Using a Smoothing Averaging Operator to Evaluate Macroscopic Parameters in Structurally Inhomogeneous Materials

A smoothing averaging operator is used in passing from structural to macroscopic modeling of the stress–strained state of an article from a composite material taking into account finite strains. A model is constructed using an integral operator, in which the macroscopic laws of conservation of energy and mass and the equation of motion have the ordinary form used to describe processes in homogeneous materials. As an example, macroscopic parameters are evaluated in a system consisting of an ensemble of inclusions in an infinite matrix.     

Integrated Stability-and-Vibration Study of Structurally Inhomogeneous Shells

The results of experimental studies into the stability and vibration of structurally inhomogeneous shells are generalized. The necessity for subsequent integrated investigations is substantiated     

小波加权残值法在斜板后屈曲上的应用

将斜板在大挠度理论下的平衡方程和变形协调方程转化为斜坐标系下的表达式,并无量纲化,对于四边固支斜板,选用尺度小于1的二维bior3.1重构尺度函数与小波作试函数,满足板在平面外的几何与自然边界条件,利用小波-Galerkin法将板的无量纲平衡控制方程与变形协调方程转化为两个非线性方程组,从而将后屈曲路径的求解转化为两非线性方程组的求解问题.以载荷作为迭代步长,采用Newton-Raphson迭代算法求得承受单向压缩四边固支斜板在不同边长比、不同斜角下的后屈曲平衡路径及四级渐近解.     

小波变换理论在损伤探测中的应用

本文采用小波变换技术，对含边裂纹的悬臂梁受冲击载荷作用的情况进行分析。根据电测法得到的动态应变的实验结果，用Morlet小波变换处理，能够很好地确定边缘缺陷的特性。这为结构损伤检测提供了一个很有效的方法，具有广阔的工程应用前景。     

可变形多孔介质渗透系数的测定方法

在Ｂｉｏｔ理论基础上给出可变形多孔介质耦合渗流基本方程；求出小试件一维定常耦合渗流问题的解答；表明在一维流固耦合情况下试件内部压力梯度有明显的非均匀性。因此通过实验确定可变形多孔介质渗透系数在数学上可归结为微分方程的反问题，传统的测试渗透系数的方法需要改进。介绍了可变形多孔介质渗透系数的测试原理和测试方法。对粒状多孔材料实验的结果表明，传统实验方法得到的渗透系数误差较大。     

Wavelet Analysis of Structures: Statics, Dynamics and Damage Identification

Applications of the wavelet transform in solid mechanics are presented herein. The analysis problem is addressed first where the objective is to derive an adaptive wavelet-based method for the static and dynamic analysis of structures. This is done via a collocation scheme. The damage identification problem is investigated next making use of the space-localized properties of the wavelet transform: the regularity of the solution is detected by looking at the amplitude of the coefficients of the wavelet decomposition of the response. Open problems are finally outlined that will be the object of future work.     

Finite-Amplitude Inhomogeneous Plane Waves of Exponential Type in Incompressible Elastic Materials

It is proved that elliptically polarized finite-amplitude inhomogeneous plane waves may not propagate in an elastic material subject to the constraint of incompressibility. The waves considered are harmonic in time and exponentially attenuated in a direction distinct from the direction of propagation. The result holds whether the material is stress-free or homogeneously deformed. This revised version was published online in August 2006 with corrections to the Cover Date.     

On a Displacement Based Solution to an Antiplane Crack Problem for Inhomogeneous Anisotropic Elastic Materials

This paper employs a displacement based method to examine an antiplane crack problem for an inhomogeneous elastic material in which the elastic moduli vary continuously with the spatial coordinates. Expressions for the crack tip stress intensity factors and the crack displacement are obtained in terms of Chebyshev polynomials. Numerical results are obtained for some particular inhomogeneous elastic materials.     

小波分析用于陀螺仪漂移测试信号分析的研究

为建立陀螺仪漂移特性模型，需对其进行测试。由测试得到的数据是含有噪声的，且一般是非平稳的，用小波分析测试数据是一种很有效的方法。在简述小波分析中的多分辨分析理论的基础上，用其对某型陀螺仪的实测数据进行了分析－预处理，其结果证实了所研究方法的有效性。     

转子裂纹识别仿真研究中的小波时频分析方法

谐波共振是识别转子裂纹的重要依据，但由于转子裂纹的弱激励、非线性、非平称稳等特性，导致利用传统信号处理方法不能准确有效地获取系统的谐波共振特性，从而难于识别出裂纹；小波时频分析方法是处理非线性、非平稳信号的强有力工具，将小波时频分析方法引入到裂纹识别的仿真研究中，基于建立的裂纹转子动力学模型，分析了利用小波时频分析方法识别裂纹的可行性。偏心激励转子裂纹故障识别的仿真研究表明了该方法的有效性。     

Stress Analysis of Anisotropic Inhomogeneous Shells of Revolution Subjected to Centrifugal Forces

An approach is proposed to analyze the stress state of thin shells of revolution under centrifugal loads with regard for anisotropy, the meridional variability of geometrical and mechanical parameters, and the eccentricity of the axis of revolution relative to the axis of geometric symmetry. Allowance is also made for the change in the dimensions of the shell due to deformation, which results in a nonaxisymmetric distribution of stresses and strains and their nonlinear dependence on the squared frequency of rotation. By separating variables, the problem is made one-dimensional and then solved numerically. The stress state of an ellipsoidal filament-winded composite shell is analyzed     

Stress State of Non-Thin Nearly Circular Cylindrical Shells Made of Continuously Inhomogeneous Materials

International Applied Mechanics - The stress state of dented circular non-thin cylindrical shells under certain boundary conditions at the ends is analyzed. The shells are made of continuously...     

基于小波包能量特征的薄膜涂层材料界面缺陷检测法

目前国际上对薄膜涂层界面缺陷尚缺乏有效的探伤方法.本文基于薄膜涂层材料中波传播的模型,考察了在涂层表面施加冲击脉冲激发表面波,测取涂层表面各点的动态特性,结合波形分析技术进行界面缺陷检测的可行性.通过有限元模拟分析产生脉冲载荷并且激发表面波,对涂层表面接收的加速度波响应信号进行小波包数学变换,提取小波包相对能量谱变化率指标,发现加速度信号的小波包相对能量谱变化率指标在存在界面缺陷的区域有显著的变化,并且在缺陷中心区域效果最明显,而且该指标对不同薄膜厚度界面缺陷的具有敏感性,可以通过该指标较准确的判断裂纹的位置和尺寸.此项研究可以为开发薄膜涂层界面缺陷的无损检测方法提供一定的理论基础.     

基于小波分析的条纹图滤波方法

本文提出了一种新颖的干涉条纹图非线性滤波方法,可以选择性地在频域图像的不同区域选用不同的滤波方式,在滤掉图像中大部分散斑噪声的同时,能够减少信息的损失,使图像的内部边界仍然保持清晰。文中首先简介了正交小波变换的原理,然后介绍了去除散斑噪声的具体算法,最后给出了计算机模拟去噪声的结果     

Transition of Shock-Loaded Metals to a Structurally Unstable State

The transition of M3 copper to a structurally unstable state was studied in a series of experiments with shock loading under uniaxial deformation conditions. The threshold strain rate was determined at which the motion of the structurally unstable material reaches an equilibrium regime of energy exchange between the mesoscale and the macroscale — the so-called Kolmogorov statistical equilibrium regime. The notions of the representative volume and elementary pulse of energy exchange between the mesoscale and macroscale are introduced. Visualization conditions of localized-shear bands and rotation structures are found by optical, scanning, and transmission electron microscopy.     

Stress Analysis of Rotating Inhomogeneous Transversely Isotropic Hollow Spheres

An approach is proposed to the stress–strain analysis of hollow, arbitrarily inhomogeneous, transversely isotropic, either closed or open spheres that rotate about the axis of symmetry with a constant angular velocity. The stress problem for a rotating single-layer sphere and a segment of a sphere is solved as an example. The distribution of radial stresses and displacements along the radius of the sphere is analyzed depending on thickness variation at arbitrary points of the sphere     

基于连续小波变换的风速时程特性识别与分析

由于风速时程属于频域宽和频率变化剧烈的时变信号,需用具有良好时频局部化特性和弹性时．频窗口的小波变换进行分析。本文的目的是在风速时程的描述上较全面地了解风速的时频特性。利用小波分析方法在时域和频域的良好局部化性质,聚焦到风速时程的任意细节并加以分析,快速、准确地提取样本的局部谱密度特征,特别是对在整个时程记录中,具有相同功率谱但时频内容有差别的风速时程。用小波变换分析试验得到的风速时程,并研究和识别试验得到的曲线和实测风速曲线的时频特性、能量关系和局部谱密度特征。     

一种新的小波及其在结构损伤检测中的应用

结构受冲击将引起某些部位的震荡、裂纹甚至断裂,从而导致结构刚度下降.此时振动信号会出现奇异性或携带突变信息,而这些突变信息反映了结构的损伤情况.加之冲击信号测试环境一般较为复杂,环境噪声对测试存在一定的影响.然而,利用合理的小波变换技术去噪可以识别出损伤情况.本文通过对冲击振动的信号特性进行分析构造了一种新的基本小波,并论证了该小波的基本特征.最后运用小波分析的信号奇异检测理论结合实例将该小波用于冲击振动仿真分析中.计算结果表明,利用该小波进行结构损伤信号分析能清晰地识别结构损伤的时刻.采用该小波函数的构造方法,可避免通常采用Daubechies系列小波作为信号分析而要繁琐地选择不同小波函数的过程.     

Numerical Analysis of Stationary Dynamic Processes in Anisotropic Inhomogeneous Cylinders

Efficient numerical-analytical approaches are proposed for analyzing stationary dynamic processes. The approaches are used to study the propagation of elastic waves in anisotropic inhomogeneous cylinders with circular and noncircular cross sections and the natural vibrations of anisotropic solid and hollow cylinders of finite length with different end conditions. The dependence of the dynamic characteristics of cylinders on their geometrical and mechanical parameters is analyzed __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 8, pp. 3–40, August 2005.     

The Effects of Compressibility on Inhomogeneous Deformations for a Class of Almost Incompressible Isotropic Nonlinearly Elastic Materials

Experimental data for simple tension suggest that there is a power–law kinematic relationship between the stretches for large classes of slightly compressible (or almost incompressible) non-linearly elastic materials that are homogeneous and isotropic. Here we confine attention to a particular constitutive model for such materials that is of generalized Varga type. The corresponding incompressible model has been shown to be particularly tractable analytically. We examine the response of the slightly compressible material to some nonhomogeneous deformations and compare the results with those for the corresponding incompressible model. Thus the effects of slight compressibility for some basic nonhomogeneous deformations are explicitly assessed. The results are fundamental to the analytical modeling of almost incompressible hyperelastic materials and are of importance in the context of finite element methods where slight compressibility is usually introduced to avoid element locking due to the incompressibility constraint. It is also shown that even for slightly compressible materials, the volume change can be significant in certain situations.