Diagnostics of Multilayered Composite Structures with the Help of a Fiber-Optic System for Strain Measurements

The paper considers a built-in fiber-optic array system for technical diagnostic of composite structures measuring local strains in hazardous cross sections of these structures. The effect of repeated microscopic bends of optical fibers on the transmitted flux in structures strained by a tensile force of up to 1 kN over a temperature range of 20 to 100°C has been investigated. The increase in the tensile stress in components of a composite structure leads to a growth in the optical losses of up to 20–23% of the initial optical flux. The loss function (F) is linear in the region of mechanical forces of up to 1 kN and temperatures up to 40°C. An explanation has been suggested for the nonlinearity of (F) at temperatures above 40°C. The conclusion is that the developed system enables one to estimate the strength of multilayered composite structures and detect their prefracture states using singular points on opto-mechanical characteristics of optical fibers.     

Application of acoustic microscopy to the measurement of some physical parameters of ceramics

The scanning acoustic microscope is a valuable tool for the ultrasonic non-destructive testing of ceramic materials or sintered metals, like titanium compounds. Bulk defects, responsible for the mechanical aging and breakdown of parts, are easily detected and imaged. Moreover, diffuse structures are evidenced in these images, forming a continuous background. In this paper, we present a method which enables the determination of physical parameters, like the density and the bulk grain size of the materials, from this background. This information is extracted, using a statistical approach, from the histograms pertaining to materials with a spectrum of different microstructures, based on a principal component analysis (PCA). It may be noted that the size of the microstructure elements accessible by this method can be lower than the spatial resolution of the microscope.     

超声波马达的真空和温度特性研究

研究了超声波马达在非常状态下的驱动行为,选取了5种工程塑料作为转子摩擦材料,利用真空试验机和自制的与其相匹配的超声波马达模拟试验台,采用对比试验方法,研究了接触预紧力、真空度和环境温度等对行波型超声波马达的驱动特性的影响。结果表明,随着预紧力和真空度的增加,马达的堵转力矩增加而空载转速下降;随着环境温度的增加马达的空载转速下降。运用声学理论分析了真空度对接触状态的影响,得出声悬浮作用使定子和转子的动态接触力减小的结论。在真空状态下,超声波马达的堵转力矩比常态下提高的主要原因是声悬浮作用降低引起定子和转子的动态接触力增加所致。     

结构参数对车辆薄壁结构碰撞性能影响的研究

利用显式有限元方法对不同厚度、不同截面形状以及不同预变形的薄壁结构碰撞性进行了仿真计算,通过分析比较,得到结构参数对碰撞性能的影响以及薄壁结构的基本碰撞规律,为车辆耐碰撞性能的设计奠定了基础。     

隔声结构的声学性能试验及仿真分析

试验测量和仿真计算是隔声结构声学性能研究的重要方法.首先对隔声结构声学性能试验测量的混响室法和阻抗管法进行介绍,并分析2种方法的优缺点以及适用范围,为隔声性能测量方法的选择提供依据;同时,将有限元法和统计能量分析法用于隔声结构的声学性能仿真计算,并将计算结果与实验测量结果以及理论公式计算结果进行对比分析,结果表明,理论公式的计算结果与试验测量结果相差很大,特别在吻合频率附近,只能对隔声结构的声学性能进行初步预估.而有限元法和统计能量分析法计算结果与试验测量结果吻合良好,适用于隔声结构的声学性能仿真计算.     

航空高筋薄壁类铝合金零件加工方法研究

随着航空高筋薄壁类铝合金零件在飞机设计中的不断应用,其加工制造方法受到行业内的普遍关注。本文以高筋薄壁类铝合金零件的工艺分析及加工策略为主线,阐述了几种结构特殊（腹板、侧壁超薄和筋条超高等）且工艺性较差、加工难度较大的薄壁结构件,通过各类非常规的加工方法、手段及编程策略,实现了优质高效的加工效果,为今后类似的航空高筋薄壁零件的加工和改进积累了宝贵的实践经验。     

共形薄壁腔体结构件机械加工技术研究

文中以某机载产品的典型共形薄壁腔体结构件为研制载体,分析了在薄壁件机械加工中影响其加工质量和加工效率的一些重要因素,研究重点包括工艺策略、刀具选择、应力释放及装夹方式等。总结了提高共形薄壁件加工精度和控制变形量的工艺优化方法和实施措施,并通过试验加工,验证了该工艺优化方法和工艺措施的有效性。     

Computational and experimental methods in the systems of current diagnostics of thermal stresses in elements of machines and structures

Application of the inverse-problem methods of experimental mechanics for diagnosing thermal states of elements and structures is considered. An inverse problem of nonstationary thermal conductivity and an iteration method for its solution on the basis of an alternating procedure are studied.     

Optimization of Parameters of Electromagnetic-Acoustic Thickness Gauges for Thin-Wall Structures

Operation of ultrasonic thickness gauges with electromagnetic-acoustic (EMA) detection and excitation has been studied. The mode of operation using testing signals in the form of trains of two to four acoustic shear oscillations is preferable to the impact excitation in tests of thin-wall pieces (pipes, sheets, T-bars, etc.). The carrier frequency can be up to 8 MHz. The results of the reported study have been used in designing EMA thickness gauges for pipes.     

A Spectral–Thermal Bench with a Special Fiber-Optic Probe–Objective for Measuring Diffuse-Reflection Spectra

The results of tests of a new fiber-optic probe–objective for measuring both IR diffuse-reflection spectra and other types of spectra of solids at various temperatures are presented. In comparison with the conventional devices, the new scheme for measuring diffuse-reflection spectra has such advantages as the minimum distortion of spectra by the specular and Fresnel diffuse components of the reflection from surface irregularities and the linearity of the concentration dependences. The use of a fiber-optic probe–objective provides the ability for the simultaneous analysis of the solid phase and outgoing gases with increasing temperature and calibration of the spectral methods using the thermogravimetric-analysis data. An example of monitoring the process of drying catalysts in laboratory studies when analyzing composite and other materials is used to consider the prospects for using the probe–objective.     

便携式水听器测试仪的研究与实现

水声声压是声学测量中应用最广泛的参数,声学计量检定系统中对水听器声压灵敏度的校准有多种方法.传统的水声测试系统使用工业计算机及水声水池,体积相对庞大.伴随着新型器件、新材料和数据采集器的应用,利用比较法校准原理及声波导管理论,以嵌入式系统为核心,设计一种能够在普通密闭腔体内完成测试的便携式水听器测试仪.可以进行直流电阻、交流阻抗、灵敏度、极性测量,且具有扫频及自动校准功能,软件界面友好.对密闭声场的仿真及实测结果表明,该仪器测量以密闭声场代替水声水池,电压测量精度为0.5 mV,电压灵敏度级的测量精度高于0.8 dB,满足产品生产测试要求,应用前景良好.     

Recent advances in magnetic force microscopy

During the past ten years magnetic force microscopy (MFM) has become probably the most powerful general-purpose method for magnetic imaging. MFM can be applied under various environmental conditions and requires only little sample preparation. Basic research on magnetic materials as well as the mentioned industrial applications create an increasing demand for high-resolution magnetic imaging methods. This contribution will review some new concepts which have been realized in the field of advanced probe preparation, based on electron beam methods in order to improve the spatial resolution beyond 100nm. It is shown that the advanced probes allow high-resolution imaging of magnetic fine structures within thin film permalloy elements exhibiting a complicated cooperative magnetization reversal process. These investigations are of importance for various concepts underlying modern magnetic data storage developments. Furthermore, we present some developments of MFM to suit the needs of the magnetic recording industry.     

A Universal Fiber-Optic Spectroscope for Studying the Modulated Reflection of Semiconductor Structures

A universal fiber-optic spectroscope has been developed that allows one to study state-of-the-art semiconductor structures by various methods employing the modulated reflection of light. Among these are both the well-known traditional methods of photoreflection and electroreflection and the new methods of longitudinal current modulated reflection and below-bandgap photoreflection. The possibilities of the spectroscope are demonstrated by studies of the semiconductor structures used to manufacture high electron mobility transistors and high-power semiconductor lasers.     

Determination of Electric and Mechanical Characteristics of Piezoceramic Elements

Piezoceramic elements (PCE) have been widely used in manufacture of various emitters and receivers of acoustic waves, filters, delay lines, and in other devices, such as piezoelectric transformers and drivers, etc. In order to improve their performance and widen the domain of PCE applications, methods and instruments are required for rapid and accurate determination of their parameters. The paper describes a technique for automated measurements and calculations of electric and mechanical characteristics of piezoceramic materials based on dynamic methods [1, 2] and American IEEE standards [3, 4]. The technique can be used in measuring rated parameters of PCE. In addition, we attempted to refine formulas prescribed by the State Standard GOST 12370-80 [2] using the theory of piezoelectric effects [5–8].     

Application of the Spectral Analysis of Acoustic Emission Signals to Studies of Vulnerability of TiN Coatings on Steel Substrates

A technique has been suggested for processing spectra of acoustic emission (AE) signals based on a signal classification using shapes of normalized spectral density curves. This enables one to calculate averaged spectral images of AE signal groups, which characterize specific types of AE sources, and to estimate intensities of various emission sources on various stages of deformation. The suggested technique has been used in estimating the TiN vulnerability when it is strained concurrently with the substrate.     

大倾斜角薄壁结构激光近净成形实验研究

针对复杂装备零件的快速成形及修复问题，提出了一种在激光束与垂直方向之间设置预设夹角的方法，开展了不同预设夹角下无支撑倾斜薄壁结构的成形实验，研究了倾斜薄壁结构的大角度成形机理，给出了预设夹角范围的选择依据，以实现无支撑大倾斜角薄壁结构的成形。研究结果表明：成形过程中无支撑熔融粉末发生坍塌是导致最终成形结构形貌及角度成形精度不高的主要原因；当设定的预设夹角使得激光束与倾斜薄壁结构之间的夹角小于30°时，成形得到的无支撑倾斜薄壁结构形貌良好且实际倾斜角度与设计角度较吻合。给定工艺条件下，采用预设夹角的方式，最终成形得到了倾斜角度约为60°的倾斜薄壁结构，突破了激光近净成形方法成形无支撑倾斜薄壁结构的倾斜极限，成功获得了三元叶片样件。     

All fiber based multispeckle modality endoscopic system for imaging medical cavities

Disease detection in body cavities, such as the detection of abnormal growths in the colon path, has been illustrated here using an image fiber guided catheter based multispeckle modality endoscopic system. An all fiber-optic approach for the illumination and imaging of the inner cavity walls is adopted here. An endoscope probe to carry the illumination fibers as well as the imaging lens-image fiber unit is designed and custom fabricated in order to operate the probe in its various direction sensitive configurations. This is facilitated by the selection of suitable optical elements such as beam combiner and biprism at the probe proximal end. Experimental investigations were carried out using the endoscope system employing phantom model of colon as the test specimen that has normal and abnormal (representing growth) regions and the obtained results indicated the system effectiveness in identifying the abnormal growths at an early stage.     

Technique of Measurements of Elastic Wave Attenuation Parameters

Certain methodical aspects of using one of the active methods of acoustic testing of materials and products, namely, measurements of the frequency dependence of the attenuation coefficient are considered when the dependence of recorded results on the physical differences between the measurement channels is eliminated. The attenuation coefficients of transverse and longitudinal ultrasonic waves are estimated under the laboratory conditions and the problems of predicting the remaining lifetime on the basis of attenuation of surface acoustic waves in plates subjected to alternating bending in the low-cycle fatigue domain are discussed.     

基于AIC信息准则的Delta T声发射源定位方法

疲劳断裂是金属结构中的主要失效形式,而金属结构中的早期疲劳断裂信号通常难以检测。TOA方法是常用的声发射定位源方法,但是声波传播过程中波速变换和路径的复杂性对其结果影响很大。运用Delta T声发射源定位方法,用断铅实验模拟声发射源,用AIC信息准则对到达时间进行优化,通过使用差值求源点坐标和图像处理的方法,求得声发射源坐标。通过在平板上的实验,比较两种源定位方法在不同结构中的定位结果,分析定位误差,结果表明图像处理方法更为优秀。     

大型结构地面模态试验测点选择与优化

为了解决一般传统的优化算法对于大型结构测点的优化配置的失效问题,针对传统优化算法的缺点,对大型结构的模型缩聚技术做了进一步的改进和完善。引入了一个反映高阶模态贡献比例的权重系数,由此提出了一种基于有效独立法的混合优化算法:基于有效独立法的加权平均模态应变能系数法。经火箭仿真实例对上述方法及Guyan缩聚基于模态应变能系数有效独立法、改进后Guyan缩聚基于模态应变能系数有效独立法得到的测点配置效果进行了比较。结果表明:提出的测点优化算法有效地防止了测点分布聚集现象,而且都最大可能保证了所有模态应变能的贡献和较优布置测点具有较大能量的要求,并用实际的GARTEUR飞机模型对该方法进行了模态试验验证。试验结果表明,该算法保证了监测模态的完整性和线性无关性。