岩石等非线性介观弹性固体材料的谐波特性的超声研究

岩石、混凝土等非线性介观弹性固体材料显示出与经典的非线性声学不同的非经典非线性声学现象,比如滞后现象、离散记忆等.本文实验研究了超声波在岩石材料中产生的基波、二次、三次谐波随声源幅度的依赖关系,研究了岩石的超声衰减,与金属材料的进行了对比;并且将浸水后的混凝土与浸水前的混凝土的超声谐波特性进行了对比,对此实验现象作出了定性的解释.此研究有利于岩石等非线性介观弹性固体材料的无损检测的研究.     

声波在锥棒中非经典非线性传播及实验验证

弹性体材料在早期退化阶段会出现一些长度不同,且分布不均匀的介观尺度微裂纹,声波在这些裂纹聚集区(或裂纹群)传播会激发较强的非经典非线性。文中以缓变截面的锥棒为研究对象,在Preisach-Mayergoyz (PM)空间模型下研究了声波通过微裂纹聚集区激发的非经典非线性谐波传播特性,实验验证了三次谐波位移幅度与缺陷位置、宽度的反演关系。理论计算和实验结果表明:微裂纹群激发了较强的奇次谐波,引起非经典非线性传播;其谐波幅度与微裂纹聚集区域位置、宽度及非经典非线性参数紧密相关,利用三次或五次谐波位移幅度能够准确定位缺陷的区域。      

测量三阶弹性常数的非线性声学方法

三阶弹性常数反映了固体弹性在二级近似下的非线性性质，它在固体物理和材料特性的确认和评估中起着重要作用。着重介绍了测量三阶弹性常数的超声二次谐波激发方法。     

声波在有裂纹的固体中的非经典非线性传播

固体材料的无损检测是一个非常重要的课题,带裂纹的固体材料显示非经典非线性声学现象,本文对此现象进行了实验和理论研究.从实验上一维观察到此现象,发现奇次谐波振幅与基波振幅呈平方关系,与理论预计基本吻合;理论上从二维的角度数值模拟了声波在有损耗的带裂纹的固体中的声传播,并讨论了经典非线性和非经典非线性对声传播的影响,发现裂纹的贡献主要体现在非经典非线性上.分析了样品中裂纹的宽度和位置与非线性声参数的关系,在靠近样品中心的两个对称区域以及距离声源较近点,非线性声参数对样品的破损较为敏感,而在中央和距声源最远端敏感性较低;随着裂纹宽度的扩大,非线性声参数也开始变大,但在破损区域蔓延到棒边缘之前,有下降的趋势.     

固体粗糙界面与超声的非线性相互作用研究

本文提出了一种随机弹性接触界面与超声的非线性相互作用理论. 首先建立了描述随机弹性接触界面的模型, 然后分别研究了界面间应力-应变关系在线性简化模型、指数模型、高斯模型下与超声的非线性相互作用. 数值仿真和实验研究结果均表明高斯模型更适合描述固体接触界面. 本文在介观结构上解释了固体界面与超声的相互作用, 对工业超声无损检测裂缝、缺陷及损伤有指导意义. 关键词： 超声无损检测 固体粗糙界面 非线性效应     

高功率超声脉冲激励下金属板的非线性振动现象研究

对高功率超声脉冲作用下金属板中的超谐波、次谐波、准次谐波以及混沌等非线性振动现象进行了实验和理论研究.在实验中,高功率超声换能器产生脉冲调制的高频振动激励金属板产生非线性振动,利用激光测振技术测量不同尺寸和不同固定方式下金属板复杂的非线性振动情况,并对其进行了时序分析、频谱分析以及相空间分析.根据实验条件,提出包含非线性接触阻尼的振动-碰撞动力学模型,用以研究强超声振动-碰撞作用下的板非线性振动机制,并进行了相应的理论计算.计算结果表明,超声换能器的变幅杆与金属板之间的间歇性高频碰撞作用是金属板强非线性振 关键词： 非线性板振动 强超声脉冲激发 振动-碰撞动力学     

包膜超声造影微泡次谐波特性的优化设计与实验研究

基于包膜超声造影微泡在超声场中的理论振动模型,对其次谐波特性进行优化设计,从理论上计算和分析了微泡粒径、膜弹性及声压等对微泡次谐波响应的影响,以期获得其用于非破坏性次谐波成像的最佳条件。另外通过改变膜材料的配比, 制备了具有不同膜弹性的超声造影微泡,对其声学特性进行了体外声学实验测定。仿真计算和实验结果表明,在合适的膜材料配比条件下,制得的平均粒径为3μm左右的包膜微泡,可获得满意的次谐波响应,并且其用于非破坏性次谐波成像时的最佳工作声压约200-400 kPa。     

固体性能研究中的非线性超声波

有限振幅的超声波在固体中传播时会发生波形畸变,伴随着高次谐波的出现。波形畸变主要来自两个方面:固体中晶格原子之间作用力的非线性以及固体中位错和超声的非线性相互作用。本文评述了这些机制所引起的超声非线性传播特征,高次谐波振幅与固体三阶弹性常数的关系以及超声非线性谐波的测量在固体疲劳效应、微裂缝检测中可能的应用。本文也简述了测量超声非线性畸变的实验方法,指出了超声非线性传播中某些有兴趣的问题。     

固体性能研究中的非线性超声波

有限振幅的超声波在固体中传播时会发生波形畸变,伴随着高次谐波的出现。波形畸变主要来自两个方面:固体中晶格原子之间作用力的非线性以及固体中位错和超声的非线性相互作用。本文评述了这些机制所引起的超声非线性传播特征,高次谐波振幅与固体三阶弹性常数的关系以及超声非线性谐波的测量在固体疲劳效应、微裂缝检测中可能的应用。本文也简述了测量超声非线性畸变的实验方法,指出了超声非线性传播中某些有兴趣的问题。     

颗粒固体弹性势能的声波性质

基于大量静止颗粒堆积而成的物体属于非线性弹性体的观点,计算了其弹性势能的声速表达式(考虑圆柱对称和沿主应力方向传播的平面波情形).通过与己报道的一些实验数据的对比,认为精密的声学方法能够测定势能中的所有材料参数,因此是研究这类材料非线性弹性行为细节的一个重要观测手段,但需要对样品的所有应力、密度和均匀程度进行全面仔细的监控.     

高温超导薄膜微波非线性器件设计初探

本文讨论高温超导薄膜微波非线性器件的若干问题,包括材料建模,元件建模,器件参数建模,最后通过这些参数完成高温超导薄膜微波非线性器件综合等.试图通过非线性测试提取高温超导薄膜微波材料非线性模型,根据材料非线性模型建立非线性传输线模型,由非线性传输线模型建立各种微波无源元件模型,最后实现非线微波器件综合设计.     

有机聚合物的非线性光学

有机聚合物是一类非常重要的非线性光学材料,这是因为它在光通信和高密度光存储等高技术领域中有良好的应用前景。有机聚合物的非线性光学性质是过去２０年来理论和实验的重要研究课题。文章在简要介绍非线性光学之后,着重论述了有机聚合物光学非线性的来源和这些材料中二阶、三阶非线性光学效应及非线性光吸收的特点。最后,简要介绍了作者在有机聚合物非线性光学研究中几个近期结果,如“全光极化、三阶光学非线性的激发态增强、     

Local interaction simulation approach to modelling nonclassical,nonlinear elastic behavior in solids

Recent studies show that a broad category of materials share "nonclassical" nonlinear elastic behavior much different from "classical" (Landau-type) nonlinearity. Manifestations of "nonclassical" nonlinearity include stress-strain hysteresis and discrete memory in quasistatic experiments, and specific dependencies of the harmonic amplitudes with respect to the drive amplitude in dynamic wave experiments, which are remarkably different from those predicted by the classical theory. These materials have in common soft "bond" elements, where the elastic nonlinearity originates, contained in hard matter (e.g., a rock sample). The bond system normally comprises a small fraction of the total material volume, and can be localized (e.g., a crack in a solid) or distributed, as in a rock. In this paper a model is presented in which the soft elements are treated as hysteretic or reversible elastic units connected in a one-dimensional lattice to elastic elements (grains), which make up the hard matrix. Calculations are performed in the framework of the local interaction simulation approach (LISA). Experimental observations are well predicted by the model, which is now ready both for basic investigations about the physical origins of nonlinear elasticity and for applications to material damage diagnostics.     

Conditioning-induced elastic nonlinearity in hysteretic media

The definition and measurement of the nonlinear elastic properties of a sample is of great importance for a large number of applications, including characterization of material performances and damage detection. However, such measurements are often influenced by spurious effects due to a combination of nonlinearity and nonequilibrium phenomena. We will present experimental data to show how nonlinearity due to small cracks in concrete samples increases as a consequence of conditioning, i.e., after having perturbed them with a constant amplitude excitation. In addition, our experimental data highlight “memory effects,” i.e., they show that when the excitation is removed, the elastic modulus does not return instantaneously to the initial value.     

Study of critical behavior in concrete during curing by application of dynamic linear and nonlinear means

The monitoring of both linear and nonlinear elastic properties of a high performance concrete during curing is presented by application of compressional and shear waves. To follow the linear elastic behavior, both compressional and shear waves are used in wide band pulse echo mode. Through the value of the complex reflection coefficient between the cell material (Lucite) and the concrete within the cell, the elastic moduli are calculated. Simultaneously, the transmission of a continuous compressional sine wave at progressively increasing drive levels permits us to calculate the nonlinear properties by extracting the harmonics amplitudes of the signal. Information regarding the chemical evolution of the concrete based upon the reaction of hydration of cement is obtained by monitoring the temperature inside the sample. These different types of measurements are linked together to interpret the critical behavior.     

Some Nonlinear Rock Behavior Effects

The nonlinear rock behavior effects observed in loading diagrams are analyzed which are usually ignored in conventional models of elastoplastic media. The initial deformation stage and unloading of rock samples are considered. The nonlinear behavior on these loading stages is interpreted from the viewpoint of partial closure of cracks initiated during deformation beyond the elastic limit or in earlier loading history. Phenomenological relations are derived to account for the discussed nonlinear effects in numerical modeling. The postcritical deformation stage corresponding to the stage of strain localization and main crack formation is studied. Corrections are made to provide a more accurate determination of model parameters.     

基于幅度调制的非线性超声相控阵成像方法*

超声相控阵是超声检测领域常用的材料缺陷定位和成像技术,可便捷快速地对裂纹、孔洞等缺陷进行成像。但是,传统超声相控阵方法对较小缺陷如闭合裂纹不太敏感。非线性超声信号因对材料性能退化以及微小缺陷敏感而广受关注。本文针对疲劳闭合裂纹检测,提出一种基于幅度调制的非线性超声相控阵成像方法,通过测量物理聚焦和虚拟聚焦两种聚焦模式下超声扩散场中的声能差,并将其作为非线性参量,实现疲劳裂纹闭合部分的定位成像和定量表征。将该法应用于7075铝合金试样疲劳裂纹的实验测量,并研究了扩散场信号延迟时间对非线性超声相控阵成像结果的影响。结果表明：相较于传统超声相控阵全聚焦法,基于幅度调制的非线性超声相控阵成像方法能够更准确地定位和成像疲劳裂纹闭合部分;延迟时间的选择对疲劳裂纹长度的表征精度影响较大,本文研究了该延迟时间的选择方法并实现了检测结果的优化。     

Experimental analysis of the linear and nonlinear behaviour of composites with delaminations

An analysis of the linear and nonlinear vibration responses of composites with delaminations is presented. The effect of delamination size on the linear and nonlinear vibration response is studied. The composite material used in this paper is a glass fibre reinforced plastic (GFRP) having delaminations at the plies interfaces. The experimental procedure consists in inducing the specimen on its resonance flexural modes with different excitation levels (amplitudes) for six bending modes and for each delamination length. The presence of the nonlinearity introduced by the delamination was clearly identified by the variation of natural frequencies for increasing excitation levels. Then, nonlinear elastic parameters for progressive delamination length were determined and discussed for the first six bending modes. The linear and the nonlinear elastic parameters were compared in their sensitive modes.     

相对转动非线性动力学方程的稳定性及在一类非线性弹性系数下的解

建立一类含非线性弹性力的二端面转轴相对转动非线性动力学方程.对相对转动非线性自治方程进行定性分析，研究方程的稳定性.用参数变换法求得相对转动非线性非自治方程在强迫激励下的高次近似解.     

Concrete damage diagnosed by using non-classical nonlinear acoustic method

<正>It is known that the strength of concrete is seriously affected by damage and cracking.In this paper,six concrete samples under different damage levels are studied.The experimental results show a linear dependence of the resonance frequency shift on strain amplitude at the fundamental frequency,and approximate quadratic dependence of the amplitudes of the second and third harmonics on strain amplitude at the fundamental frequency as well.In addition,the amplitude of the third harmonics is shown to increase with the increase of damage level,which is even higher than that of the second harmonics in samples with higher damage levels.These are three properties of non-classical nonlinear acoustics.The nonlinear parameters increase from 10~6 to 10~8 with damage level,and are more sensitive to the damage level of the concrete than the linear parameters obtained by using traditional acoustics methods.So,this method based on non-classical nonlinear acoustics may provide a better means of non-destructive testing(NDT) of concrete and other porous materials.