical field is applied along the transverse direction. A size-dependent shell model is adopted based on the Gurtin-Murdoch elasticity theory and von Karman geometrical nonlinearity. To satisfy the balance conditions on the surfaces of the nanoshell, a linear variation is considered for the normal stress of the bulk through the thickness. A boundary layer theory is employed including surface energy effects in conjunction with the effects of nonlinear prebuckling deformation, large deflections in the postbuckling regime and initial geometrical imperfections. Afterwards, a two-stepped singular perturbation technique is employed to obtain the size-dependent critical buckling load and the associated postbuckling equilibrium path for alternative electric loadings. It is found that the surface free energy and electrical load can cause an increase or decrease on the critical buckling load and the associated postbuckling strength of a nanoshell depending on the sign of surface properties and applied voltage. These anticipations are the same for the both perfect and imperfect piezoelectric nanoshells.

Crack analyses in porous piezoelectric brittle materials by the SBFEM

Engineering Fracture Mechanics, Volume 160, July 2016, Pages 78-94

Jan Sladek, Vladimir Sladek, Slavomir Krahulec, Chongmin Song

Abstract:The scaled boundary-finite element method (SBFEM) is employed to analyze cracks in porous piezoelectric solids. A large (magistral) crack and a short crack emanating from a single pore are analyzed. These cracks with their tips in the solid skeleton have the weakening effects on the fracture strength. The crack tip region is considered as a subdomain where both the crack tip and pores are modeled inside the piezoelectric skeleton. The remaining part of the analyzed domain is modeled with effective material properties obtained from the analysis on the representative volume element (RVE). A regular distribution of circular voids is considered in the numerical analyses. The scaled boundary-finite element method (SBFEM) is applied to solve all the boundary value problems.