粘接结构中垂直入射纵波的准静态模型解

研究了板状粘接结构中垂直入射纵波的准静态模型解。在将粘接界面简化为准静态模型（QSM）的情况下,推导了界面为完好连接且上下基体为同种材料的板状粘接结构中垂直入射纵波的声反射和透射系数表达式。首先将纵波的准静态模型解和精确解进行了比较以阐释准静态模型的适用条件;接着分析了法向刚度系数和界面相对质量的变化对纵波反射和透射特性的影响。结果表明,在特定频率下,随着刚度系数或界面相对质量的增加,纵波的反射和透射系数的幅值分别减小和增大至某一稳定值。研究成果可为实验时采用纵波垂直入射检测粘接结构提供一定的理论指导。     

板状粘接结构中对称和反对称纵波与界面的相互作用

为了激发粘接结构中的导波或界面波,通常需要将声波从两半无限介质同相位或反相位地同时入射多层系统。针对此问题,基于矩阵方法,推导了界面处于理想连接的情况下,对称或反对称纵波从上下半无限空间入射时,三层板状粘接结构中纵、横波的反射与透射系数表达式。分析了入射角度、粘接层厚度以及基体材料等对声波反射(或透射)特性的影响。结果表明,对称或反对称纵波垂直入射时不发生波型转换。粘接结构中声波的反射(或透射)特性与入射角度、频率以及粘接层厚度等参数密切相关。在相同的粘接层厚度(或频率)范围内,随着声波频率(或粘接层厚度)的增加,谐振频率曲线向低频漂移。该方法可作为粘接结构中体波或导波传播特性研究的重要理论基础。     

固体粘接界面的非线性共振特性研究

研究考虑粘接界面非线性的条件下,双层固体粘接薄板的振动特性。将双层板间的振动耦合看作一组非线性弹簧,理论上运用分离变量等数学方法,求解得到粘接层的应力应变关系为线性条件下的解析解,以及考虑非线性参量时系统共振的数值解。通过对双层铝板的环氧树脂粘接模型进行仿真研究分析,发现界面的共振频率随着界面粘接强度非线性参量的增加呈现先增大后减小的趋势,当界面强度弹性参量为300GN/m3时,共振频率的最大偏移量达到10%。在粘接强度退化早期,利用界面的非线性共振特性可以更好地检测粘接质量。     

固体间不同厚度界面层的超声反射

将固体间界面层模拟为固体或流体薄层，本文讨论了界面层对斜入射纵波和横波的反射和透射，测量了垂直入射纵波的反射系统随声波频率的两铜块之间水界面层厚度的变化。理论和实验结果基本符合。     

弱粘接界面固-固界面波特性及与界面粘接性质关系数值研究

根据两固体粘接结构在不同粘接强度下的弹簧模型边界条件,通过傅里叶积分变换方法进行波动方程求解,理论分析和数值计算了相近横波速度的两种固体间界面波的频散及衰减特性.计算结果表明,当切向弹簧劲度系数从滑移粘接界面向完好粘接界面逐渐变化时,界面波的频散特性随之变化.在此基础上进一步计算了不同界面粘接条件下法向线源脉冲激发的界...     

弱粘接结构中谐振频率与刚度比的数值研究

利用超声波垂直入射的方法,研究了粘接层界面具有弹簧模型的边界条件下,波的反射系数与谐振频率的关系。首先,利用粘接层界面的一次反射导出切向和法向刚度比表达式;其次,推导了粘接层界面存在多次反射和透射时刚度比、谐振频率及反射系数之间的关系,得到了弱粘接结构的反射系数随着不同刚度比的变化规律;最后,分析了弱粘接层厚度的变化对谐振频率的影响。理论分析和数值计算的结果表明:随着刚度比的增加,谐振频率向高频方向漂移;并且,随着粘接层厚度的增加,粘接结构将出现多阶谐振频率。     

多孔媒质界面上声波的反射和折射

一、引言 利用地震波进行石油勘探和利用超声波检测多孔材料时,了解声波在流体饱和的多孔媒质界面上的反射和透射特性十分重要。与一般的各向同性固体不同,多孔媒质中可以有传播速度不同的三种波型(快纵波、慢纵波和切变波)[1,2],其界面上声波的反射和折射行为较为复杂。Stoll[3]曾研究过流体中传播的平面纵波入射到水饱和的沉积岩表面上的反射系数,但未具体计算在多孔媒质中的折射波的振幅,也未考虑在多孔煤质中传播的声波入射到流体(或固体)界面时的反射和折射特性。Hovem[4]在研究声波通过浸没在流体中的多孔媒质栩透射特性时,为简便地…     

粘滞固体滑移界面层的超声测量

超声纵波与横波分别垂直入射到固体间的Stokes流体滑移界面层时,其反射系数与界面层的特性(包括粘滞系数、体积弹性模量、厚度)或入射波的频率有关.通过对纵横波两种波型各自在粘滞流体界面层的反射特性的讨论,结合两种粘滞性不同的流体界面层试验测量结果,说明了使用纵横波测量滑移界面层粘滞性的不同特点.     

阻尼材料粘接质量超声检测试验研究

为了研究阻尼材料粘接质量的超声检测方法,用超声透射法和反射法分别检测了一种阻尼材料的5种不同样品,结果表明:超声透射法和反射法能够检测出样品中模拟的夹杂气泡、粘接面开裂、异物夹入等粘接缺陷,对于带空腔结构的阻尼橡胶板,内部的空腔结构和粘接缺陷也都能检测出来。     

石墨高温粘接界面的组成及其与粘接强度间的关系

以酚醛树脂和碳化硼为原料制备了性能良好的调温粘结剂并对石墨材料进行粘接。通过XPS的测试，研究了石墨调温粘接样品在不同的温度热处理后的界面组成，相对含量变化及其与粘接性能间的相关性。结果表明，粘接界面上主要存在着C，B，O等元素，其中，酚醛树脂（PF）炭化产生的无定形炭构成了胶层骨架，其相对含量的变化影响着胶层结构的致密稳定性；B在粘接样品中以B4C或B2O3形式存在，其存在形式对粘接强度有着重要的影响。     

平面波与层状多孔介质海底的反射和透射

针对典型的海底介质结构情况,研究了从海水入射到含有非固结沉积层的层状流体饱和多孔介质海底的平面波的反射和透射问题,分析了沉积层和基岩中纵、横波速度和衰减的频散变化特点,在沉积层厚度和频率变化时,对海水-海底界面上的位移势函数反射系数进行了计算和分析。研究结果表明：在沉积层厚度一定的情况下,较高频率时,沉积层对海水中声场的影响较大,而频率较低时,基岩对海水中声场的影响较大。在以不同的掠射角入射时,由于沉积层中质点的法向共振,广义位移势函数反射系数随频厚积的变化曲线会出现一系列的共振峰,随着掠射角的减小,共振峰个数减少,但共振峰的幅度会增加。     

Anomalies in the ultrasound reflection from a solid-dissipative medium interface

The reflection of longitudinal acoustic waves from the interface between a solid and a strongly dissipative medium was theoretically studied. It is shown that the reflection coefficient and the reflected signal phase significantly depend on the coefficient of ultrasound absorption in the dissipative medium. An algorithm for restoring the time variation of the dissipative medium viscosity during solidification is proposed, which is based on the results of measurements of the amplitude reflection coefficient for a pulsed ultrasonic signal. The reflection and transmission coefficients are determined for the ultrasound wave amplitude, velocity, pressure, and intensity. An expression is derived for the acoustic energy absorbed upon reflection from a dissipative medium. A frequency dependence of the amplitude and generalized phase of the signals reflected from and transmitted through the interface are restored from the results of spectral calculations. The theoretical results are confirmed by experimental data on the reflection of acoustic pulses from an organic glass-epoxy compound resin interface measured during solidification of the latter medium. According to these data, the reflection coefficient and the reflected acoustic pulse duration decreased upon solidification of the epoxy compound.     

Wave scattering by a horizontal circular cylinder in a two-layer fluid with an ice-cover

In a two-layer fluid wherein the upper layer is of finite depth and bounded above by a thin but uniform layer of ice-cover modelled as a thin elastic sheet and the lower layer is infinitely deep below the interface, time-harmonic waves with a given frequency can propagate with two different wavenumbers. The wave of smaller wavenumber propagates along the ice-cover while wave of higher wavenumber propagates along the interface. In this paper problems of wave scattering by a horizontal circular cylinder submerged in either the lower or in the upper layer due to obliquely as well as normally incident wave trains of both the wave numbers are investigated by using the method of multipole expansions. The effect of the presence of ice-cover on the various reflection and transmission coefficients due to incident waves at the ice-cover and the interface is depicted graphically in a number of figures.     

声波在多层介质中传播的四端参数模型应用分析研究

声波在两种介质的交界面透射和反射时 ,借鉴机械四端参数法 ,利用声学边界条件 ,引入了四端参数矩阵 ,建立四端参数模型。通过对四端参数矩阵的分析 ,探讨了在简谐平面波垂直入射的条件下 ,声波在多层介质中的传播特性 ,并推导出声透射系数和声反射系数的一般计算公式。     

声波由粘弹性介质向流体介质入射情况下的声反射分析

在研究含腔体的结构的声学特性时,会遇到声波从粘弹性介质向流体介质入射的情况。主要研究了声波从粘弹性介质向流体介质斜入射情况下的声反射特性,分析表明：反射声波中有横波和纵波同时存在,纵波声压反射系数随入射角度的增大逐渐增大,横波的声压反射系数随入射角度的增加先增大后减小,在垂直入射时只有纵波,而没有横波存在。这些结论为进一步研究带空腔结构的声学特性打下了基础。     

Water wave scattering by a pair of thin vertical barriers with submerged gaps

The scattering of obliquely incident water waves by two thin vertical barriers with gaps at different depths has been studied assuming linear theory. Using Havelock’s expansion of water wave potential, the problem is reduced to two pairs of integral equations of the first kind, one pair involving a horizontal component of velocity across the gaps and the other pair involving the difference of potentials across each wall. These two pairs of integral equations can be solved approximately by employing a Galerkin single-term approximation technique to obtain numerical estimates for the reflection and transmission coefficients. These estimates for the reflection and transmission coefficients thus obtained are seen to satisfy the energy identity. The reflection coefficient is plotted against wave number in a number of figures for different values of various parameters involved in the problem. It is observed that the reflection coefficient vanishes at discrete frequencies when the vertical barriers are identical. For nonidentical vertical barriers the reflection coefficient never vanishes, though at some wave number it becomes close to zero. The results for a single barrier and fully submerged two barriers, and for a single barrier with a narrow gap, are also recovered as special cases.     

The applicability of plate wave techniques for the inspection of adhesive and diffusion bonded joints

The role of plate waves in the inspection of adhesive and diffusion bonded joints is examined. This involves a review of the modal techniques which have been proposed for the measurement of the adhesion and cohesion properties of adhesive joints and the presentation of some of our own studies on the detection and characterization of an unwanted layer of brittle alpha case in diffusion bonded titanium. It is concluded that Lamb waves, which occupy the whole joint, are viable in principle but are limited in both applications by their strong sensitivity to the material properties and the thicknesses of the adherends and their relative insensitivity to those of the bondline layer. On the other hand, embedded modes, which propagate along an embedded layer, are largely insensitive to the adherends, the dispersion curves showing a major improvement in sensitivity to the properties of the layer and to the boundary conditions between the layer and the adherends. The drawback is that their exploitation is limited in practice because it is difficult to excite and detect them. True modes offer good potential but require access to the ends of the joints. In attempting to excite leaky modes, minima of the reflection coefficient, commonly used to measure Lamb wave dispersion curves in immersion coupled plates, do not correspond to the dispersion curves because the acoustic impedance of the adherends is too large. Therefore, although measurement of the minima offers good potential for inspection, this is a response technique and cannot be associated directly with the plate modes. In neither of the examples studied could an interface wave exist at a single interface between the bondline layer and an adherend. However, in general such modes could be rather attractive for inspection, provided that their wavelengths are much smaller than the layer thickness, because they are sensitive to the interface region but not to the thicknesses of the layers, and they are relatively simple to measure.