Excitation and Detection of Nonlinear Waves on a Charged Surface of Liquid Hydrogen

A new technique for exciting nonlinear waves on a charged surface of liquid hydrogen is described. Methods of optical detection of surface oscillations in experiments on capillary turbulence at frequencies of up to 10 kHz are discussed. The results of a study of capillary waves on the surface of liquid hydrogen are presented.     

Propagation of Rayleigh Waves in an Elastic Wedge

Propagation of Rayleigh waves in an elastic wedge has been studied theoretically. The resulting curves for the refractive index are in good agreement with previously known experimental data.     

信号周期的一种数字化测量方法

介绍了精确评价周期信号序列的周期的一种方法,使用的手段是数字滤波与正弦波曲线拟合,并讨论了其拟合误差情况.以两组仿真实验结果,验证了本文所述方法及过程的正确性和实用性,从而实现了周期信号波形周期参数的精确评价.     

Energy Loss in the Impact of Elastic Spheres on a Rigid Half-Space in Presence of Adhesion

Adhesion can cause energy losses in asperities or particles coming into dynamic contact resulting in frictional dissipation, even if the deformation occurring is purely elastic. Such losses are of special significance in impact of nanoparticles and friction between surfaces under low contact pressure to hardness ratio. The objective of this work is to study the effect of adhesion during the normal impact of elastic spheres on a rigid half-space, with an emphasis on understanding the mechanism of energy loss. We use finite element method for modeling the impact phenomenon, with the adhesion due to van der Waals force and the short-range repulsion included as body forces distributed over the volume of the sphere. This approach, in contrast with commonly used surface force approximation, helps to model the interactions in a more precise way. We find that the energy loss in impact of elastic spheres is negligible unless there are adhesion-induced instabilities. Significant energy loss through elastic stress waves occurs due to jump-to-contact and jump-out-of-contact instabilities and can even result in capture of the elastic sphere on the half-space.     

板中Lamb波激励响应计算方法

采用基于半解析有限元的激励响应计算方法来求解薄板中Lamb波的激励响应结果,替代常规的实验方法,实现对薄板中Lamb波传播特性的仿真分析。与三维有限元仿真方法相比,采用激励响应计算方法仿真导波在波导介质中的传播过程可以节省计算量,提高效率。通过求解薄板中Lamb波的一般均质方程,基于频谱叠加原理,可以计算薄板中Lamb波激励响应结果。分别提取激励响应计算结果和实验测量数据,通过小波分析计算两种数据的Lamb波群速度。经验证,激励响应仿真计算结果与实验数据有很好的一致性,通过群速度频散曲线对比两种方法获取的数据,模态分析结论一致。激励响应计算方法还可以仿真计算任意截面波导介质中导波的传播过程,具有较好的通用性。     

Distribution of Elastic Displacements and Mechanical Stresses in a Laminated Transducer with Amplitude-Phase Excitation

Russian Journal of Nondestructive Testing - The paper considers how elastic displacements and mechanical stresses are distributed along a laminated transducer consisting of two piezoelectric plates...     

Circular Electromagnetic-Acoustic Converter of Surface Waves

The paper suggests a design of an electromagnetic-acoustic converter shaped as a ring and emitting and detecting circular surface waves. Several examples demonstrate that such converters can be used in nondestructive testing, namely, in detecting surface cracks and evaluating anisotropy of sheet materials.     

An Acoustooptical Microwave Deflector with the Surface Excitation of Ultrasound

An acoustooptical microwave deflector is described. Metal interdigital electrodes are used for the surface excitation of ultrasound in the acoustooptical guide of the deflector. At the modulated light wavelength of 0.63 m, the diffraction efficiency of the acoustooptical deflector within the working frequency range of 1500 to 2000 MHz is 5%/W; the frequency resolution is 1 MHz.     

Experimental Study of Diffraction of Elastic Waves on Crack Model

Russian Journal of Nondestructive Testing - Small-opening slots have been used to simulate cracks in butt welds. The influence of the orientation of the slot ribs on their detectability with pulse...     

Specific Features of Excitation and Propagation of Longitudinal and Transverse Subsurface Waves in Solids: I. Waves in Objects with a Free Plane Boundary

Specific features of excitation and propagation of transverse and longitudinal subsurface waves in solids are determined. Dependences of the parameters of the acoustic field generated in a solid body on the acoustic properties of a probe's wedge and of the tested body are found experimentally and compared to theoretical results. Using the amplitude and the directivity characteristic of the principal transverse mode and of accompanying secondary modes (longitudinal and Rayleigh), the optimum solutions for identifying subsurface flaws characterized by low reflectivity are determined. Studies of the passage of an acoustic signal through a magnetic-fluid acoustic guide and analysis of the magnetic-fluid's acoustic properties enable conclusions to be drawn regarding expediency of the usage of such media for excitation (detection) of longitudinal and transverse subsurface waves in materials with low velocity of sound (plastic, etc.)     

随机参数弹性连杆在平稳随机激励下的动力可靠性分析

研究随机参数弹性连杆机构在平稳随机激励下的动力响应分析。利用拓广的随机因子法,从求解系统固有频率的瑞利商公式出发,得出物理参数和几何参数均为随机变量的弹性连杆时变固有频率的均值和方差。从动力平稳随机响应在频域上的表达式出发,利用求解随机变量函数的矩法和数字特征的代数综合法,计算出随机参数弹性连杆机构在平稳随机激励下弹性位移和速度的均方值的均值、方差表达式,由动力可靠度的公式导出其动力可靠度的均值和方差的计算公式。通过算例,分析机构物理参数和几何尺寸的随机性对机构动力可靠度随机性的影响。     

基于非轴对称激励的管道裂纹时反导波检测研究

为解决目前管道导波时间反转检测方法需采用较多通道同步激励、接收的问题,在分析管中弯曲纵向模态簇导波激发特性的基础上,提出一种基于单一斜探头局部加载激励L(M,2)簇的时反检测方法。通过超声斜探头阵列和自行研制的时反激励/接收板卡验证该方法的可行性,并试验研究初始激励信号的类型、频率及时反窗宽等因素对管道裂纹时反检测效果的影响。结果表明,在不同检测频率,采用窄带和宽带信号进行初始激励,时反后相对时反前缺陷回波幅值均有较大提高,且回波信噪比也有较大改善,能明显区分出缺陷波包。     

基于压电激振的弹性模量测量方法

为了提高固体材料弹性模量测量精度以及简化测量过程,提出一种新的固体材料弹性模量测量方法。首先,采用压电陶瓷激振与拾振测试试件的一阶共振频率;其次,利用有限元仿真软件ANSYS对试件的振动模态进行仿真;最后,将实测的一阶共振频率与ANSYS仿真结果进行对比,从而推算出试件材料的弹性模量。分别对钛合金、铝合金、不锈钢试件的弹性模量进行了测量与分析,测量结果精确可靠。对钛合金相同批次、相同直径、不同长度的试件进行了测量,测量误差小于0.3%。该方法消除了传统动态共振测量法中数值拟合求一阶共振频率带来的误差,ANSYS模态仿真降低了对试件的形状要求,使测量过程简化,测量精度显著提高。     

Testing the Loading of Bearing Rings with Surface Waves Using Acoustoelasticity Effect

Russian Journal of Nondestructive Testing - The results of experimental studies of a nondestructive testing method for assessing the loading of bearing rings on an axle journal using the...     

Effectiveness of Electromagnetic-Acoustic Excitation of the Lamb Waves for Various Conducting Layer Thickness

The effectiveness of exciting the Lamb waves in realizing one of the possible variants of the electromagnetic-acoustic (EMA) conversion whose feature is the interaction between eddy currents induced in a plane layer and a nonuniform magnetic field generated by a direct current owing through the layer is considered. Simple relations between the EMA coupling coefficients are obtained in two limiting cases: when the thickness of the electrically conducting part of the layer is either much greater or much less than the skin-layer depth.     

Elastic Waves in an Inhomogeneous Austenite Plate in the Model of a Transversely Isotropic Medium

The effect of the elasticity modulus and density inhomogeneities on the elastic wave transmissivity through an austenitic steel plate has been investigated. The elastic properties of austenitic steel have been simulated by a transversely isotropic medium. The mutual action of the elastic anisotropy and spatial inhomogeneity has been considered. It has been shown that the main factors determining the interference pattern in the plate are the plate thickness, absolute value of the modulus (density) variation, and spatial derivative of the modulus. Properties of both inhomogeneous and homogeneous transversely isotropic plates have been compared with those of an isotropic plate. Studies of the elastic properties of austenitic steel using the model of transversely isotropic medium have been reviewed.     

点接触弹流润滑条件下表面弹性变形研究

为研究弹流润滑条件下点接触表面变形及其对表面性能的影响,采用激光微织构法制备了一组不同形貌参数的滚动轴承滚道表面试件,基于表面频谱分析和弹流润滑快速算法（幅值缩减法）分析了试件在不同工况参数下的弹性变形。使用ISO 25178三维形貌参数体系对变形前后表面进行表征,研究了点接触弹流润滑状态下表面形貌的弹性变形与载荷、转速的关系。研究结果表明,弹流接触使表面形貌发生显著的弹性变形,载荷、转速等工况参数对变形量影响较大,表面弹性变形使得形貌参数发生显著变化。     

弹性系统的激励和响应研究（8）

从部分多自由度线性无阻尼系统的振动响应函数的分解表达式中分析总结出多自由度系统的部分亲的振动响应特点,从部分特殊系统负载的各主要振动中响应幅值的近似结果中推出对应的振动中入特点。由此推出对某些特殊的多自由度系统的一些简化方法。     

弹性系统的激励和响应研究（6）

当多自由度无阻尼线性弹簧质量系统产生共振时,根据基础力平衡方程、求出系统的对应的共振响应函数。对比分析共振响应函数的组成与变化特点。     

Experimental Investigations into Laser Generation of Surface Acoustic Waves in Ferromagnetics

The effect of magnetic phase transition on the parameters of high-temperature conversion of pulse laser radiation into the acoustic field of surface waves (SAWs) was studied. For this purpose, an experimental setup was designed and assembled.