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。      

三层介质超声谐振模式随材料和界面粘接性能变化的演变规律

在用超声波谐振对粘接材料的粘接强度进行无损评估时, 不同模式对粘接强度的敏感程度受到众多因素和参数的影响, 对检测结果的可靠性至关重要. 基于多层介质中声传播和界面弱粘接边界条件的理论模型, 将一个上下非对称的金属-粘接剂-金属三层结构的平面波反射系数函数中的谐振模式看作是上下铝金属层各自的Lamb波频散模式通过夹心粘接剂层相互耦合后叠加组成. 改变影响结构粘接强度的因素, 即粘接剂的性能参数(声阻抗、密度、厚度)和界面切向劲度系数k_t来分析三层结构谐振模式耦合方式的变化,得出结论: 粘接结构粘接性能的变化基本上不改变与被粘铝层相关的固有部分的Lamb波模式, 而它们的耦合模式则在谐振频率上产生平移并会与固有模式进行交换和替代; 不同参数的变化引起的模式演变有各自的规律, 大多可彼此区分.     

背部支撑型空间反射镜镶嵌件粘接结构设计

基于不同的边界条件,建立了针对带锥度盲孔的空间相机反射镜组件胶层厚度的计算模型,利用力学模型计算粘接处符合设计要求的胶层厚度范围。通过建立的有限元模型,计算并拟合得到相应的胶层厚度-应力曲线,得出最优的胶层厚度为0.055mm。为了检验粘接结构的面形精度,进行了自重、温升条件下的反射镜组件镜面变化的模拟分析,采用温度载荷法模拟实际固化后胶层收缩对镜面的影响,并进行组件试验。仿真和试验结果表明,胶层厚度在0.055mm时反射镜组件具有足够的抵抗外界温变、振动干扰的能力,满足设计要求。     

单层与衬底胶接结构超声反射波谱的低频特征

理论研究了单层-衬底胶接结构超声反射波谱的低频(使用的超声波频率低于胶层的1/4波长共振频率)特征,指出了利用分层系统的谐振频率飘移量反演胶层厚度并进而评价胶层内聚强度的可能性。用Taylor展开给出了谐振频率所满足的非线性方程的显式解,其与Newton法数值解吻合得很好,适用范围远大于弹簧模型。在更低的频率范围,胶层可用熟知的线性弹簧模型描述。     

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。     

结构胶固化收缩对反射镜面形影响的分析与试验

在空间遥感领域,使用胶粘接技术安装光学元件越来越受到光机工程师们的青睐。与机械方法相比,胶粘接方法具有更轻的质量、更低的成本、更容易装配。大部分结构胶在固化期间存在收缩现象,结构胶的收缩会导致内应力出现,内应力又会导致光学表面发生变形,从而影响成像质量。为了在有限元分析中模拟这一过程,提出了等效线胀法的概念。该方法是将结构胶的线收缩率等效成胶的线胀系数,从而将结构胶固化过程的收缩等效成均匀温降导致的冷缩,以便进行热弹性分析。分析结果表明:在采用环带粘接方式时,粘接面积越小,镜面相应位置的面形误差越小,反之越大;粘接位置离镜面越远,镜面相应位置的面形误差越小,反之越大。对分析结果进行了试验验证,结果表明:当胶层质心到镜面距离为20.5mm、胶层宽度分别为15mm、20mm、25mm时,镜面PV值变化量分别为0.64λ、0.92λ、1.10λ;当胶层宽度为15mm、胶层质心到镜面距离分别为15.5mm、20.5mm、25.5mm时,镜面PV值变化量分别为1.08λ、0.64λ、0.40λ;当胶层质心到镜面距离为25.5mm、胶层宽度为25mm、胶层环形分布角分别为40°、60°、80°时,镜面PV值变化量分别为0.38λ、0.52λ、0.88λ。分析和试验结果为实际的工程应用提供了理论指导。     

粘接界面的非线性弹簧模型及实验验证

研究了纵波及横波垂直入射时在粘接界面处的非线性边界条件。在二阶微扰近似及粘接界面层厚度远小于入射声波长的条件下,给出了严格的界面非线性弹簧模型的表达式。数值计算结果表明,利用该模型得到的透射二次谐波与利用连续性边界条件得到的精确解吻合良好。针对钢(铝)的楔形粘接结构,在纵波垂直入射的条件下对该非线性弹簧模型进行了实验验证。实际测量结果显示该模型具有较高的精度;且被粘物与胶层的阻抗比越大,该模型的误差越小。     

固体滑移界面的超声评价

为评价固体滑移界面的特性,根据QSM界面模型和粘滞流体的本构方程导出了滑移界面的界面劲度系数及垂直入射到固体滑移界面的超声纵波和SH波的反射系数公式,其中纵波的反射系数与滑移界面层的绝热体积弹性模量、粘滞系数和入射声波的频率有关,而SH波的反射系数与界面层的绝热体积弹性模量和入射波的频率无关。因此,可以用SH波直接评价界面的不同粘滞状态,且不受检测频率的限制。要评价界面的绝热体积弹性模量,则必须增加纵波检测。利用蜂蜜和水模拟不同滑移界面层的声波反射实验验证了上述理论结果。     

BN&Al2O3/环氧树脂复合材料粘接层对LED灯结温的影响

自制BN/EP(环氧树脂)复合材料和Al₂O₃/EP复合材料作为LED灯PCB板和散热铝块之间的粘接层材料,采用精密钻孔的方法用高精度测温仪测量LED灯正常工作时的温度分布,讨论粘接层对结温的影响,并与COMSOL Multiphysics软件模拟结果进行对比分析。实验测量LED结温与模拟结温变化趋势基本一致,结温会随着粘接层厚度的增加而上升、随着粘接层复合材料热导率的增加先快速降低而后趋于平缓。最终得到PCB板和散热铝块间最佳粘接层厚度和粘接层复合材料配比,当BN的质量分数为60%时,BN/EP复合材料粘接层的热导率最高,此时LED结温为75.2 ℃,比纯环氧树脂粘接层LED的结温降低了27.6 ℃。而Al₂O₃/EP复合材料粘接层LED的最低结温为78.2 ℃,此时Al₂O₃的质量分数为50%。     

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。     

Modulated angle beam ultrasonic spectroscopy for evaluation of imperfect interfaces and adhesive bonds

An experimental method incorporating high frequency pulsed angle beam ultrasonic measurements modulated by low frequency vibrations of a bonded structure is described. This method uses parametric/nonlinear mixing between high and low frequencies to characterize adhesive degradation. It is demonstrated that good quality (undamaged) bonds exhibit little dependence of ultrasonic signature on the overlay of low frequency vibration loads; however, environmentally degraded or imperfect bonds exhibit strong modulation of the resonance frequency of the ultrasonic signal reflected from the bond. The results are interpreted using a model for normal and oblique wave interaction with two nonlinear interfaces separated by an adhesive layer under quasi-static stress modulation.     

Bonding Interface Imaging and Shear Strength Prediction by Ultrasound

The propagation of a longitudinal ultrasonic wave normally incident upon an adhesively bonded structure is studied. The structure consists of adherend and adhesive layers with finite thickness. Interfaces between adherend and adhesive are regarded as distributed springs. Theoretical and experimental results show that resonant frequencies of the bonded structure vary sensitively with the interface stiffness constants and adhesive thickness, and these interface characteristics are inversed by the simulation annealing (SA) method. Furthermore, the distribution image of interface stiffnesses is compared with the state of fracture interface, and quantitative prediction of shear strength is achieved based on the distribution of interface stiffnesses and adhesive thicknesses by using a back-propagation neutral network. The average relative error of the shear strength from prediction to real value is 10.7%.     

GMM/弹性板/PZT层状复合结构的纵振磁电响应

利用Hamilton原理推导GMM/弹性板/PZT三层层状复合结构的运动方程，在推导中考虑层间胶层的作用，包括其剪切变形和纵向变形产生的效果；应用运动方程，根据层状复合结构的边界条件，推导复合结构的固有频率方程，并结合压磁和压电方程，得到层状复合结构在不同固有频率处的磁电响应.对比磁电响应的频率特性的理论值和实验值，频率误差在9.42%以内，磁电电压转化系数的理论值与实验值符合，并讨论了弹性板的尺寸变化对层状复合结构谐振频率的影响. 关键词： 层状复合结构 磁电响应 Hamilton原理 运动方程     

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。     

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.     

Laser ultrasonic characterization of adhesive bonds between epoxy coating and aluminum substrate

Nanosecond pulsed laser irradiation through transparent epoxy bonded to aluminum substrate excites wide-band ultrasonic waves at the bonded interface. The normal displacements on the rear surface of aluminum produced by the direct and multi-reflected longitudinal waves in the coating layer are detected by a laser interferometer. The amplitude of the reflected signal depends on the properties of the coating/substrate interface, which is described by terms of the interfacial stiffness using a spring boundary model. The waveforms at the epicenter versus interfacial stiffness are simulated and found to be in good agreement with experimental results. The relation between the interfacial stiffness and the amplitude ratio of the reflected and direct waves is thus established. An image of amplitude ratio of a specimen (null 10 mm) is obtained from the epicenter waveforms recorded by a laser ultrasonic scanning system, which shows the distribution of bond quality on the bonding interface.     

How acoustic cavitation can improve adhesion

In general, ultrasound is commonly used at low power level for non-destructive testing (NDT) and detection of delaminations in adhesive bonded structures. The present paper instead presents an approach where power ultrasound is used to improve interface formation prior to the bonding process and to ensure the quality of adhesive bonds by using acoustic cavitation in the liquid adhesive.Results from high-speed videos, rheological and thermal measurements and destructive testing of adhesive bonds with contaminated surfaces are presented and discussed. Power ultrasound can be used in general to improve adhesion and significantly to improve contamination tolerance and robustness of adhesive bonding processes.     

Air-coupled ultrasonic testing of diffusion bonds

The diffusion bond between two steel plates can be ultrasonically evaluated, at normal incidence in an immersion experiment, by analyzing the frequency dependence of the echo reflected from the imperfect bond. The interfacial stiffness, derived from the echo amplitude, correlates well with the bond-strength. However, a non-contact method is desirable for applications where immersion or contact is not wanted or even dangerous for damaging the material. This above mentioned bond-echo technique would not work in the situation of air-coupling as the reflected echo becomes then too weak due to the high impedance mismatch at the air-solid interface. Therefore we propose a theoretical method based on the study of two neighbouring resonance frequencies of the diffusion bonded plate-plate structure. In this way the physical signal sensitive to the adhesion status is not the (too weak) echo reflected from the bond, but the resonance frequency of the whole plate-plate system, and this frequency is detectable as working at resonance ensures high enough signal levels. It was shown that the odd resonance is as well sensitive to the plate thickness as to the interfacial bond parameter, whereas the even resonance feels only the plate thickness. On the basis of a theoretical formula, it is possible to extract, from a single point measurement, out of these two resonance frequencies both the plate thickness and the interfacial stiffness. In this way bond information is separated from geometrical information. Finally it is shown that thickness differences between the plates did not affect the reliability of the bonding-strength predictions.