Interfacial debonding of two-phase composite with periodic structure

A mixed analytical-numerical (boundary element method) procedure is presented for estimating the effective elastic moduli of a two-phase periodic composite by application of a unit cell. The two-phase composite consists of a metal/polymer matrix and one/three circular ceramic inclusions with adhesive and partial debonding of the interface. The results are displayed numerically with special attention given to development of plastic zones as debonding occurs. Dependence of load-time history is exhibited.     

考虑剪切效应层合板的Hamilton体系及辛几何方法

基于ＹＮＳ层合板理论,通过对混合能变分原理的修正,建立了层合板问题的Ｈａｍｉｌｔｏｎ正则方程。在辛几何数学框架下,采用共轭辛正交归一关系给出精确解。并与经典层板理论进行了比较。     

非协调四结点平面等参位移元新列式方法

本文导出一种等参协调元位移函数的新的表示方法,在此基础上建立起了构造等参非协调元的新方法。作为实例,构造出两个可以给出单刚显式的四结点平面非协调新单元。     

GENERALIZED REVERBERATION MATRIX FORMULATION FOR WAVE PROPAGATION IN MULTILAYERED MEDIUM

<正>Generalized reverberation matrix(GRM)formulation is presented to investigate elastic wave propagation in a complex multilayered solid by the combination of reverberation-ray matrix(RRM)method and stiffness matrix(SM)method.RRM method formulates a reverberation matrix,which reflects the reflection or refraction of the elastic waves in the multilayered solid.However,the dimension of RRM increases as the sublayer number increases,which may result in lower calculation efficiency of the generalized rays.SM formulation yields a system matrix of the constant dimension to promise higher calculation efficiency,but it is difficult to identify the generalized rays.In order to calculate the generalized rays in the complex multi-layered solid efficiently,the RRM formulation is applied to the interested sublayer for the evaluation of the generalized rays and SM formulation to the other sublayers,to construct a generalized reverberation matrix of the constant dimension,which is independent of the sublayer number.Numerical examples show that GRM formulation has higher calculation efficiency for the generalized rays in the complex multilayered-solid configuration compared with RRM formulation.     

TRANSFER MATRIX METHOD FOR ANALYZING VIBRATION AND DAMPING CHARACTERISTICS OF ROTATIONAL SHELL WITH PASSIVE CONSTRAINED LAYER DAMPING TREATMENT

The first order differential matrix equations of the host shell and constrained layer for a sandwich rotational shell are derived based on the thin shell theory.Employing the layer wise principle and first order shear deformation theory, only considering the shearing deformation of the viscoelastic layer, the integrated first order differential matrix equation of a passive constrained layer damping rotational shell is established by combining with the normal equilibrium equation of the viscoelastic layer.A highly precise transfer matrix method is developed by extended homogeneous capacity precision integration technology.The numerical results show that present method is accurate and effective.     

快速小波边界元的矩阵后压缩方法

介绍了一种基于传统边界元单元划分的小波 Galerkin 边界元法,该方法具有几乎线性(即 ON,N 为自由度)的求解复杂度。在准消失矩小波的框架下介绍了非标准型系数矩阵的压缩问题,提出了一种后压缩算法以降低小波边界元法的内存消耗。求解 Stokes 方程的算例表明,后压缩算法在保证结果收敛特性的情况下可以将系数矩阵的内存占用量降低 5 倍以上。     

On the stability and dissipation of wall boundary conditions for compressible flows

Characteristic formulations for boundary conditions have demonstrated their effectiveness to handle inlets and outlets, especially to avoid acoustic wave reflections. At walls, however, most authors use simple Dirichlet or Neumann boundary conditions, where the normal velocity (or pressure gradient) is set to zero. This paper demonstrates that there are significant differences between characteristic and Dirichlet methods at a wall and that simulations are more stable when using walls modelled with a characteristic wave decomposition. The derivation of characteristic methods yields an additional boundary term in the continuity equation, which explains their increased stability. This term also allows to handle the two acoustic waves going towards and away from the wall in a consistent manner. Those observations are confirmed by stability matrix analysis and one‐ and two‐dimensional simulations of acoustic modes in cavities. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamics of structural interfaces: Filtering and focussing effects for elastic waves

Dynamics of thick interfaces separating different regions of elastic materials is investigated. The interfaces are made up of elastic layers or inertial truss structures. The study of evanescent mode propagation and transmission properties reveals that the discrete nature of structural interfaces introduces unusual filtering characteristics in the system, which cannot be obtained with multilayered interfaces. An example of metamaterial is presented, namely, a planar structural interface, which acts as a flat lens, therefore evidencing the negative refraction and focussing of elastic waves.     

二次特征矩阵表示的特征值有界性分析

采用二次特征矩阵近似表示精确有限元和精确动态子结构分析中得出的超越或非线性动态刚度阵，并证明了在满足一定条件的前提下，二次特征阵给出的特征值是精确刚度阵特征值的上界或下界。     

EVOLUTION OF THE MICROCRACKS IN WHISKER TOUGHENING CERAMIC MATRIX COMPOSITES

The modified equivalent inclusion theory by the authors and the internalvariable theory are employed to investigate the evolution of the microcracks in whiskertoughening ceramics and the influence of the microcracks on the mechanical propertiesof the material. The effect of residual thermostrain, whisker content and aspect ratio isconsidered. The modulus, initial nonlinear load, strength and nonlinear constitutiverelation are calculated and some important conclusions are given.