有单面粘弹负载层时各向同性薄板中的SH波传播

1.引言 随着现代工业的发展,SH波传感检测成为在线检测板状构件的有力手段,人们在理论和实验上都对SH波的传播做了很广泛的研究.粘弹材料的应用也越来越广泛,现实生活中的很多材料都具有粘弹特性,由于媒质衰减的存在,使得我们不能将这些材料近似作为弹性材料考虑.这使我们有必要讨论和研究粘弹材料中的声传播特性和它的传感特性[3].     

有对称液层负载时各向异性板中Lamb波的传播

1　引　言　　 L amb波是固体薄板中传播的一种弹性波 ,最初有关 Lamb波的微传感的理论研究大都只局限在各向同性板材中 ,由于在各向异性压电板上可以高效激发 L amb波 ,灵敏度高 ,体积小 ,性价比高等特点 ,因而各向异性材料有更大的实用性 ,实验上已有各向异性压电板传感器的尝试 [1] ,特别是在生物传感领域 ,由于能检测到病毒等 ,因而特别具有吸引力。在理论上 S.G.Joshi[2 ] ,Chimenti[3 ] ,Vinay Day-al[4 ] 都对各向异性板中的 L amb波进行了理论推导和数值计算 ,为了对各向异性材料微传感性的机理有进一步深入了解 ,本文研究若干…     

各向异性弹性层中SH波传播的边界元方法

本文利用坐标变换下的映象法求出了底部为刚性边界的各向异性弹性层中SH波传播问题的格林函数,并由此建立了求解分层介质问题的边界元方法。文中给出了在稳态线荷载作用下带有圆孔的弹性层中反应的计算实例。     

正交各向异性空心圆柱体的周向SH波

基于线性三维弹性理论,得到了正交各向异性管道中位移表示的周向波控制方程.波动方程中的轴向位移独立于其它两个方向.即波的传播可以分解为SH波和类Lamb波.通过贝塞尔函数求得了这个周向SH波频散方程.方程中决定周向SH波特性的弹性常数有两个,一个决定了波的频率,另一个决定了波速.最后分别讨论了两个弹性常数和波数变化对周向SH波位移模式的影响.     

压电复合材料层合结构中的SH波

考虑压电耦合效应,通过传递矩阵-二维谱分析研究了压电复合材料层合板稳态SH波的频散特性和瞬态SH波的传播特性。数值分析表明: 压电耦合作用提高了SH波的截止频率和相速度; 由表面扰动激发的SH波, 一部分能量向板深度方向传播, 一部分以表面波的形式在两倍波长深度内传播。所采用的传递矩阵-二维谱分析为层合结构瞬态波动研究提供了一种有效的数值方法。      

压电弹性层合梁-板结构中SH波的传播

建立了压电层合梁-板结构的压电-弹性动力学基本方程式，在给定压电层合梁-板结构形式和波传播方向的情况下，对基本方程式进行了简化；利用连续性条件和边界条件，建立了波传播的特征方程式，并对波动方程式进行求解；得到了前三阶频散关系曲线。通过实例数值计算，讨论了弹性层、压电层的厚度比与频散关系的影响，得出了SH波在压电层合梁-板结构中传播的基本特性。     

功能梯度压电层/压磁半空间结构中SH波传播

分析功能梯度压电层/压磁半空间结构中SH波传播特性。功能梯度压电材料沿x2方向按指数形式变化,电学边界条件分为电学短路及开路,基于推导的频散方程数值分析功能梯度压电材料的梯度系数、覆层厚度及边界条件对频散关系影响。研究成果可为研制、设计高性能声波器件提供理论参考。     

粘弹正交各向异性空心圆柱体周向SH波

基于Kelvin-Voight模型,推导了粘弹正交各向异性空心圆柱体周向SH波控制方程,得出了SH波特性受两个弹性常数与粘性系数的影响。通过第一类和第二类Bessel函数,求出频散方程。计算了四种不同径厚比下的相速度频散曲线和衰减曲线,分析了径厚比的变化对频散和衰减曲线的影响。为了与正交各向异性相比较,计算了粘弹各向同性空心圆柱体中周向SH波,并讨论了两个弹性常数和粘性系数对频散曲线和衰减曲线的影响。     

一种新型SH波传播特性研究

1.引言 Michio Kadota等于2001年首次提出了一种在 ST-90°X石英基片上利用重金属制成的叉指换能器与反射栅而激发的一种新型剪切(SH)波.这种波具有较大的机电耦合系数和反射系数,良好的频率温度特性.Michio Kadota等人已经将这种SH波应用于实现一种小型化的谐振器式滤波器[1][2] [3],取得了好的实际效果.Michio Kadota等人是利用Campbell的方法对这种波的传播特性即传播速度以及机电耦合系数来进行分析与求解的[4],这种方法比较烦琐,也不利于进一步扩展其应用,研究其特性.本文利用层状介质中波的传播的方法求解[5],求解过程简单准确.本文给出了求解的过程以及计算结果,并与前人的计算结果进行了对比,结果表明了其较好的一致性.     

固体板中SH型板波的二阶和频积累波发生

当各向同性固体板中传播的ＳＨ型板波模式饱含两个频率成分时,板材的非线性将导致二阶和频及差频声波的发生。本文在二阶近似条件下对此问题进行了研究,得到了如下结论：１）二阶差频声波不具有随传播距离积累增长的性质;２）两个ＳＨ型板波模式的阶数和频率满足一定关系时,二阶和频声波可以个具有积累增长的性质;３）二阶和频积累波声场呈对称性质。本文还给出满足边界条件和初始条件的二阶和频各累波解的解析表达式。     

Numerical calculations of elastic wave propagation in anisotropic thin films deposited on substrates

In this work, we present a generalized numerical model to study the dispersion curves of elastic waves in anisotropic thin layer/substrate systems. Dispersion curves as a function of wave frequency for different propagation angles are calculated. The nature of the mode (Rayleigh or Love) is identified by analyzing the polarization of the three-dimensional displacement field. This numerical model has been applied to the system Au(0 0 1)/Ni(0 0 1).     

SH wave propagation in piezoelectric coupled plates

The propagation of shear horizontal (SH) wave in a piezoelectric coupled plate is investigated in this paper. Full account is taken of the piezoelectric coupling effect to the isotropic metal core in the mathematical model. One of the applications of this research is in the damage detection of the host metal structure from the wave propagation signal excited by the piezoelectric layer which is surface bonded on the surface of a metal core. This research is distinct from the previous works on SH propagation in piezoelectric structures because the piezoelectric materials were used as the core structure in the previous studies, and the potential of the studies was mainly on time-delay devices. The dispersive characteristics and the mode shapes of the transverse displacement and the electric potential of the piezoelectric layer are theoretically derived. The results from numerical simulations show that the phase velocity of the plate structure tends to the bulk shear wave velocity of the host metal core at high wave number when the shear wave velocity of host plate is larger than that of PZT bonded on it. Furthermore, there are three asymptotic solutions of wave propagation when the shear wave velocity of the host plate is smaller than that of PZT. The mode shape of the electric potential of the piezoelectric layer changes from the quadratic shape at lower wave number and with thinner piezoelectric layer to the shape with more zero nodes at higher wave number and with thicker piezoelectric layer. These findings are significant in the application of wave propagation in piezoelectric coupled structures     

The propagation of Love waves in a fluid-saturated porous anisotropic layer

Summary The paper concerns the propagation of Love waves in a transverse-isotropic fluid-saturated porous layer overlaying an elastic nonhomogeneous half-space. Using the Biot's theory for the porous layer and the theory of elasticity for the lower medium, the dispersion equation has been derived. This complex transcendental equation that relates frequency, phase velocity, anisotropy factor of the layer and the inhomogeneity character of the half-space has been solved with the aid of successive approximation method. The effect of anisotropy and heterogeneity has been shown graphically.With 2 Figures     

SH wave propagation in a cylindrically layered piezoelectric structure with initial stress

Summary SH wave propagation in a cylindrically layered piezoelectric structure with initial stress is investigated analytically. By means of transformation, the governing equations of the coupled waves are reduced to Bessel and Laplace equations. The boundary conditions imply that the displacements, shear stresses, electric potential, and electric displacements are continuous across the interface between the layer and the substrate. The electrically open and short conditions at the cylindrical surface are applied to solve the problem. The phase velocity is numerically calculated for the electrically open and short cases, respectively, for different wavenumber and thickness of the layer. The effect of the initial stress on the phase velocity and the electromechanical coupling factor are discussed in detail for piezoelectric ceramics PZT-5H. We find that the initial stress has an important effect on the SH wave propagation in the cylindrically layered piezoelectric structures. The results also show that the ratio of the layer thickness to the wavelength has a remarkable effect on the SH wave phase velocity and electromechanical coupling factor.     

Two-dimensional wave propagation in a micropolar thermo-elastic layer with stretch

This paper deals with the propagation of 2-dimensional waves in a thermo-elastic micropolar solid layer which can stretch and contract. Thermo-elastic Rayleigh wave velocity equation in the micropolar medium with stretch has been deduced from the above theory. The wave velocity equation obtained is in agreement with the classical result of Rayleigh when the layer is unstretched and thermal and micropolar effects are negligibly small.     

Transient wave propagation in a viscoelastic sandwich plate

Summary This paper examines the propagation of coupled P and S waves in a three layer sandwich plate consisting of a viscoelastic core bounded by identical elastic outer layers. The waves are initiated by an impulsive normal line load applied to the upper surface of the plate. The response of the top surface is computed for various values of the creep and relaxation time constants of the core. The results indicate that, for some values of the time constants, the viscoelastic core provides effective damping of the transients, while for others the damping is virtually non-existent. In each case the dominant contribution to the far-field solution comes from the Rayleigh wave.     

Evolution of high-frequency ground-penetrating radar direct ground wave propagation during thin frozen soil layer development

High frequency ground-penetrating radar direct ground waves were used to monitor the seasonal development of a thin, high velocity frozen soil layer over a wet low velocity unfrozen substratum. During the freezing process, the progressive attenuation of a low velocity direct ground wave and the subsequent development of a high velocity direct ground wave were observed. Numerical simulations showed that low velocity direct wave event occurring after freezing commences is due to energy leaking across the frozen layer from the spherical body wave in the unfrozen half space. This leaky phase progressively dissipates until the frozen layer reaches a thickness equivalent to one quarter of the dominant wavelength in the frozen ground. The appearance of the high velocity direct wave is governed by its destructive interference with the reflection events from the base of the frozen layer. This interference obscures the high velocity direct wave event until the frozen layer thickness reached one half of the dominant wavelength in the frozen ground. These changes in direct wave transmission permit frozen layer monitoring for thicknesses that are significantly less than those feasible using the reflection event from the frozen–unfrozen boundary.     

Conditions of heat contact of anisotropic bodies via a thin anisotropic layer

Pidstryhach Institute of Applied Problems in Mechanics and Mathematics, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 6, pp. 86–88, November – December, 1994.