复合材料层压板钻孔分层激光超声检测方法

飞机复合材料结构钻孔分层的定位、定量检测是无损检测领域的难点之一,也是航空制造领域亟待解决的安全问题之一,激光超声检测技术是解决该问题的可能途径。试验验证利用激光超声检测复合材料钻孔分层的技术可行性。制备复合材料层压板钻孔试样,研究热弹性条件下脉冲激光在复合材料中产生超声波的宽频带特性,提取出满足检测灵敏度、分辨力要求并具有良好信噪比的超声信号;分析近孔边缘分层界面对声传播规律的影响,得出钻孔边缘分层缺陷的激光超声表征方法;采用脉冲反射法、透射法对复合材料钻孔试样进行激光超声C扫描检测,获得钻孔分层缺陷的形貌、尺寸和位置特征。研究结果表明,激光超声检测技术是解决飞机复合材料结构钻孔分层检测问题的有效手段。     

Ultrasonic characterization on sequences of CFRP composites based on modeling and motorized system

Composites are a material class for which nondestructive material property characterization is as important as flaw detection. Laminates of fiber reinforced composites often possess strong in-plane elastic anisotropy attributable to the specific fiber orientation and layup sequence when waves are propagating in the thickness direction of composite laminates. So the layup orientation greatly influences its properties in a composite laminate. It could result in the part being rejected and discarded if the layup orientation of a ply is misaligned. A nondestructive technique would be very beneficial, which could be used to test the part after curing and requires less time than the optical test. Therefore a ply-by-ply vector decomposition model has been developed, simplified, and implemented for composite laminates fabricated from unidirectional plies. This model decomposes the transmission of a linearly polarized ultrasound wave into orthogonal components through each ply of a laminate. Also in order to develop these methods into practical inspection tools, motorized system have been developed for different measurement modalities for acquiring ultrasonic signals as a function of in-plane angle. It is found that high probability shows between the model and tests developed in characterizing cured layups of the laminates.     

Means for Increasing the Sensitivity of Acoustic Probing when Studying the Structure of Metals

As exemplified by the use of different approaches to processing the results of probing metals with elastic waves, means have been studied for increasing the sensitivity of the ultrasonic method. Representing processes that determine the effect that a medium has on the parameters of an elastic wave by a statistical model in the form of a Dirichlet distribution makes it possible to numerically characterize changes in the structure of a probing pulse and to improve the understanding of phenomena that occur when an elastic wave interacts with a medium, with the degree of material damage taken into account.     

Applications of electromagnetic acoustic transducers in the NDE of non-conducting composite materials

An electromagnetic acoustic transducers (EMAT) can usually generate or detect an ultrasonic wave in an electrically conducting material across a small gap. The transducer is a unique ultrasonic EMAT probe that does not require a couplant or gel. Therefore it can be applied in a noncontact mode with a high degree of reproducibility. Shear waves and Lamb waves can be easily generated with EMATs in single-sided access. However, the application of EMAT has been limited to electrically conducting materials. In this work, EMAT was applied to the inspection of nonconducting composites by adhering a removable aluminum foil tape on the part surface. Ultrasonic waves generated in the aluminum layer by the EMAT readily propagated into the nonconducting composite. The reversed process was used in the reception of ultrasonic waves by EMAT. For composites that contained surface metallizations (e. g., metal foil or mesh) for lightning protection and electromagnetic interference (EMI) purposes, EMAT probes were placed directly on the composite surface. Finally, EMAT-generated, normal-incidence shear waves were used for the inspection of “green” laminates before curing to detect errors in ply orientation and layup sequence. This study was supported by the Center for Nondestructive Evaluation at Iowa State University, 1A, U. S. A. and by the Factory Automation Research Center for Parts of Vehicles (FACPOV) in Chosun University, Kwangju, Korea, designated by KOSEF     

超声波传输时间精密测量方法及应用研究

根据超声波回波信号是一个变幅周期性信号这一特点,提出一种用数字细分来精密测量超声波传输时间的方法,阐明了超声波换能器驱动电路原理及利用FPGA电路和高分辨率A/D电路通过高频采样来实现这一方法的原理,并采用该方法和电路设计了超声波流量计。指出超声波传输时间测量的分辨率取决于超声波信号的频率和A/D电路的分辨率,为保证测量精度,应尽可能采用较高的采样频率。超声波传输时间的测量综合了全部回波信号采样数据,有很好的可靠性和很强的抗干扰能力。     

用于气象观测的光纤结冰探测仪

飞机结冰会对其飞行安全造成威胁,潜在结冰区可通过观测气象结冰条件来判断。设计了一种新型的光纤结冰探测仪,它主要由结冰传感器和解调器组成。其中,结冰传感器采用反射式和透射式光纤结冰传感器;解调器利用单片机MSP430实现数字取样积分算法,具有较强的微弱光信号检测能力。该探测仪借助探空仪升空,能够测量冰厚,且具有抗干扰、体积小、成本低、质量轻和功耗低等优势。试验表明,该探测仪具有灵敏度高、量程宽、线性度好等优点,且具备冰型区分能力,因而具有良好的应用前景。     

Train wheel diagnostics by laser ultrasonics

The integrity of the wheel is very important for the safety of railway. In this paper a laser-ultrasonic diagnostic measurement procedure has been designed for the inspection of the train wheels with the aid of a FE-model simulating the ultrasound propagation within the wheel itself.The laser-ultrasonic method exploits an air-coupled ultrasonic probe that detects the ultrasonic waves generated by a high-energy pulsed laser. As a result, the measurement chain is completely non-contact, from generation to detection, this making it possible to considerably speed up the testing set-up time and make it more flexible. This is an important advantage with respect to the conventional NDT technologies currently applied to train component diagnostics, as contact phase array methods. Laser ultrasonics is a complete remote technique since both the laser source and the receiving probe are installed in the proximity of the wheel directly on the bogie and therefore it is a more flexible technology with respect to standard techniques applied for wheel train diagnostics, as phased array.The applications of laser-ultrasonic technique available in the state-of-the-art work with high energy ultrasonic waves to guarantee good signal to noise ratio. Therefore, conventional laser-ultrasonic systems operates under ablative regime that assures high energy ultrasonic waves generation. On the other hand, the ablation produces damages on the surface of the component inspected. In this paper, it has been demonstrated that it is possible to work with lower energy waves, i.e. in the limit between ablative and thermo-elastic regime, if the experiment is properly designed on the basis of a numerical model. This operation regime allowed to guarantee a material removal below the threshold admitted in rail wheel application. The diagnostic procedure developed has been applied for the inspection of train wheels provided by the Italian railway company Trenitalia, on which dominant wheel failure cracks have been expressly created.     

A broadband spectroscopy method for ultrasonic wave velocity measurement under high pressure

A broadband spectroscopy method is proposed to measure the ultrasonic wave phase velocity of Z-cut quartz under high pressure up to 4.7 GPa. The sample is in a hydrostatic circumstance under high pressure, and we can get longitudinal wave and shear wave signals simultaneously in our work. By fast Fourier transform of received signals, the spectrum and phase of the received signals could be obtained. After unwrapping the phase of the received signals, the travel time of ultrasonic wave in the sample could be obtained, and the ultrasonic wave phase velocity could also be resolved after data processing. The elastic constant of measurement under high pressure is also compared with previous studies. This broadband spectroscopy method is a valid method to get ultrasonic wave travel parameters, and it could be applied for elasticity study of materials under high pressure.     

Separation of waves governed by the one-dimensional wave equation—a stochastic systems approach

In various applications it is of interest to extract the wave traveling in a certain direction of a medium. As waves that propagate in different directions generally overlap, it is not possible to directly measure the desired wave. This paper presents techniques for separation of waves governed by the one-dimensional wave equation in the presence of measurement noise. The derived estimators are based on stochastic modeling of the waves and measurement noise, state space representations and optimal state estimation. The treatment of measurement noise is of crucial importance since it fundamentally limits the performance of wave separation. The derived estimators are compared and evaluated through analytical results and computer simulations. The efficiency of the wave estimation does not only depend on the magnitudes of the waves and the noise, but also on the structure of the estimator, the number of sensors and the spacing between sensors. It is shown that the wave traveling in a certain direction can be estimated with high accuracy without amplification of the measurement noise.     

超声导波在H型钢结构损伤识别中的应用

针对H型钢在损伤情况下对超声导波的影响,提出基于超声导波的结构健康监测方法,并探讨了应用超声导波检测技术在H型钢中对结构损伤识别的可行性及其识别能力。采用中心频率为87.5kHz的波形为汉宁窗调幅3.5个周期正弦曲线作为激励波形,应用商业有限元软件ABAQUS对导波在H型钢构件中的传播进行了仿真,同时对无损伤以及有损伤的仿真模型进行实验验证。实验中利用压电材料锆钛酸铝(piezoelectric lead zirconate titanate,简称PZT)换能器来激发和接收在H型钢中传播的导波信号,借助于Morlet小波时频分析等方法对仿真和实验采集到的信号进行处理,并比较实验结果与仿真结果的吻合度。最后分析H型钢中损伤的大小等因素对损伤识别的影响,以及超声导波在H型钢中的损伤识别能力。     

Analysis of ultrasonic fields and flaw detection in aluminum single crystals based on laser detection technique

Features of ultrasonic testing of aluminum single crystals are discussed. Ultrasonic waves were generated by PZTs, and acoustic fields on the opposite surfaces of single crystals were analyzed using a laser interferometer. Flaws opening on surfaces were detected in single crystals grown along the [001] axis. Features of elastic strain fields due to waves propagating along the [111] axis have been studied.     

变化环境下的超声导波结构健康监测研究进展

超声导波结构健康监测(Structural health monitoring,SHM)在大规模板和管结构的缺陷诊断中是一个极具吸引力的检测技术。不同研究者均证实环境和操作条件变化,特别是温度和外加载荷变化会掩盖由缺陷引起的信号变化从而限制SHM系统的性能。分别就环境变化中温度和外加载荷对SHM系统中超声导波传播机理的影响进行综述:环境温度的变化会引起样本热膨胀系数和弹性模量的改变,进而影响超声导波在结构中的传播,且相比于超声纵向导波,横波对温度的敏感度较低;外加载荷对导波传播的影响主要体现在时移、幅值及相位的变化上。针对温度变化对导波结构健康监测造成的影响,详细阐述温度补偿法的研究进展,为更好地辨识由缺陷引起的变化和由周围环境引起的良性变化奠定理论基础,为后续超声导波SHM的研究指明方向。     

基于匹配追踪的蜂窝夹层复合材料损伤检测

基于Lamb波和匹配追踪时频分析方法,提出一种损伤成像方法,对蜂窝夹层复合材料结构进行损伤监测.首先针对Lamb波传播的特点,提出了匹配追踪方法的快速实现方案,该方法能准确地匹配失真变形的窄带脉冲信号,并识别Lamb波的模态;然后对由压电传感器采集到的Lamb波信号,采用匹配追踪方法提取特征信息,得到Lamb波的能量分布;在此基础上,考虑Lamb波在各向异性结构中传播速度的影响,将损伤处的散射波能量分布和各像素点对比度联系起来,得到损伤图像,将损伤的情况可视化.通过蜂窝夹层复合材料结构实验验证了该方法的可行性和有效性.     

基于ZigBee无线通信技术的河流水位监测系统

针对目前国内的河流水位监测现状,文中提出了一种将ZigBee无线通信技术和超声波测量技术相结合的河流水位监测系统。该系统将超声波测量模块与无线传感器节点相结合,充分发挥无线传感器体积小、功耗低、易于扩展的特点,具有广阔的应用前景。     

Fringe counting method for synthetic phase with frequency-modulated laser diodes

Fringe counting method with laser diodes (LDs) for displacement measurement has been constructed. Two LDs are frequency modulated by mutually inverted sawtooth currents on an unbalanced two-beam interferometer. The mutually inverted sawtooth-current modulation of LDs produces interference fringe signals with opposite signs for respective wavelengths. The two fringe signals are fed to an electronic mixer to produce a synthetic fringe signal with a reduced sensitivity to the synthetic wavelength. Synthetic fringe pulses derived from the synthetic fringe signal make a fringe counting system possible for faster movement of the tested mirror.     

Determining the Speed of Longitudinal Waves in an Isotropic Homogeneous Welded Joint Using Echo Signals Measured by Two Antenna Arrays

A technique is proposed for measuring the speed of longitudinal ultrasonic waves in a homogeneous welded joint, based on comparing measured and computed echo signals reflected from the bottom of a test object when using two antenna arrays mounted on prisms and operating in the double scanning mode. The effect of errors in setting the values of such parameters as the distance between the antenna arrays, test-object thickness, and others on the accuracy of calculating the wave velocity in the weld has been analyzed. Results of numerical and model experiments on calculating the wave velocity in the welded joint are presented. In a model experiment, the technique has made it possible to measure the speed of longitudinal waves in the weld model with an error of less than 0.7%. The method can be used to find the initial approximation in a nonlinear inverse problem of tomographic inspection of welded joints in the wave approximation.     

An experimental method to measure the layer thickness and wave velocity of copper–steel composite board without interface echo

Thickness of each medium layer and velocity of ultrasonic wave propagation in each medium layer of the two-layer composite medium were measured simultaneously based on the method to collect phase information from continuous echo signals on front surface and undersurface. Such measurement was implemented under no interface echo and fixed total thickness of the testpiece. The method can be applied to any two kinds of two-layer composite medium. The paper only used a 35 mm thick copper–steel composite board as an experimental example. Calculated results demonstrated that measuring errors of both thickness and velocity of ultrasonic wave propagation are smaller than 0.2%, indicating the effectiveness of the proposed measurement method.     

A hydrophysical laser-interference complex

An upgraded laser measurer of hydrosphere pressure variations is described. By mounting new pressure and temperature sensors and optimizing the design of the submersible instrument, it has become possible to considerably increase the measurement accuracy of amplitude?frequency characteristic describing variations in the pressure, aqueous medium temperature, and wave amplitudes at the sea surface in the infrasonic and audio ranges and to correct plotted time dependences of the pressure variations in view of the variations in the interferometer and outboard water temperatures. For long-term (up to 40 h) self-contained operation of the complex to be guaranteed, a versatile floating container has been developed. This container is equipped with high-power batteries and data acquisition systems receiving information from the sensors and can be joined to a hermetically sealed connector of the complex instead of the cable line used for communication between the complex and coast equipment.     

Integration of fiber-optic sensors in measuring machines

In last years, optical metrology due to its capability in miniaturization and sensitivity became the primary solution in measurement of complex geometries and fragile pieces. Here, we propose a promising approach to perform highly accurate distance measurements using low-coherence fiber-optic sensors for quality inspection of nozzle orifices in fuel injection systems. In this effort, we develop an adaptive image processing algorithm in MATLAB and install the necessary hardware on a form tester to accelerate and simplify the aligning process. As a result, the repeatability of measurements is one order of magnitude improved while the standard deviation is almost 60% reduced.     

Selecting Optimum Parameters of Ultrasonic Noncontact Shadow Method for Testing Products Made of Polymer Composite Materials

Russian Journal of Nondestructive Testing - It has been shown that in order to increase the sensitivity of ultrasonic noncontact shadow testing of products made of polymer composite materials...