Synchrotron Radiation Tomography for Reconstruction of Layer Structures and Internal Defects of Composite Materials

１　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｌａｙｅｒｓｔｒｕｃｔｕｒｅｓａｎｄｄｅｆｅｃｔｓｏｆａｆｉｂｅｒｒｅｉｎｆｏｒｃｅｄｃｏｍｐｏｓｉｔｅｍａｔｅｒｉａｌａｒｅｔｗｏｉｍｐｏｒｔａｎｔｆａｃｔｏｒｓｆｏｒｉｔｓｓｔｒｅｎｇｔｈａｎｄｄａｍａｇｅｍｅｃｈａｎｉｓｍ．Ｔｒａｄｉｔｉｏｎａｌｌｙ,ｏｎｅｃａｎｇｅｔｓｕｒｆａｃｅｉｎｆｏｒｍａｔｉｏｎｏｆａｃｏｍｐｏｓｉｔｅｂｙｍｅａｎｓｏｆｏｐｔｉｃａｌｍｅｔｒｏｌｏｇｙ,ｓｕｃｈａｓｈｏｌｏｇｒａｐｈｉｃｉｎｔｅｒｆｅｒｏｍｅｔｒｙ,ｓｐｅｃｋｌｅ…     

基于THz-TDS的陶瓷纤维复合材料缺陷检测分析

新型陶瓷纤维复合材料由短切氧化硅纤维及其胶合物经高温烧结得到的一种轻质多孔材料,材料微观结构特性直接影响着宏观结构特性和功能特性.该类材料的孔隙度分布在84％ ～95％ 之间,微观孔径主要集中在100μm范围内,偶尔有少量纳米孔.陶瓷纤维复合材料以其耐高温、低密度、高比强和抗烧蚀等优异性能在超高声速飞行器外层隔热部件得...     

Electrospun fluorescein/polymer composite nanofibers and their photoluminescent properties

Fluorescein/polyvinyl pyrrolidone (PVP) composite nanofibers with different fluorescein loadings (with a weight concentration of 0-5.0%) are fabricated via electrospinning. Morphologies, structures and photoluminescent (PL) properties of these straight, helical or wavelike fibers are characterized by scanning electron microscopy (SEM), fluorescence microscopy and a spectrophotometer. It is found that the maximum emission of the as-spun fluorescein/PVP fibers occurs at 510 nm. The PL intensity of the composite fiber increases with fluorescein concentration, then fluorescence quenching appears when the concentration reaches 1.67%. The mechanism of fluorescence quenching of fluorescein is discussed. In addition, the composite fibers exhibit a much stronger PL intensity than fluorescein/PVP bulk film owing to larger specific surface area, which makes them promising materials for biomedical applications such as probes and sensors.     

Analysis of Spectral Hounsfield Units Curve of Radiolucent and Radiopaque Materials in the Animal Rectum

The purpose of the present study was to assess the general characteristics of images produced by radiolucent and radiopaque materials used for computed tomography scanning of the animal rectum and suggest ideal materials for contrast enhancement between normal and abnormal tissues. The computed tomography system used in this study was 64-multidetector computed tomography. Computed tomography scanning was performed with standard scan parameters for abdominal examination and gemstone spectral image mode using saline, methyl-cellulose, contrast medium, ultrasound gel, and air in addition to radiolucency. Computed tomography values were obtained for each material at different energy levels. Changes in computed tomography values were compared and analyzed. Changes in computed tomography values and volume of each material were examined before and after rectal contrast material administration. Ultrasound gel was found to exhibit a computed tomography value close to the baseline value and a greater degree of contrast, compared with other materials. In image evaluation, methyl-cellulose is considered a useful material in providing contrasting image evidence of rectal diseases. Also, it had a larger volume in the rectum after a computed tomography scan. Thus, methyl-cellulose was a useful contrast medium for computed tomography scan imaging of the rectum.     

Infrared thermography and its application in the NDT of sandwich structures

Thermographic nondestructive testing (NDT) based on the thermal resistance effect of defects is developed for the inspection of delaminated and sandwiched defects embedded in composite structures. The resolution is examined for artificial delaminated defects in carbon-fiber honeycomb structures using conventional infrared radiation heating. The experimental results have demonstrated that radiation heating is effective for revealing defects in the composite structures.An experimental and computational hybrid system is developed for detecting defects in various composite structures. The system consists of an infrared thermal video system which measures the surface temperature distribution of the structure, a computer with a PIP-1024B image board which performs image processing of thermograms, and a HP ink jet XL printer. It is found that this system is readily applicable to the detection of defects located at the interface of the core and skin in honeycomb structures and delaminations in composite materials.     

Defect imaging with elastic waves in inhomogeneous-anisotropic materials with composite geometries

Imaging of defects in composite structures plays an important role in non-destructive testing (NDT) with elastic waves, i.e., ultrasound. Traditionally the imaging of such defects is performed using the synthetic aperture focusing technique (SAFT) algorithm assuming homogeneous isotropic materials. However, if parts of the structure are inhomogeneous and/or anisotropic, this algorithm fail to produce correct results that are needed in order to asses the lifetime of the part under test. Here we present a modification of this algorithm which enables a correct imaging of defects in inhomogeneous and/or anisotropic composite structures, whence it is termed InASAFT. The InASAFT is based on the exact modelling of the structure in order to account for the true nature of the elastic wave propagation using travel time ray tracing techniques. The algorithm is validated upon several numerical and real life examples yielding satisfactory results for imaging of cracks. The modified algorithm suffers, though, from the same difficulties encountered in the SAFT algorithm, namely “ghost” images and eventual lack of clear focused images. However, these artifacts can be identified using a forward wave propagation analysis of the structure.     

Laser-based ultrasonic inspection with a fiber-coupled scanning Cassegrain system

State-of-the-art integrally stiffened composite materials, manufactured for use in the next generation of commercial and military aircraft, are increasingly being used for structural components such as wings and fuselages. However, the complexity of the manufacturing processes can produce small variations in the shape of integrally stiffened composite structures. Thus, a priori knowledge of the nominal part shape often does not provide sufficient accuracy to allow an automated conventional ultrasonic inspection. In contrast, automated inspections of integrally stiffened structures can be performed using laser-based ultrasound techniques since a priori knowledge of the nominal part shape is adequate to scan the laser beams over the structure. This paper addresses the issues associated with the extension of laser-based ultrasonics to inspections in remote and limited access areas, and describes the implementation of a fiber-based remote and limited access LBU inspection system based upon a Cassegrain scanning and optical collection system. The ability to quickly and directly manipulate flexible low mass optical fibers equipped with specialized endoscopic scanning optics make fiber systems an attractive method for the development of limited and remote access inspection systems. The Cassegrain optical system is described in detail and both numerical and experimental validation of the system operational characteristics are presented.     

钇复合氧化物颜料的制备与表征

通过尿素分解法,把三价铬离子掺入到钇铝石榴石Y₃Al₅O₁₂中,采用共沉淀法制备出绿色颜料。扫描电镜测试表明产物颗粒直径在200 nm左右,用XRD测试复合氧化物的结晶相行为,确定主相是钇铝石榴石相,用紫外可见漫反射光谱测试掺杂离子的配位状态和电子跃迁行为,用色度学测试氧化物颜色特征。将复合氧化物颜料颗粒与高分子聚丙烯共混,熔体纺丝,并通过北京同步辐射X射线CT对制得的纤维加以测试,结果表明复合氧化物颜料在高分子基质中得到良好的分散。这种颜料性能稳定,对环境友好,为实现无水印染技术奠定基础,减少纺织印染工业中所排放的污水。     

Polymer composite material characterisation using a laser/air-transducer system

A wide bandwidth 1–3 connectivity piezocomposite air transducer has been used to detect laser-generated ultrasound in a variety of composite materials. Through thickness waveforms in various carbon fibre reinforced polymer (CFRP) composite plates will be presented, as well as a selection of Lamb waves. Signals were also obtained in samples of pultruded glass fibre reinforced composite of different thickness. Using the laser/air-transducer system, images were obtained of machined defects and delaminations by conventional C-scanning methods, and tomographic reconstruction techniques.     

The role of interactions at interfaces of glass-fiber reinforced composites

The performance of glass-fiber reinforced composite materials is strongly dependent on adhesion at the fiber-matrix interface. This study has considered the effect of parameters such as wettability, mechanical interlocking due to diffusion, and specific interactions on adhesion. The surface characteristics of treated and untreated glass fibers were studied by inverse gas chromatography. Donor/acceptor concepts were used to calculate a specific (acid/base) interaction parameter for fiber/matrix pairs. Tensile strengths of composites with Nylon-6,6 and polyethylene correlated with both acid-base and dispersive interactions. Initial attempts were made to separate and quantify contributions to interfacial bonding from dispersive forces, acid/base forces, diffusion and the mechanical interlocking of constituents. Findings were supported by scanning electron microscopy of the fracture surfaces of composite samples.     

空气耦合超声检测复合材料研究综述*

复合材料普遍具有高比强度、高比刚度、高模量、耐腐蚀等优异性能,广泛应用于飞机机翼、导弹外壳、航空发动机壳体等部位。制造和服役过程中各类缺陷影响复合材料的力学性能和服役性能,必须采用有效的方法准确检测和评估复合材料中各类缺陷。空气耦合式超声检测具有完全非接触、非侵入、无损伤和无需耦合剂的特点,能够很好地运用于复合材料的在线和在位检测。该文就近年来空气耦合超声检测技术的研究现状进行了系统综述,简明扼要地分析和介绍了当前空气耦合超声检测的研究热点及进展,重点介绍了1-3型压电复合材料换能器、信号处理技术、相控聚焦式空气耦合超声检测、超声在复合材料的传播特性及其与缺陷交互作用的研究现状,探讨了空气耦合超声无损检测技术与仪器的发展方向,总结了目前空气耦合超声检测的研究热点问题,最后展望了空气耦合超声检测的发展趋势和应用前景。     

Subsurface defect detection in ceramics by high-speed high-resolution optical coherent tomography

We use optical coherence tomography with a new configuration to determine the size and location of subsurface defects in solid ceramic and composite ceramic materials. Cross-sectional subsurface regions either parallel or perpendicular to the surface were examined. We present experimental results showing that the size and distribution of small subsurface defects can be determined with depth and lateral resolutions of 10 and 4 microm, respectively.     

Unsaturated polyester resin (UPR) reinforced with flax fibers,untreated and cold He plasma-treated: thermal,mechanical and DMA studies

Hemp, jute, flax, bagasse, coconut and bamboo fibers are some of the natural fibers that have attracted attention for the preparation of composite materials because of their low cost compared with synthetics fibers (glass, carbon). The performance of a natural fiber as reinforcement in composite materials is linked to its ability in term of adhesion with the synthetic matrix. This depends mainly on the quality of the fiber surface. In order to improve this adhesion, a thin reactive coating is generally used. In this study, cold He plasma treatments have been carried out on reinforcing flax fiber. Composites with unsaturated polyester resin (UPR) have been used with untreated flax fibers and plasma-treated fibers. The data characterizing the thermal, mechanical (dynamic and static) will be presented in order to analyze the efficiency of the He plasma treatment on the composite performances.     

Correlation of the mechanical properties to the fiber–matrix adhesion of Nextel 312™ fiber/BN/Blackglas™ composites

Boron nitride (BN)-coated aluminoborosilicate (Nextel? 312) fibers, produced via ammonia nitridation, along with 'as-received' and 'desized' fibers, were composited in a silicon oxycarbide (Blackglas?) matrix. The mechanical properties, failure properties, and fiber–matrix interfacial chemistry of the composite were investigated. BN treated fiber composites show a 90% improvement in flexural strength and substantial increases in shear strength (short beam shear and Iosipescu) over the 'as-received' fiber composite. The composite fabricated with 'desized' fibers underwent spontaneous delamination during pyrolization, precluding mechanical testing. X-ray photoelectron spectroscopy of the starting materials and of composite fracture surfaces combined with scanning electron microscopy and energy dispersive X-ray spectroscopy indicate that the locus of failure of the BN-coated fiber composite occurs at the matrix/BN coating interface.     

Imaging surface electronic structure of NiAl(110) using low-temperature scanning tunneling microscopy

The surface electronic structure of NiAl(110) is examined by means of scanning tunneling microscopy and spectroscopy at a temperature of 4 K. Topography and conductance images for a wide range of bias voltages reveal wavelike patterns around steps and defects. Fourier transforms of conductance images are used to map the surface electronic structure of NiAl(110). We interpret the patterns in the Fourier transforms in terms of surface resonances, and analyze the details of its dispersion relation E(k_). A comparison with density-functional-based calculations and photoemission experiments is presented, and alternative explanations for the appearance of structures in Fourier transforms of conductance images are discussed.     

Studying the Degradation of Reinforced Composites by High-Resolution Ultrasonic Means

Nondestructive means of pulsed acoustic microscopy are used to visualize and assess the bulk microstructure of carbon fiber reinforced composites. Irreversible changes in the composite structure under the influence of external mechanical and climatic factors are studied, and the dynamics of the accumulation and growth of microscopic defects leading to destruction is studied. Ultrasonic explorations are conducted at frequencies of 50–100 MHz. It is shown that scattered (diffracted) radiation participates in image formation; this makes it possible to detect small cavities (detachment of reinforcing fibers), clusters of microscopic defects, and inclined extended cracks oriented along the fibers’ packing. These cracks are precursors to the brittle fracture of a composite, and their visualization is difficult with standard ultrasonic methods.     

小波图像融合在太赫兹无损检测中的应用

玻璃纤维增强复合材料被广泛应用于航天、航空及其他军民各领域,它在制备和使用过程中通常会出现多个缺陷。太赫兹时域光谱成像技术有望成为玻璃纤维增强复合材料无损检测的有力补充手段。在太赫兹时域光谱成像过程中,可以选取时域或频域波形中的不同参数来进行成像。对于不同的缺陷,能够有效地对其进行检测的参数是不一样的。采用基于小波分解的图像融合方法将多幅不同参数获取的太赫兹反射图像结合起来,得到一幅包含所有缺陷信息的新图像。研究表明,基于小波分解的图像融合方法在太赫兹无损检测中的应用,能够获取单一参数成像无法检测的缺陷信息,为复合材料太赫兹图像后期处理提供了新的技术方法。     

Effect of chemical modifications of the pineapple leaf fiber surfaces on the interfacial and mechanical properties of laminated biocomposites

Natural fiber reinforced renewable resource based laminated composites were prepared from biodegradable poly(lactic acid) (PLA) and untreated or surface-treated pineapple leaf fibers (PALF) by compression molding using the film stacking method. The objective of this study was to determine the effects of surface treatment of PALF on the performance of the fiber-reinforced composites. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to aid in the analysis. The mechanical properties of the PLA laminated composites were improved significantly after chemical treatment. It was found that both silane- and alkali-treated fiber reinforced composites offered superior mechanical properties compared to untreated fiber reinforced composites. The effects of temperature on the viscoelastic properties of composites were studied by dynamic mechanical analysis (DMA). From the DMA results, incorporation of the PALF fibers resulted in a considerable increase of the storage modulus (stiffness) values. The heat defection temperature (HDT) of the PALF fiber reinforced PLA laminated composites was significantly higher than the HDT of the neat PLA resin. The differential scanning calorimeter (DSC) results suggest that surface treatment of PALF affects the crystallization properties of the PLA matrix. Additionally, scanning electron microscopy (SEM) was used to investigate the distribution of PLA within the fiber network. SEM photographs of fiber surface and fracture surfaces of composites clearly indicated the extent of fiber–matrix interface adhesion. It was found that the interfacial properties between the reinforcing PALF fibers and the surrounding matrix of the laminated composite are very important to the performance of the composite materials and PALF fibers are good candidates for the reinforcement fiber of high performance laminated biodegradable biocomposites.     

Electrostatic micromachine scanning mirror for optical coherence tomography

Compact electrostatic micromirror structures for use in the scanning arm of an optical coherence tomography (OCT) system are described. These devices consist of millimeter-scale mirrors resting upon micrometer-scale polyimide hinges that are tilted by a linear micromachine actuator, the integrated force array (IFA). The IFA is a network of deformable capacitor cells that electrostatically contract with an applied voltage. The support structures, hinges, and actuators are fabricated by photolithography from polyimide-upon-silicon wafers. These devices were inserted into the scanning arm of an experimental OCT imaging system to produce in vitro and in vivo images at frame rates of 4 to 8 Hz.