Review on quality assurance along the CFRP value chain – Non-destructive testing of fabrics,preforms and CFRP by HF radio wave techniques

Eddy current testing is well established for non-destructive testing of electrical conductive materials [1]. The development of radio frequency (RF) eddy current technology with frequency ranges up to 100 MHz made it possible to extend the classical fields of application even towards less conductive materials like CFRP [2][3](Table 2). It turns out that RF eddy current technology on CFRP generates a growing number of valuable information for comprehensive material diagnostic. Both permittivity and conductivity of CFRP influence the complex impedance measured with RF eddy current devices. The electrical conductivity contains information about fiber texture like orientations, gaps or undulations in a multilayered material. The permittivity characterization influenced by dielectric properties allows the determination of local curing defects on CFRP e.g. hot spots, thermal impacts or polymer degradation. An explanation for that effect is seen in the measurement frequency range and the capacitive structure of the carbon rovings. Using radio wave frequencies for testing, the effect of displacement currents cannot be neglected anymore. The capacitive structures formed by the carbon rovings is supposed to further strengthen the dielectric influences on eddy current measurement signal [3]. This report gives an overview of several realized applications and should be understood as a general introduction of CFRP testing by HF Radio Wave techniques.     

A Flexible Conformal Piezoresistive Sensor Based on Electrospinning for Deformation Monitoring of Carbon Fiber-Reinforced Polymer

Carbon fiber-reinforced polymer (CFRP) materials are widely applied in various areas as key structure components. The structural health monitoring of the CFRP components is crucial to prevent catastrophic failure. However, the nonplane surfaces of CFRP components hinder the attaching of monitoring sensors with hard substrates. Therefore, the substrate conditions for sensor preparation are mainly considered in this study. To adapt the proposed sensors to the curved substrate, including nondevelopable surfaces, electrospinning method is used to prepare conformal piezoresistive fiber films, in which polymethyl methacrylate is served as the matrix and carbon nanotubes are utilized as the conductive filler. The piezoresistive fibers covered on CFRP substrates have a gauge factor up to 207.95 and can response to the strain less than 0.05%. Moreover, the sensor also has high durability and the ability to follow the dynamic excitation signals with as high as 50 Hz.     

Implementation of a versatile research data acquisition system using a commercially available medical ultrasound scanner

This paper describes the design and implementation of a versatile, open-architecture research data acquisition system using a commercially available medical ultrasound scanner. The open architecture will allow researchers and clinicians to rapidly develop applications and move them relatively easy to the clinic. The system consists of a standard PC equipped with a camera link and an ultrasound scanner equipped with a research interface. The ultrasound scanner is an easy-to-use imaging device that is capable of generating high-quality images. In addition to supporting the acquisition of multiple data types, such as B-mode, M-mode, pulsed Doppler, and color flow imaging, the machine provides users with full control over imaging parameters such as transmit level, excitation waveform, beam angle, and focal depth. Beamformed RF data can be acquired from regions of interest throughout the image plane and stored to a file with a simple button press. For clinical trials and investigational purposes, when an identical image plane is desired for both an experimental and a reference data set, interleaved data can be captured. This form of data acquisition allows switching between multiple setups while maintaining identical transducer, scanner, region of interest, and recording time. Data acquisition is controlled through a graphical user interface running on the PC. This program implements an interface for third-party software to interact with the application. A software development toolkit is developed to give researchers and clinicians the ability to utilize third-party software for data analysis and flexible manipulation of control parameters. Because of the advantages of speed of acquisition and clinical benefit, research projects have successfully used the system to test and implement their customized solutions for different applications. Three examples of system use are presented in this paper: evaluation of synthetic aperture sequential beamformation, transverse oscillation for blood velocity estimation, and acquisition of spectral velocity data for evaluating aortic aneurysms.     

Ultrasonic scanner for in vivo measurement of cancellous bone properties from backscattered data

A dedicated ultrasonic scanner for acquiring RF echoes backscattered from the trabecular bone was developed. The design of device is based on the goal of minimizing of custom electronics and computations executed solely on the main computer processor and the graphics card. The electronic encoder-digitizer module executing all of the transmission and reception functions is based on a single low-cost field programmable gate array (FPGA). The scanner is equipped with a mechanical sector-scan probe with a concave transducer with 50 mm focal length, center frequency of 1.5 MHz and 60% bandwidth at -6 dB. The example of femoral neck bone examination shows that the scanner can provide ultrasonic data from deeply located bones with the ultrasound penetrating the trabecular bone up to a depth of 20 mm. It is also shown that the RF echo data acquired with the scanner allow for the estimation of attenuation coefficient and frequency dependence of backscattering coefficient of trabecular bone. The values of the calculated parameters are in the range of corresponding in vitro data from the literature but their variation is relatively high.     

Fatigue properties of multifunctional metal‐ and carbon‐fibre‐reinforced polymers and intrinsic capabilities for damage monitoring

Carbon‐fibre‐reinforced polymers (CFRP) structures offer enhanced lightweight potential in comparison with monolithic metallic concepts. Brittle failure behaviour and the insufficient level of electrical conductivity limit the lightweight potential of composites. One promising new approach to solve these issues is the additional integration of metal fibres. Structural components are subjected to cyclic loads during their lifetime. Therefore, the present study focuses on the influence of additional steel fibre reinforcement on the fatigue behaviour of CFRP laminates. Magnetic properties are determined because of the deformation‐induced phase transformation of the chosen austenitic steel fibres, which are also applied as intrinsic damage sensors. Interrupted fatigue tests are carried out accompanied by scanning electron microscopy to obtain differences in failure mechanisms. Beside a detailed overview of the steel fibre influence on the fatigue properties of conventional CFRP structures, the functional evidence of a new method for nondestructive testing by a magnet inductive measuring device is shown.     

Fast, micrometer scale characterization of group-III nitrides with laboratory X-ray diffraction

We have designed a convergent beam, concurrent detection X-ray diffractometer. The instrument was built by Bruker AXS and is equipped with a rotating anode generator, a Johannson monochromator crystal for beam focusing, and a Soller slit arrangement in combination with a knife edge in front of the sample which defines the illuminated area on the sample. Samples up to 12 in. can be mounted on the sample stage of a D8 Eulerian cradle. A large area detector enables rapid simultaneous detection of the diffracted intensity. The instruments allow for a fast evaluation of large samples at high lateral resolution. In favourable cases lateral resolution down to 1 μm is possible. Furthermore a grazing incidence diffractometer has been developed which allows for depth-dependent measurements at high intensity.     

Characterization of Capacitance Standards at High Frequency at National Physical Laboratory,India

Four-terminal-pair air dielectric capacitance standards with nominal values of 1000 and 100 pF have been characterized up-to 10 MHz at NPLI. The procedure employed involves the determination of all capacitive and inductive parameters of the simple electrical-equivalent-circuit-model of these capacitance standards. The effective capacitance of each standard has also been computed as a function of frequency from 1 kHz to 10 MHz. The capacitive parameters have been measured at 1 kHz while inductive parameters have been estimated up to 10 MHz using linear regression analysis by employing least-squares-approximation method. The paper highlights the computation procedure of impedance terms which further requires the determination of various capacitive and inductive terms involved in the calculation of effective capacitance. The method employed for the estimation of inductive parameters as a function of frequency is also discussed in detail. The present work will help in the establishment of metrological traceability of capacitance standards at high-frequency at NPLI which will be further used to establish calibration facility for LCR meters and RF impedance analyzers for capacitance parameter up-to 10 MHz.     

New Noncontacting Inductive Analog Proximity and Inductive Linear Displacement Sensors for Industrial Automation

Noncontacting inductive sensors are applicable on a large scale for position detection or travel measurement in industrial applications. Reasons for such broad acceptance in many sectors of industry are noncontact and wear-free sensing of the target (any metal object), reliability and robustness, resistance to fouling, water tightness and compact size. The present work is intended to be a systematic, complete, and consistent presentation of the technological innovations, recent implementations and current trends regarding the analog distance and travel sensing offered by noncontacting inductive sensors for industrial applications. It starts with the fundamentals of inductive sensing and presents the physical basics gained by modern analytic and simulation methods, as well as high-level integrated circuits for inductive sensors. The following sections deal with present-day inductive analog proximity sensors and with the distinctive technological innovation offered by the new inductive linear displacement sensors and with miniaturization results achieved through consistent integration.     

Improved Test Methodology for Production Testing of RF Switches Using a New Relative Measurement Technique

High-volume production testing using automatic test equipment (ATE) is an important part of the integrated circuit manufacturing industry, where it allows products to be rigorously characterized to ensure conformity with their data-sheet specifications. When used in production, the accuracy and repeatability of the ATE must itself be understood so that the final measurements are a true reflection of the underlying product performance and are not adversely influenced by variations or inaccuracies in the ATE setup. This paper reports on the application of the ATE to production testing of CMOS solid-state RF switches operating at 1 GHz and the steps that have been taken to remove sources of variation from the measurement setup. In particular, a calibration path based on the solid-state GaAs switches, which shares most of the RF signal path with the device under test (DUT), is described. The introduction of the calibration path reduces the variability of the measurement system by up to 60%, thus ensuring the suitability of the new setup for an ongoing high-volume production test.     

一个高温持久/蠕变测控温及试验管理系统

介绍了采用测控分开形式对近百台五六十年代制造的高温持久/蠕变试验机进行测控温系统改造的工作.改造后的控温系统创造了不同热电偶数量(测控温共偶,1～3支)都可实现对试样温度和梯度的稳定控制,系统具有较强抗外界干扰能力,而且控温过程中对电网无干扰.测量系统测量误差≤±0.1%FS.测控温系统采取单炉闭环控制、30台集中巡回...     

Short time tensile behavior of unidirectional glass and carbon fiber reinforced polymer laminates with curved shapes

A newly developed confining system for rectangular columns required a wrapping, which sustained a large amount of parasitic bending due to the curved shape of the laminates at the cross-section corners. To investigate the effect of parasitic bending on unidirectional carbon (CFRP) and glass fiber (GFRP) reinforced polymer laminates, 4 ply coupons were laminated with a semi-elastic hybrid resin and cured in a curved shape. During the tensile tests, the curved coupons stretched and failed after further loading. Due to the parasitic bending, occurring during stretching, the tensile resistance was reduced by 48% for the CFRP and by only 18% for the GFRP coupons. Tests with high-strength, high-modulus epoxy resin laminated GFRP coupons were drawn upon and compared with the semi-elastic hybrid resin laminated GFRP coupons. There is a beneficial effect on the tensile resistance with the use of semi-elastic hybrid resin.     

Characterization of the Response of CaWO4 on Recoiling Nuclei from Surface Alpha Decays

A potentially harmful background for experiments attempting direct dark matter detection like the CRESST (= Cryogenic Rare Event Search with Superconducting Thermometers) experiment is caused by recoiling nuclei from ²¹⁰Po alpha decays on surfaces close to the detector. In order to characterize this kind of background in CRESST, calibration measurements have been performed at the TU München. A for this purpose an optimized version of the CRESST detector has been developed consisting of a 38 g CaWO₄ crystal and a separate cryogenic light detector, both equipped with Ir/Au transition edge sensors (TESs). The simultaneous measurement of the phonon signal and the scintillation light from the CaWO₄ crystal allows to discriminate between electron and nuclear recoils using their different light outputs. The unexpected results of a first measurement with a ²¹⁰Po source can be understood with the help of a Monte Carlo simulation performed for a similar system.      

Curved quadratic triangular degenerated‐ and solid‐shell elements for geometric non‐linear analysis

Compared to the large number of curved quadrilateral degenerated‐ and solid‐shell elements, there are only a very few curved triangular degenerated‐ and solid‐shell elements. Based on the assumed natural strain sampling scheme previously developed for a quadratic degenerated‐shell element for linear analysis, this paper devises geometric non‐linear six‐node degenerated‐shell and twelve‐node solid‐shell elements. Both elements can be curved and are only equipped with the standard nodal d.o.f.s. Careful consideration has been exercised to circumvent various locking phenomena that plague degenerated‐ and solid‐shell elements. Numerical examples are presented to illustrate their efficacy. Copyright © 2003 John Wiley & Sons, Ltd.     

A Study on the Measurement Instrumentation for a Custom-Made Bipendulum Impact Testing Machine

Experimental investigations of structures under impact loads are normally carried out by means of drop-weight testing rigs, which are often tailor made, and require sensors for fast transient measurement of mechanical quantities (namely, force, displacement, velocity, and absorbed energy). Since these tests are quite expensive, time consuming, and, often, not repeatable, the sensors must provide reliable and interpretable results in the first trial. In this paper, a thorough study on the measurement instrumentation suitable to carry out reliable low-velocity impact tests by means of a custom-made bipendulum impact testing machine is presented. Attention has been focused on the choice of the quantities to be measured, on the measurement problem, on the calibration of the instrumentation, and on the mechanical characterization of the impact rig. Original transducers for the measurement of either the initial impact velocity or the impact force have been developed, and their uncertainty has been estimated. The use of polyvinylidene difluoride (PVDF) sensing films for the realization of both single- and multiple-channel tailored dynamic load cells proved to be effective, gaining some significant advantages when compared to the use of more expensive commercial load cells or accelerometers fixed to the impacting mass. The detailed mechanical characterization of the bipendulum impact testing machine accomplished by exploiting the new developed transducers allowed the equivalent mass of the impactor, the alignment between the swinging mass and the sample holder, and the friction loss model to be experimentally assessed. Finally, an example of the application of the instrumented impact testing machine is presented.     

Design of inductive sensors for magnetic testing of steel ropes

The design and operating principles of four inductive sensors for magnetic testing of steel ropes are presented. The magnetic concentrators can maintain the same shape as in Hall-effect leakage flux sensors, but the output signals of the inductive sensors are quite different and depend on the speed of testing. Although the inductive sensors are not as versatile as Hall-effect sensors, they are simpler in operation and can still find applications, especially in the initial and middle stages of the deterioration of the rope.     

用VB实现基于GPIB的自动测试系统

传统的人工校准费时费力,已不能适应实际测试的需求,而且有时测量结果还会受到人为因素的影响。本文通过一个应用于数字移动通信综合测试仪输出小功率测试的完整实例,介绍了在Visual Basic编程环境中用SCPI实现对带有GPIB接口的智能仪器进行程控,组成一个自动测试系统的方法。     

一种抗噪性能较强的电感式传感器测量电路

目的　研究一种在环境恶劣的情况下 ,能准确地将微弱电感量变化转化为电压变化的测量电路 ,以便读出、处理及存储 .方法　采用由两级仪表放大器组成的放大电路来提取电感量变化 ,可以大大提高共模抑制比 .同时采用了可行的抗干扰措施和抑制温漂的措施 ,并通过调相位、调幅值两个电位器达到初始调零的目的 .结果　该测量电路用于坦克扭力轴扭力传感器 ,实验表明它是可行的 .结论　该测量电路对于微弱电感量变化的一般电感传感器具有普遍意义 .     

一种新型的质心测量机构与测量方法

分析了不平衡力矩和多点称重测质心方法,探讨了一种高精度质心测量方法.采用大、小量程十字分布传感器支撑旋转轴系, 设计了一种新型的质心测量机构.利用旋转轴作为质心测量基准,大量程传感器作为等效刀口,小量程传感器测量偏心力,提高了测量灵敏度.进行了测量方法的误差来源分析,结合现有的形心测量技术,研制了一台高精度质心测量设备,并成功应用于产品实测.     

用于薄膜制备的射频宽束离子源的设计

采用射频宽束离子源进行离子束辅助镀膜可以获得高性能的光学薄膜,已越来越得到人们的共识.本文对射频感应线圈的匹配、起弧及三栅离子光学的关键技术进行了重点考虑，并获得了稳定运行的高性能离子源.     

智能CFRP加固RC梁荷载效应的实时模拟与测评

制备了4 根炭纤维复合材料(CFRP) 加固钢筋混凝土(RC) 实验梁, 并在梁内钢筋、混凝土及加固CFRP中预置了布拉格光栅光纤传感器(FBG) 和电阻应变片两种传感器。根据钢筋混凝土理论和ANSYS 有限元软件编制了实验梁受弯荷载效应模拟计算程序。实验表明, 实验梁在受弯承载过程中, 布拉格光栅光纤传感器与传统应变片有完全一致的线性关系; 模拟计算出的实验梁受拉钢筋、压区混凝土应变值及挠度与荷载的关系与CFRP 中FBG的实测值吻合较好。由于对既成RC 结构不能在内部装置传感器(会破坏结构降低抗力) , 采用智能CFRP 加固RC 结构可实现加固和实时健康测评双重功能。