超薄层状复合媒质弱界面深度与声导波

结合推导层状复合媒质各界面刚性联接时声导波频散特性方程的传递矩阵方法,以及滑移界 面边界条件和弱界面“弹簧”模型,分别导出了超薄层状复合媒质中存在不同深度弱界面、滑移界面和脱层情况下声导波的广义频散方程,分析了三种联接界面的深度对低模式声导波频散特性的影响. 关键词： 导波 界面 频散     

弱界面固体附层媒质中的类Rayleigh波

当半无限大固体媒质上有一层固体附加层时表面波是频散的。由界面的“准弹簧”模型,本文导出了有各向同性固体附加层时半无限大各向同性均匀媒质中弱界面情况下的类Ｒａｙｌｅｉｇｈ波的特征方程。文中给出了典型复合结构具有刚性联接界面、滑移联接界面和弱界面时类 Ｒａｙｌｅｉｇｈ波的色散曲线,分析了界面刚度系数对类 Ｒａｙｌｅｉｇｈ波传播速度的影响。数值计算的结果表明选择合适的参数可以由低频超声类Ｒａｙｌｅｉｇｈ进行涂层结构界面特性的无损评价。     

弱界面压电覆层复合结构中的声导波

建立压电覆层复合结构中声导波传播模型,结合弱界面“弹簧”模型,推导了压电覆层复合结构存在刚性、滑移联接界面等几种不同界面条件下声导波的广义频散方程,数值计算钛锆酸铅基压电陶瓷覆层复合结构在不同界面条件下声导波的频散曲线,分析了界面特性对导波传播相速度的影响。数值计算和分析表明为了能够有效地评价界面的特性,选择合适的声波模式和声波频率是非常重要的。实验结果验证了界面假设的有效性,为进一步深入研究以多模式声导波参量为基础的压电覆层复合结构界面特性参数反演方法提供了理论基础。     

层状各向异性固体媒质的声反射和声透射

本文导出了联系任意对称的各向异性固体层上下界面力学量（位移和应力）的传递矩阵，从而提出了层状固体媒质声反射和声透射的一般模型，作为例子，本文数值计算了金属铝中双层正交对称固体（其间界面呈刚性联接或滑移联接）对声波的反射和透射系数。     

横向各向同性柱状复合结构对超声波的散射

首先描述了横向各向同性复合圆柱结构的入射声场、散射声场及内部的驻波声场，然后利用转移矩阵方法导出了求解散射声场的方程组，计算了铝／各向异性界面层／纤维复合结构对斜入射声波的背向散射谱和散射截面积。将柱状复合结构中各向异性界面薄层相应的转移矩阵作渐近展开，建立了模拟这种界面薄层的弹簧模型及界面处广义边界条件。结果表明，模型中劲度常数仅依赖于界面薄层厚度及界面层媒质的弹性常数Ｃｌｌ，Ｃ１２和Ｃ４４，而振子质量与Ｃｌｌ，Ｃ４４，Ｃ１３和Ｃ３３有关。     

脱粘缺陷对粘接结构频散特性的影响

采用全局矩阵理论,通过引入内聚强度弱化模型和弹簧模型,计算了脱粘缺陷对粘接结构频散特性的影响。分析了内聚强度缺陷、界面缺陷及混合缺陷等因素对粘接结构频散特性的影响,发现频散曲线的演化规律与材料声学性质密切相关。不同材料和不同组合,其规律有很大不同。针对各向同性粘接结构,可能通过考察特定频率段内频散模态的变化,实现对脱粘缺陷的检测。     

具有弱界面的柱状复合结构中轴对称声导波

利用柱状分层结构中轴对称声导波的波动方程和界面“弹簧”模型，导出了具有弱界面的双层柱状复合结构中轴对称声导波的广义色散方程，计算了刚性联接和滑移联接界面时双层复合管(腔壁为自由界面或腔内充水)和双层复合棒中轴对称声导波的色散特性，分析了弱界面的轴向劲度系数对低阶轴对称声导波的影响- 关键词：     

具有刚性联接界面和滑移界面的层状固体媒质的声反射

利用矩阵方法,本文提出了声波从具有刚性联接和滑移界面的层状固体媒质反射特性的一般模型,导出了包含一个或两个滑移界面的层状固体媒质纵波和横波声反射系数解析表达式。文中还给出一些典型粘接件声反射系数的数值计算结果,为正确选择超声评价这些界面特性所采用的技术参数提供了依据。     

基底上覆分层薄膜超声Scholte波特性与薄膜定征

分层薄膜-基底结构广泛应用于微电子器件等诸多领域,但薄膜材料参数超声测量尤其是横波速度的定征是一个困难的问题。本文对液固界面Scholte界面波的频散特性和脉冲激励的声压响应进行了理论分析。结果表明,液固界面Scholte波频散与分层膜-基底结构的速度分布密切相关。薄膜材料各层的厚度和横波速度对界面波频散特性有显著影响。基于Scholte界面波的频散特性,提出了一种多层膜的多参数反演定征方法。首先针对理论信号进行薄膜参数反演,验证了该方法的可行性。后续对不同类型的多层膜材料样品进行了液固界面波激发与采集实验,实验信号的薄膜参数反演结果进一步验证了该方法的可行性和有效性。     

考虑界面状况时柱状弹性固体的声波散射

导出了求解母材料固体中镶嵌的柱状弹性固体(两固体间存在界面薄层)声波散射系数的一般表达式.根据Flax的共振散射理论,对背向散射谱中的共振模式进行了识别.利用模拟界面薄层的弹簧模型,考察了界面层切向劲度常数K_T对共振模式形态的影响 关键词： 声波散射 共振模式 界面     

LAMB WAVE MODES IN A TWO-LAYERED SOLID MEDIUM WITH A WEAK INTERFACE

Using the "spring" model for a weak interface between two solids, we derive the charac-teristic equation for the Lamb waves in a two-layered solid composite and make numerical computations for dispersion curves in an aluminum/copper structure with a rigid or slip interface. The influence of the shear stiffness of the interface on the low order Lamb wave modes is considered.     

Stable reformulation of transfer matrix method for wave propagation in layered anisotropic media.

The numerical instability problem in the standard transfer matrix method has been resolved by introducing the layer stiffness matrix and using an efficient recursive algorithm to calculate the global stiffness matrix for an arbitrary anisotropic layered structure. For general anisotropy the computational algorithm is formulated in matrix form. In the plane of symmetry of an orthotropic layer the layer stiffness matrix is represented analytically. It is shown that the elements of the stiffness matrix are as simple as those of the transfer matrix and only six of them are independent. Reflection and transmission coefficients for layered media bounded by liquid or solid semi-spaces are formulated as functions of the total stiffness matrix elements. It has been demonstrated that this algorithm is unconditionally stable and more efficient than the standard transfer matrix method. The stiffness matrix formulation is convenient in satisfying boundary conditions for different layered media cases and in obtaining modal solutions. Based on this method characteristic equations for Lamb and surface waves in multilayered orthotropic media have been obtained. Due to the stability of the stiffness matrix method, the solutions of the characteristic equations are numerically stable and efficient. Numerical examples are given.     

EFFECT OF INTERFACE LAYER ON LAMB WAVE PROPAGATION IN SOLID ADHESIVE JOINTS: A PERTURBATION MODEL

This paper presents a perturbation model for calculating the approximate Lamb wave velocities in solid adhesive joints. The numerical computations show that the approximate values of the Lamb wave velocities are very close to the exact ones if the thickness of the interface layer is small. A comparison of the perturbation analysis with the approximate "spring" model is given. The significance of the perturbation model is discussed for the inverse deduction of the mechanical properties of the interface layer from Lamb wave measurements.     

INHOMOGENEOUS WAVES IN ANISOTROPIC POROUS LAYER OVERLYING SOLID BEDROCK

The problem of propagation of inhomogeneous waves in anisotropic porous layered medium is studied using transfer matrix. Firstly, transfer matrix for an anisotropic porous layer is derived. Biot's poro-elastic theory is incorporated to model the acoustics of anisotropic porous layer. The interface between porous layer and elastic half-space is considered as imperfect and modified boundary conditions are applied for this more realistic situation. The theory of transfer matrix is used to derive the analytical expression for the surface impedance. Numerical computation of results is done for different degrees of bonding in the low as well as high-frequency range. In the first case, which is relevant to geophysical studies, the surface impedance is predicted for low-frequency range and surface impedance for second model is computed in high-frequency range. It is observed that loose bondedness is accompanied by the loss of energy at the interface. The technique of transfer matrix is utilized to compute the surface impedance in both cases. The role of surface impedance in seismological studies and in the study of composites is discussed.     

Lamb wave sensors array for nonviscous liquid sensing

The interdigital transducer (IDT) can excite Lamb wave in a piezoelectric plate loading with a liquid layer, and the phase velocity of Lamb wave is associated with the properties of the liquid layer. In this paper, the concept of effective permittivity is introduced to study the Lamb wave’s potential application in liquid sensing. Considering the measuring of ideal nonviscous liquid, the sensors array is designed to sense the density and the dielectric constant of the liquid layer simultaneously. Using LiNbO₃ as piezoelectric material, in order to improve the sensors array sensitivity and the electro-mechanical coupling coefficient, the optimized results including plate thicknesses and cut orientations are presented by numerical simulation. These studies show that the Lamb wave sensors array can be potential in liquid sensing.     

Study on laser-generated Lamb waves propagation in viscoelastic and anisotropic plate

The propagation characteristics of laser-generated Lamb waves in thin composite plates are theoretically studied. Taking the anisotropic and viscoelastic properties of the composite material into account, the finite element models for simulating laser-generated Lamb waves in the composite material are established in the frequency domain. Numerical results are calculated in purely elastic and viscoelastic transversely isotropic plates, respectively. The effects of the anisotropic and viscoelastic properties on the propagation of Lamb waves are analyzed in detail. The numerical results exhibit that the features of the laser-generated Lamb wave, including attenuation, velocity, frequency, and the dispersive nature, have a close relationship with the anisotropic and viscoelastic properties of the material.     

钢-混凝土结构弱粘接界面缺陷的超声导波检测*

钢-混凝土结构是土木工程中的一种常用结构形式,钢与混凝土粘接处可能出现弱粘接甚至完全脱粘的缺陷,严重影响结构的安全性。该文提出利用空气耦合超声导波衰减的方法实现钢-混凝土结构粘接状态的非接触无损检测方法,分析不同厚度粘接界面对超声导波衰减的影响。基于全局矩阵技术对钢-混凝土结构求解理论频散方程和衰减曲线,得到界面层不同粘接条件下的理论参数及衰减特性。建立不同粘接条件的有限元模型,定量分析不同模态对粘接缺陷的检测敏感度。研究界面层厚度分别为1 mm和2 mm两种情况下S0能量的衰减情况。研究结果表明:S0模态可有效判断粘接结构的粘接状态,对于同一界面层厚度,随着界面粘接条件变弱,S0最大幅值与A0最大幅值比不断增大;不同厚度同一粘接条件下,2 mm相较于1 mm该值更大。该方法在钢-混凝土结构粘接界面缺陷的检测方面具有良好的应用价值和发展前景。     

The measurement of A0 and S0 lamb wave attenuation to determine the normal and shear stiffnesses of a compressively loaded interface

Guided waves in an elastic plate surrounded by air propagate with very low attenuation. This paper describes the effect on this propagation of compressively loading an elastomer with high internal damping against one surface of the elastic plate. The propagation of both A0 and S0 Lamb modes is considered. The principal effect is shown to be increased attenuation of the guided waves. This attenuation is caused by leakage of energy from the plate into the elastomer, where it is dissipated due to high viscoelastic damping. It is shown that the increase in attenuation is strongly dependent on the compressive load applied across the solid-solid interface. This interface is represented as a spring layer in a continuum model of the system. Both normal and shear stiffnesses of the interface are quantified from the attenuation of A0 and S0 Lamb waves measured at each step of the compressive loading. The normal stiffness is also measured independently by normal incidence, bulk longitudinal wave ultrasound. The resulting predictions of wave propagation behavior, such as attenuation, obtained by the model are in excellent agreement with those measured experimentally.