Showing papers by "Yue-Sheng Wang published in 2009"

Effects of material parameters on elastic band gaps of two-dimensional solid phononic crystals

Abstract: In this paper we study the influences of the material parameters on phononic band gaps of two-dimensional solid phononic crystals. The analysis begins with the basic wave equations and derives the material parameters directly determining band gaps. These parameters include the mass density ratio, the shear modulus ratio, and Poisson’s ratios of the scatterer and host materials (or equivalently, the wave velocity ratio, the acoustic impedance ratio, and Poisson’s ratios). The effects of these parameters on phononic band gaps are discussed in details for phononic crystals with different filling fractions and lattice forms for both antiplane and in-plane wave modes. Band gaps are calculated by the plane wave expansion method. The results show that for the antiplane mode, the mass density ratio predominantly determines the band gap, while that for the in-plane mode, both mass density ratio and shear modulus ratio play equally important roles. The maximum band gap will appear at both large density ratio and sh...

Tuning of band gaps for a two-dimensional piezoelectric phononic crystal with a rectangular lattice

Abstract: In this paper, the elastic wave propagation in a two-dimensional piezoelectric phononic crystal is studied by considering the mechanic–electric coupling. The generalized eigenvalue equation is obtained by the relation of the mechanic and electric fields as well as the Bloch–Floquet theorem. The band structures of both the in-plane and anti-plane modes are calculated for a rectangular lattice by the plane-wave expansion method. The effects of the lattice constant ratio and the piezoelectricity with different filling fractions are analyzed. The results show that the largest gap width is not always obtained for a square lattice. In some situations, a rectangular lattice may generate larger gaps. The band gap characteristics are influenced obviously by the piezoelectricity with the larger lattice constant ratios and the filling fractions.

Analysis of wave propagation and localization in periodic/disordered layered composite structures by a mass-spring model

Abstract: The band structure and the displacement field of elastic waves in periodic/disordered layered composite structures of finite width are investigated by a simple mass-spring model. In the case of comparable stiffness, the density contrast plays a dominant role for the center layer disorder to obtain localized wave modes within the band gap. On the other hand, in the case of comparable density contrast, the number and the position of the localized modes can be adjusted by changing the stiffness of the center layer. Compared to the soft and nearly cracked disorders situated between two layers with a lower density, the band structure and the displacement are quite different from the case between two layers with a higher density.

Band gap behaviours of periodic magnetoelectroelastic composite structures with Kagome lattices

Abstract: In this paper, the elastic wave propagation in periodic cylinder magnetoelectroelastic composite structures is studied using the plane wave expansion method. The band structure characteristics of magnetoelectroelastic rods embedded in polymer matrix and the reverse case are investigated taking the electric, magnetic and mechanical coupling effects into account. The generalised eigenvalue equation is derived to analyse the in-plane and out-of-plane modes, respectively. The numerical calculations for both the cases with Kagome lattices are performed. The relation between the gap widths and filling fractions are discussed in detail. The effects of the magnetoelectricity on the band structures and widths of band gaps are analysed. The band gap characteristics are illustrated further and the results will be helpful to design such kind of composite structures.

Microbuckling Solution of Elastic Memory Laminates under Bending

Abstract: Elastic memory composite (EMC) can endure a much higher nominal bending strain than the ultimate strain of reinforced fibers. Experimental studies have confirmed that microbuckling and post-microbuckling response for compressively loaded fibers in the soft matrix are the primary deformation mechanism for EMC to realize a large bending deformation. However, classical buckling solutions developed for hard-matrix composites cannot effectively predict the microbuckling onset and post-microbuckling response of soft-matrix composites under bending. In this study, a simplified 1D solution is proposed by combining matrix shear energy with Timoshenko’s elastic foundation energy. Based on the experiment results of carbon-fiber/resin EMC laminates under bending, the new solution exhibits to be effective in predicting the microbuckling wavelength and the onset of critical compressive stress and strain. In addition, the location of neutral-strain surface and failure modes are also discussed.

Finite element method for analysis of band structures of phononic crystal slabs with Archimedean-like tilings

Abstract: In this paper, a finite element method based on the ABAQUS code and user subroutines is presented to evaluate the propagation of elastic waves in a phononic crystal slab with Archimedean-like tilings. Three systems composed of cylinders embedded in host materials in square, ladybug and bathroom lattices are considered. Complete and accurate band structures and transmission spectra are obtained to identify the eigenmodes and band gaps. We find that Archimedean-like structures can have some advantages over the traditional square lattices regarding the completeness of the band gaps and their position and width. Also, due to the same square primitive unit cell, the two Archimedean-like lattices have similar wave responses at lower frequencies. The results indicate that the finite element method is efficient and suitable for the band structure computation of the phononic crystal slabs with complex lattice structures.

Elastic band gaps of two-dimensional phononic crystals tunned by material parameters

Abstract: In this paper, the analysis begins with the basic wave equations and derives the material parameters directly determining band gaps of the mixed in-plane wave mode in a two-dimensional phononic crystal. These parameters include the mass density ratio, the shear modulus ratio and Poisson's ratios of the scatterer and host materials. The effects of these parameters on the band gaps are discussed for different filling fractions and lattice forms. Band gaps are calculated by the plane wave expansion method. The results show that the maximum band gap will appear at both large density ratio and shear modulus ratio; but band gaps may also appear in other situations depending on the filling fraction and lattice forms. It is also shown that neither acoustic impedance ratio nor wave velocity ratio can determine the band gap independently. The present analysis can be applied to artificially design band gaps.

Plane magneto-electro-elastic moduli of fiber composites with interphase

Abstract: In the present paper, closed analytical expressions and universal relations for the effective coefficients are given. Matrix and inclusions materials belong to symmetry class 6mm. It is remarkable that the analytical formulae derived for all effective properties have a simple form. The computational implementation is easy. Besides its theoretical importance, they can be used for checking the implementation of experimental, numerical and analytical models.

Band structures for different kinds of point defect in phononic crystal thin plates

Abstract: The purpose of this paper is to explore theoretically the band structures for different kinds of point defect in phononic crystal thin plates for square / triangle lattice using the improved plane wave expansion method combining with the supercell technique. The defect is created by several means such as changing the radius, the mass density, the elastic modulus, the geometric shape of one of the cylinders, etc. The phononic crystal thin plate is composed of parallel cylindrical inclusion of Al 2 O 3 embedded periodically in the Epoxy host. The results show that the defect modes existing in the first band gap are strongly dependent on the size and the mass density of the point defect for the two lattices. Elastic modulus point defect could not lead the generation of the defect bands for the square lattice. However, for the triangle lattice, the elastic modulus has some influences on the defect modes. With decreasing of the size of the defect, all defect bands move from the upper edge of the first band gap towards the middle and the edges of the first band gap almost remain unchanged as the defect size varies.

Grey system theory based default risk model of power clients

Abstract: To be clear of the default probability of electricity fees from power clients in advance and change the postmortem management mode to the preventive management mode, it would decrease the default risk greatly in the process of electricity sales in the utility. Based on the analysis of complicated reasons of default, the main elements whose effect on default are known, the risk model involved with feature variables of default is constructed with the theory of grey system predication. Next, using a grey cluster algorithm, we classified clients into different categories according to the prediction of theirs feature variables, which would be valuable reference for power company to subdivide the consumption market and make out distinguishing credit management strategy.

Influence of disorder on the defect states of a phononic crystal with a point defect

Abstract: The supercell-based plane wave expansion method is used to study the effects of random disorders on the defect states of a two-dimensional solid-solid phononic crystal with a point defect. Phononic systems with plumbum scatterers embedded in an epoxy matrix are calculated in detail. The radius disorder and location disorder are concerned. The influences of the disorder degree on the defect states for both anti-plane and in-plane wave modes are investigated and discussed. It is found that, with increase of the disorder degree, the frequencies and localization degree of the defect bands will change. The influence of the disorder on the defect states is more pronounced for the in-plane modes than for the anti-plane modes. Radius disorder has more influences on the defect bands than the location disorder does. The analysis of this paper is relevant to the assessment of the influences of manufacture errors on behaviors of elastic wave propagating in wave filters, as well as the tuning of the point defect states.

Calculation of energy bands of two-dimensional phononic crystals with a hexagonal lattice by using FDTD method

Abstract: A recently published rectangular unit cell based finite difference time domain (FDTD) method used to calculate the energy bands of perfect two-dimensional (2D) photonic crystals (PTCs) with a hexagonal lattice, is further extended by the authors to the calculation of the energy bands of 2D phononic crystals (PNCs) with a hexagonal lattice. Numerical results show that accurate calculation of the energy bands of the perfect or defect-containing 2D PNCs with a hexagonal lattice can be given by using the rectangular unit cell or supercell based FDTD method.