钢-铅粘接结构的粘接强度对超声体波反射与 透射特性的影响*

针对多层异种金属粘接结构中粘接强度的超声检测与表征困难的问题,采用线性弹簧模型和等效弹性模量模型来分别表征界面粘附强度和内聚强度,推导了超声体波斜入射N层粘接结构的反射与透射系数表达式。通过在不同入射面和入射声波模式等条件下,同时连续改变两种参数来系统研究粘接层界面粘附强度与内聚强度变化对超声波反射与透射特性的影响关系,确定了能够敏感表征粘接强度的超声参量,为粘接强度的无损检测与评价提供理论依据。     

复合结构界面粘接强度的声-超声评价研究

基于Ritec-SNAP测量系统建立了声-超声技术实验系统,分析了在声-超声技术评价过程中用声信号的幅频特性及应力波因子表征复合结构界面粘接强度的可行性。用粘接层的固化过程模拟复合粘接板粘接强度的变化过程,以粘接层的固化时间作为粘接强度的间接表征参量,借助于已建立的实验系统对复合结构粘接强度的评价问题进行了实验研究。实验结果表明,应力波因子与反映界面粘接强度的粘接层固化时间呈单调对应关系,且不同固化时期的应力波因子存在明显的不同特性,表明用应力波因子评价复合结构的界面粘接强度具有可行性。     

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。     

粘接界面特性的超声检测与评价

粘接界面特性的超声检测与评价既是物理学的前沿问题,又是经济建设和国防安全亟需解决的应用问题。高波阻介质下多层低波阻介质界面脱粘检测、滑移界面检测和粘接强度定量评价是粘接质量检测中遇到的三大难题。本文综述了课题组十余年来在攻坚三大难题方面的研究工作：建立了共振匹配理论,发明了六项关键技术并实现了技术集成,研制出全新概念的超声检测设备,解决了第一个难题;成功研制出横波直探头,用纵横波综合判断方法解决了第二个难题;对第三个难题,建立了粘接界面非线性弹簧模型,为利用非线性声学参量评价粘接界面奠定了理论基础,并探索性地利用统计性方法对粘接强度进行了预测,取得较好效果。     

等厚铝板粘接件超声反射频谱的低频特征

利用弹簧模型研究了"铝-胶-铝"等厚粘接件的超声反射谱的低频特征(使用的超声波频率远低于胶层的共振频率),指出了利用其谐振频率的"右峰"漂移量反演弱粘接情况的胶层劲度系数的可能性。我们通过胶层固化时间的变化来模拟胶层劲度系数的变化,对理论结果进行验证,实验结果与理论吻合良好。     

钛合金和碳纤维的粘接技术

简述了某空间遥感相机中碳纤维桁架杆与钛合金接头的粘接工艺,通过对粘接剂的选择、粘接表面处理、胶层厚度等粘接强度影响的分析和破坏性力学试验表明,J133胶粘剂适用于钛合金和碳纤维材料的粘接;适当提高粘接表面的粗糙度、用化学法对粘接表面进行处理均可提高粘接强度;对该例的套接形式胶层厚度控制在0.15mm—0.2mm可保证得到好的力学性能和粘接质量。     

双层粘接板界面的超声非线性谐振特性分析

采用声-力-电类比建立粘接界面非线性力学行为的等效非线性振荡电路,以求解双层粘接板的超声非线性谐振频率。理论上导出非线性谐振频率方程,确定双层粘接板非线性谐振频率与激励幅度、三阶弹性劲度系数的解析关系。双层粘接铝板的超声实验发现:在不良粘接情形下,超声谐振频率发生偏移,其值大于粘接完好区,且激发了较强的三次谐波,但二次谐波幅度变化不大。实验结果表明三次谐波幅度上升,超声谐振频率也显著增大,与理论导出非线性谐振频率变化规律相吻合,且三次谐波与基波、二次谐波的比值反映了非线性谐振频率变化趋势,证实粘接层三阶劲度系数是产生非线性共振频率偏移的主要因素。      

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。     

厚胶层复合材料弱粘接结构的超声反射特性

开展了复合材料粘接结构粘接质量的非接触式超声反射特性的仿真与实验研究。首先,建立了水浸环境下纤维增强复合材料(FRP)单层板时域仿真模型,数值分析了不同入射角度下声反射系数频率谱的变化规律,并与已有理论方法进行了对比验证。基于此,建立了含厚胶层的复合材料粘接结构反射特性时域仿真模型,分析了粘接界面弱化程度对超声反射系数频谱特征点的影响规律。基于水浸超声反射特性测量系统,实验萃取了完好粘接状态的FRP粘接结构的超声反射系数频谱,与仿真结果吻合良好。随后,制备了具有不同粘接界面状态特征的FRP粘接结构试样,从实验角度揭示了单/双粘接界面弱化状态与超声反射特性间规律性的偏移特征。基于不同粘接状态与超声反射特性间的规律性分布特征,可为厚胶层复合材料粘接结构的粘接质量评估提供新的研究思路。     

用阴影法观察水声模型的声场

我们建立了一套用于显示模拟海底反射声场的光学系统。实验水声模型是由水-玻璃粉-玻璃-铝组成的三层模拟海底结构,声源是一个管状换能器,其轴线平行于分界面。实验用这套系统记录了从水下三个界面反射的六组波的声场图像。并且分辨出了它们各自的传播路径。从声场图像也可以得出水-玻璃粉界面、玻璃粉-玻璃界面的面波声速,玻璃粉和玻璃中的体波声速以及它们的厚度,结果与预先测出的参数符合。     

套管中模式波的响应特征*

在固井质量评价中主要利用套管中模式波的幅度或衰减变化反映水泥的胶结状况,不同测井仪器在套管中激发的模式波的类型不同,研究套管中各模式波的传播特征和影响因素可充分挖掘测量数据的潜在应用价值。CBL和SBT等测井仪器在套管中主要激发拉伸波,类同于平板中的零阶对称Lamb波,水泥环封隔测井仪器的斜入射模式在套管中主要激发套管弯曲波,类同于平板中的零阶反对称Lamb波,垂直入射模式激发套管共振波,类同于平板中的高阶对称Lamb波。该文重点分析了这些模式波的衰减特征及其对微环的响应,套管弯曲波在套后耦合轻质水泥时对微环不敏感,但在套后耦合常规水泥或重水泥时,其衰减明显高于胶结良好的状况;拉伸波对微环的存在最为敏感;套管共振波对微环不敏感。     

SH ultrasonic guided waves for the evaluation of interfacial adhesion

Shear-Horizontally (SH) polarized, ultrasonic, guided wave modes are considered in order to infer changes in the adhesive properties at several interfaces located within an adhesive bond joining two metallic plates. Specific aluminium lap-joint samples were produced, with different adhesive properties at up to four interfaces when a glass–epoxy film is inserted into the adhesive bond. EMAT transducers were used to generate and detect the fundamental SH₀ mode. This is launched from one plate and detected at the other plate, past the lap joint. Signals are picked up for different propagation paths along each sample, in order to check measurement reproducibility as well as the uniformity of the adhesively bonded zones. Signals measured for four samples are then compared, showing very good sensitivity of the SH₀ mode to changes in the interfacial adhesive properties. In addition, a Finite Element-based model is used to simulate the experimental measurements. The model includes adhesive viscoelasticity, as well as spatial distributions of shear springs (with shear stiffness K_T) at both metal–adhesive interfaces, and also at the adhesive–film interfaces when these are present. This model is solved in the frequency domain, but temporal excitation and inverse FFT procedure are implemented in order to simulate the measured time traces. Values of the interfacial adhesive parameters, K_T, are determined by an optimization process so that best fit is obtained between both sets of measured and numerically predicted waveforms. Such agreement was also possible by adjusting the shear modulus of the adhesive component. This work suggests a promising use of SH-like guided modes for quantifying shear properties at adhesive interfaces, and shows that such waves can be used for inferring adhesive and cohesive properties of bonds separately. Finally, the paper considers improvements that could be made to the process, and its potential for testing the interfacial adhesion of adhesively bonded composite components.     

Acoustic resonance scattering from a multilayered cylindrical shell with imperfect bonding

The method of wave function expansion is adopted to study the three dimensional scattering of a time-harmonic plane progressive sound field obliquely incident upon a multi-layered hollow cylinder with interlaminar bonding imperfection. For the generality of solution, each layer is assumed to be cylindrically orthotropic. An approximate laminate model in the context of the modal state equations with variable coefficients along with the classical T-matrix solution technique is set up for each layer to solve for the unknown modal scattering and transmission coefficients. A linear spring model is used to describe the interlaminar adhesive bonding whose effects are incorporated into the global transfer matrix by introduction of proper interfacial transfer matrices. Following the classic acoustic resonance scattering theory (RST), the scattered field and response to surface waves are determined by constructing the partial waves and obtaining the non-resonance (backgrounds) and resonance components. The solution is first used to investigate the effect of interlayer imperfection of an air-filled and water submerged bilaminate aluminium cylindrical shell on the resonances associated with various modes of wave propagation (i.e., symmetric/asymmetric Lamb waves, fluid-borne A-type waves, Rayleigh and Whispering Gallery waves) appearing in the backscattered spectrum, according to their polarization and state of stress. An illustrative numerical example is also given for a multi-layered (five-layered) cylindrical shell for which the stiffness of the adhesive interlayers is artificially varied. The sensitivity of resonance frequencies associated with higher mode numbers to the stiffness coefficients is demonstrated to be a good measure of the bonding strength. Limiting cases are considered and fair agreements with solutions available in the literature are established.     

Three-Dimensional Scattering of an Incident Plane Shear Horizontal Guided Wave by a Partly through-Thickness Hole in a Plate

We investigate the three-dimensional(3D) scattering problem of an incident plane shear horizontal wave by a partly through-thickness hole in an isotropic plate,in which the Lamb wave modes are also included due to the mode conversions by the scattering obstacle in the 3D problem.An analytical model is presented such that the wave fields are expanded in all of propagating and evanescent SH modes and Lamb modes,and the scattered far-fields of three fundamental guided wave modes are analyzed numerically for different sizes of the holes and frequencies.The numerical results are verified by comparing with those obtained by using the approximate Poisson/Mindlin plate model for small hole radius and low frequency.It is also found that the scattering patterns are different from those of the SO wave incidence.Our work is useful for quantitative evaluation of the plate-like structure by ultrasonic guided waves.     

Effect of the surface free energy on the behaviour of surface and guided waves

The aim of this paper is to evaluate the influence of the surface free energy upon the propagation of the eigenmodes of structures, by studying successively (a) the Rayleigh wave for an elastic half-space, (b) the Lamb waves for an elastic layer, and (c) the guided modes for a tri-layer structure (e.g., metal/adhesive/metal). The surface free energy is a parameter which appears in the jump conditions of stresses and displacements at each interface, and which consequently modifies the eigenmodes, solutions of the boundary conditions system. As expected, the Rayleigh wave is dispersive and its velocity increases when the surface free energy increases. In the same way, the velocity of Lamb waves also increases except at normal angle of propagation where the surface free energy does not arise. Moreover, near the Rayleigh angle, the behaviour of the A₀ and S₀ Lamb modes varies strongly according to the surface free energy. Similar results are observed for the tri-layer structure.     

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.     

Scattering of Lamb waves by a circular cylinder.

Following our previous attempt at the scattering from a cylinder in a slab to the incidence of a guided shear wave, we hereby discuss the scattering by an elastic cylinder embedded in an isotropic plate for a variety of bonding states to incidence of the fundamental Lamb wave modes S0 and A0 at the low-frequency regime. The plate is divided up into three regions by introducing two imaginary planes located symmetrically some distance from the cylinder and perpendicular to surfaces of the plate. The wave fields in various regions are expanded either into cylinder wave modes or into Lamb wave modes. A system of equations determining the coefficients of expansion is obtained according to the traction-free boundary conditions on the plate walls and the displacement and stress continuity conditions across the virtual planes. By taking an appropriate finite number of terms of the infinite expansion series and some selected points on the two properly chosen imaginary planes and the surfaces of the plate through convergence and precision tests, a matrix equation to numerically evaluate the expansion coefficients is found. Coefficients of the reflection and transmission versus the normalized radius of the cylinder in welded, slip, and cracked interfacial conditions are numerically computed. In the low-frequency range, the relative errors are found to be less than 1%. Contrast curves of the reflection coefficient for the cylinder of nearly all permissible size in perfect and imperfect interfacial bonding are shown and prominent differences are noted.     

Calculation of leaky Lamb waves with a semi-analytical finite element method

A semi-analytical finite element method (SAFE) has been widely used for calculating dispersion curves and mode shapes of guided waves as well as transient waves in a bar like structures. Although guided wave inspection is often conducted for water-loaded plates and pipes, most of the SAFE techniques have not been extended to a plate with leaky media. This study describes leaky Lamb wave calculation with the SAFE. We formulated a new solution using a feature that a single Lamb wave mode generates a harmonic plane wave in leaky media. Dispersion curves obtained with the SAFE agreed well with the previous theoretical studies, which represents that the SAFE calculation was conducted with sufficient accuracy. Moreover, we discussed dispersion curves, attenuation curves, and displacement distributions for total transmission modes and leaky plate modes in a single side and both two side water-loaded plate.     

Guided waves in a stratified half-space

The dispersion and excitation mechanisms and the energy distribution of guided waves in a stratified half-space are studied. All possible guided waves excited by a symmetric point source in two or three-layer medium models and their relation to the medium parameters are analyzed in detail. The excitation and propagation characteristics, as well as the energy distribution along the depth direction, of all modes of the surface waves and trapped waves are numerically investigated and analyzed thoroughly not only in the case when the shear wave velocity increases from up to down layers but also when a low-velocity layer is contained in halfspace, especially when the shear wave velocity decreases from up to down layers. It is found that there exist many guided wave modes in the case where the shear wave velocity of each layer increases from up to down layers. However, there is less than one guided wave mode in the case where the shear wave velocity of each layer decreases from up to down layers. The trapped waves exist and propagate along the low-velocity structure in the stratified half-space. It is also found that the characteristic of a mode is related to the source frequency. It is possible that a surface wave at one value of frequency is like a trapped wave at another value of frequency. Finally, the relation of the characteristics of all guided waves (surface waves and trapped waves) to the parameters of media is studied.