Natural frequency analysis of laminated piezoelectric beams with arbitrary polarization directions

Piezoelectric devices exhibit unique properties that vary with different vibration modes,closely influenced by their polarization direction.This paper presents an analysis on the free vibration of laminated piezoelectric beams with varying polarization directions,using a state-space-based differential quadrature method.First,based on the electro-elasticity theory,the state-space method is extended to anisotropic piezoelectric materials,establishing state-space equations for arbitrary polarized piezoelectric beams.A semi-analytical solution for the natural frequency is then obtained via the differential quadrature method.The study commences by examining the impact of a uniform polarization direction,and then proceeds to analyze six polarization schemes relevant to the current research and applications.Additionally,the effects of geometric dimensions and gradient index on the natural frequencies are explored.The numerical results demonstrate that varying the polarization direction can significantly influence the natural frequencies,offering distinct advantages for piezoelectric elements with different polarizations.This research provides both theoretical insights and numerical methods for the structural design of piezoelectric devices.

SINGULAR BEHAVIORS OF INTERFACIAL CRACKS IN 2D MAGNETOELECTROELASTIC BIMATERIALS

The singular characteristics of stress, electric displacement and magnetic induction fields near the tip of impermeable interracial cracks in two-dimensional magnetoelectroelastic bimaterials are studied using the generalized Stroh formalism. Two types of singularities are obtained： one is the oscillating singularity 1/2±iε, the other is the non-oscillating singularity 1/2±κ. It is found that the non-zero parameters ε and κ cannot coexist for one transversely isotropic MEE bimaterial, a similar result is obtained for transversely isotropic piezoelectric bimaterials.

Application of the homotopy analysis method to nonlinear characteristics of a piezoelectric semiconductor fiber

Based on the nonlinear constitutive equation,a piezoelectric semiconductor(PSC)fiber under axial loads and Ohmic contact boundary conditions is investigated.The analytical solutions of electromechanical fields are derived by the homotopy analysis method(HAM),indicating that the HAM is efficient for the nonlinear analysis of PSC fibers,along with a rapid rate of convergence.Furthermore,the nonlinear characteristics of electromechanical fields are discussed through numerical results.It is shown that the asymmetrical distribution of electromechanical fields is obvious under a symmetrical load,and the piezoelectric effect is weakened by an applied electric field.With the increase in the initial carrier concentration,the electric potential decreases,and owing to the screen-ing effect of electrons,the distribution of electromechanical fields tends to be symmetrical.

Interfacial fracture analysis for a two-dimensional decagonal quasi-crystal coating layer structure

The interface crack problems in the two-dimensional(2D)decagonal quasicrystal(QC)coating are theoretically and numerically investigated with a displacement discontinuity method.The 2D general solution is obtained based on the potential theory.An analogy method is proposed based on the relationship between the general solutions for 2D decagonal and one-dimensional(1D)hexagonal QCs.According to the analogy method,the fundamental solutions of concentrated point phonon displacement discontinuities are obtained on the interface.By using the superposition principle,the hypersingular boundary integral-differential equations in terms of displacement discontinuities are determined for a line interface crack.Further,Green’s functions are found for uniform displacement discontinuities on a line element.The oscillatory singularity near a crack tip is eliminated by adopting the Gaussian distribution to approximate the delta function.The stress intensity factors(SIFs)with ordinary singularity and the energy release rate(ERR)are derived.Finally,a boundary element method is put forward to investigate the effects of different factors on the fracture.

On-chain is not enough:Ensuring pre-data on the chain credibility for blockchain-based source-tracing systems

The blockchain provides a reliable and scalable method for enabling source-tracing functionality in large-scale Internet of Things(IoT)systems.Traditional blockchain-based source tracing applications are generally based on the hypothesis that the raw data collected by each IoT node are credible and consistent,which however may not always be the truth.As no mechanism ensures the reliability of the original data collected from the IoT devices,these data may be accidently screwed up or maliciously tampered with before they are uploaded on-chain.To address this issue,we propose the Multi-dimensional Certificates of Origin(MCO)method to filter out the potentially incredible data-till all the data uploaded to the chain are credible.To achieve this,we devise the Multidimensional Information Cross-Verification(MICV)and Multi-source Data Matching Calculation(MDMC)methods.MICV verifies whether a to-be-uploaded datum is consistent or credible,and MDMC determines which data should be discarded and which data should be kept to retain the most likely credible/untampered ones in the circumstance when data inconsistency appears.Large-scale experiments show that our scheme ensures on the credibility of data and off the chain with an affordable overhead.

Three-dimensional interfacial fracture analysis of a one-dimensional hexagonal quasicrystal coating

In this paper, the three-dimensional(3D) interfacial fracture is analyzed in a one-dimensional(1D) hexagonal quasicrystal(QC) coating structure under mechanical loading. A planar interface crack with arbitrary shape is studied by a displacement discontinuity method. Fundamental solutions of interfacial concentrated displacement discontinuities are obtained by the Hankel transform technique, and the corresponding boundary integral-differential equations are constructed with the superposition principle.Green’s functions of constant interfacial displacement discontinuities within a rectangular element are derived, and a boundary element method is proposed for numerical simulation.The singularity of stresses near the crack front is investigated, and the stress intensity factors(SIFs) as well as energy release rates(ERRs) are determined. Finally, relevant influencing factors on the fracture behavior are discussed.

Thermal-induced interfacial behavior of a thin one-dimensional hexagonal quasicrystal film

In this paper,we investigate the interfacial behavior of a thin one-dimensional(1D)hexagonal quasicrystal(QC)film bonded on an elastic substrate subjected to a mismatch strain due to thermal variation.The contact interface is assumed to be nonslipping,with both perfectly bonded and debonded boundary conditions.The Fourier transform technique is adopted to establish the integral equations in terms of interfacial shear stress,which are solved as a linear algebraic system by approximating the unknown phonon interfacial shear stress via the series expansion of the Chebyshev polynomials.The expressions are explicitly obtained for the phonon interfacial shear stress,internal normal stress,and stress intensity factors(SIFs).Finally,based on numerical calculations,we briefly discuss the effects of the material mismatch,the geometry of the QC film,and the debonded length and location on stresses and SIFs.

Meteorological Influence on Tissue Expander-Related Major Infection

Background Infection is a relevant complication of tissue expander surgery that may compromise the flap.The effects of meteorological variables on surgical site infection have been observed in many surgeries;however,their influence on tissue expander infection is unknown.Methods We identified tissue expander implantation and infection based on their International Classification of Diseases,10th revision,codes in electronic hospitalization summary reports of 26 cities from January 1,2014 to December 31,2015.The data of the present study were collected for administrative purposes without any personal identifiers.The Cox proportional hazard model was used to investigate the association between meteorological variables and tissue expander-related major infection with six covariates.Results A total of 3,089 patients were enrolled.Of them,8.7%experienced a major infection during the study period.The optimal daily average temperature was between 22.9℃and 26.8℃,and the risk of major infection was significantly decreased in this range.The minimal infection temperature was 24.4℃,with a hazard ratio of 0.85.When the average relative humidity was 37%,the infection risk was minimal with a hazard ratio of 0.86;however,a relative humidity of≥79%significantly increased the risk of infection.Conclusions This is the first study to investigate the impact of temperature and relative humidity on tissue expander-related major infection.Our study suggests that there may be an optimal range of both temperature(22.9℃–26.8℃)and relative humidity(<79%)that can lower the risk of major infection after tissue expander implantation.

Determination of the Fracture Toughness of Glasses via Scratch Tests with a Vickers Indenter

Fracture toughness is an important index in safety evaluation for materials and structures.Its convenient and accurate characterization has attracted extensive attention.For small specimens,traditional testing methods of fracture toughness are not suitable due to limitations in sample size and shape.In this work,a new formula is proposed to determine the fracture toughness of glasses using scratch tests with a Vickers indenter based on dimensional analysis and finite element analysis.Fracture toughness of glasses could be calculated with elastic modulus,crack depth of scratched materials and normal force applied during the scratch tests.The effects of plastic deformation and interfacial friction between the Vickers indenter and scratched materials are considered,and the crack shape is consistent with experimental observations.The proposed formula is verified by comparing the fracture toughness of soda-lime and borosilicate glasses obtained from scratch tests with those obtained via indentation tests.This work provides an alternative method to determine the fracture toughness of glass materials.

Dielectric Breakdown Model for an Electrically Semi-Permeable Penny-Shaped Crack in Three-Dimensional Piezoelectric Media

The dielectric breakdown（DB） model for a penny-shaped crack under a semipermeable boundary condition in a three-dimensional piezoelectric medium is studied.An approximate analytical solution is derived by using the boundary integral equation with extended displacement discontinuity,and the corresponding boundary element method with double iterative approaches is developed to analyze the semi-permeable crack.The effect of electric boundary conditions on crack faces is discussed on the basis of DB model.By comparing the DB model with the polarization saturation（PS） model for different piezoelectric materials,some interesting phenomena related to the electric yielding zone and local J-integral are observed.