Thin Metallic Structures Research Articles

램파와 압전소자 극성을 사용한 강구조의 실시간 균열손상 감지기법 개발

이 연구에서는 강교량과 같은 토목 구조물에서 유도파의(Guided waves)한 종류인 램파(Lamb wave)를 이용하여 실시간으로 균열손상을 감지할 수 있는 새로운 비파괴 검사방법을 제안한다. 기존의 유도파를 이용한 기술들은, 손상을 감지하기 위해 비손상 상태의 자료를 저장하고 이를 새로이 얻어진 결과와 비교하는 방법을 사용함으로써 잠재적인 손상을 진단해 왔다. 그러나, 공용중인 강구조물은 다양한 하중 뿐 아니라 상시로 변화하는 자연환경에 노출되어 있기 때문에 동일한 비손상 상태의 응답을 얻는 것이 매우 어려우며 이러한 방법을 적용할 경우 오보(false alarm)의 우려도 매우 높다고 할 수 있다. 따라서 이 연구에서는 보다 안정적인 손상감지기법을 개발하기 위해 기존에 얻어진 초기치를 이용하지 않으면서 실시간으로 손상 여부를 판단할 수 있는 방법을 제안하고자 한다. 이 연구에서 제안된 감지 기술은, 압전소자의 극성과 판파의 특성을 이용하는 것으로 얇은 판의 양면에 부착된 압전소자를 통하여 균열손상에 의한 신호를 선택적으로 감지해 내는 데에 그 목적이 있다. 균열이 발생한 판에서 진행하는 판파는 균열로 인한 판의 두께변화로 인해 모드 변화를 일으키게 되는데, 제안된 감지기법으로 이러한 모드 변화만을 선택적으로 추출할 수 있다. 다양한 수치해석과 실험을 통해 이 연구에서 제안된 손상감지기법의 효율성과 적용성을 입증한다. A new methodology of guided wave based nondestructive testing (NDT) is developed to detect crack damage in civil infrastructures such as steel bridges without using prior baseline data. In conventional guided wave based techniques, damage is often identified by comparing the "current" data obtained from a potentially damaged condition of a structure with the "past" baseline data collected at the pristine condition of the structure. However, it has been reported that this type of pattern comparison with the baseline data can lead to increased false alarms due to its susceptibility to varying operational and environmental conditions of the structure. To develop a more robust damage diagnosis technique, a new concept of NDT is conceived so that cracks can be detected without direct comparison with previously obtained baseline data. The proposed NDT technique utilizes the polarization characteristics of the piezoelectric wafers attached on the both sides of the thin metal structure. Crack formation creates Lamb wave mode conversion due to a sudden change in the thickness of the structure. Then, the proposed technique instantly detects the appearance of the crack by extracting this mode conversion from the measured Lamb waves even at the presence of changing operational and environmental conditions. Numerical and experimental results are presented to demonstrate the applicability of the proposed technique to crack detection.

Fast three-dimensional nanostructure fabrication by laser-assisted nanotransfer printing

The authors present a laser-assisted nanotransfer printing technique for transferring metal nanopatterns onto prepatterned substrates. A fused quartz mold covered with an array of chromium nanodots is pressed against the surface of a photolithographically patterned substrate, while a single laser pulse from a quadrupled-frequency solid state Nd:YAG laser is used to melt the thin metal structures. By controlling the laser fluence, selective metal pattern transfer can be realized only on the protruded area of the substrate upon separation of the quartz support. The transferred chromium nanodots are then used as an etch mask to pattern three-dimensional structures.

Copper-Airbridged Low-Noise GaAs PHEMT With$hboxTi/hboxWN_x/hboxTi$Diffusion Barrier for High-Frequency Applications

A GaAs pseudomorphic HEMT (PHEMT) with Cu-metallized interconnects was successfully developed. Sputtered WN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> was used as the diffusion barrier and Ti was used as the adhesion layer to improve the adhesion between WN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Cu interface in the thin-metal structure. After copper metallization, the PHEMTs were passivated with silicon nitride to avoid copper oxidation. The Cu-airbridged PHEMT showed the saturation I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> was 250 mA/mm and the g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> was 456 mS/mm. The Ti adhesion layer plays a significant role on the g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> uniformity of the Cu-metallized PHEMTs. The GaAs PHEMTs with Ti/WN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Ti/Cu multilayer have better noise figure and associated gain than those of the devices without the Ti adhesion layer. The fabricated Cu-metallized GaAs PHEMT with Ti/WN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Ti/Cu multilayer has a noise figure of 0.76 dB and an associated gain of 8.8 dB at 16 GHz. The cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) is 70 GHz when biased at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> =1.5V. These results show that the Ti/WN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Ti multilayer can serve as a good diffusion barrier for Cu metallization process of airbridge interconnects on GaAs lownoise PHEMTs

Magnetization-Induced Third-Harmonic Generation in Nanostructures and Thin Films

This paper reports on the results of research into low-dimensional magnetic structures that have been intensively studied over previous decades due to the discovery of novel effects that are exhibited by these structures but not observed in bulk magnetic materials. A nonlinear optical analog of the magnetooptical Kerr effect is revealed in the optical third-harmonic generation in thin magnetic metallic films and nanogranular structures. It is shown that the magnetic nonlinear optical Kerr effect observed in the third harmonic exceeds the magnetooptical analog by more than one order of magnitude. © 2005 Pleiades Publishing, Inc.

Einheitliches Versagenskriterium - Zur Definition des Versagenskriteriums für Zeitfestigkeitsversuche an gefügten Dünnblechen

In fatigue tests performed within the fatigue endurance limit, the lifetime of specimens is determined by the definition of the failure criterion. For investigations on joined thin sheet metals, different failure criteria have as yet been applied which not only lead to a restricted comparability of the test results, but also to different statements on the fatigue behaviour of joints. This contribution presents a discussion of the advantages and drawbacks of various definitions used in practice for determining the specimen failure. It is intended to start a debate in which a consistent, comparable failure criterion should be established. This criterion should then be applied by all users in industry and research in order to obtain comparable results from fatigue tests on joined thin sheet metal structures in the future.

Observations of reaction zones at chromium/oxide glass interfaces

Cr is often used in thin metallic film structures on oxide glasses since it exhibits good adhesion. The most likely explanation of the basic adhesion mechanism is the formation of a graded metal oxide layer at the interface. In general, details of the interface properties are needed to get a complete understanding of phenomena such as adhesion. We report here observations of interface structures using spatially resolved electron energy loss spectrometry with a small probe (2 Å) scanning transmission electron microscope. Two interfaces, evaporated Cr/alkaline earth boroaluminosilicate glass and sputtered Cr/barium boroaluminosilicate glass, are examined. As expected from the classical adhesion theory, very thin partially oxidized intermediate layers are seen in both samples. However, a 5 nm Cr diffusion layer is also found in the evaporated Cr/glass system (without heat treatment), but it appears absent in the sputtered Cr glass system (with heat treatment). This difference suggests that the mechanisms of the adhesion of Cr to oxide glass are dependent on interface history.

Finite element analysis of shot peening

Abstract The shot peening process is largely used for the surface treatment of metallic components with the aim of increasing surface toughness and extending fatigue life. A secondary consequence of the process is that the residual stress distribution developed within the material may induce distortion of the component. This effect may therefore be used constructively in the straightening and forming of thin flexible metallic structures. In this paper, the various techniques available for modelling the effect of peening with finite elements are discussed. In particular, a method of simulating the effect of peening on large flexible panels is presented. Analyses are shown in which a novel loading is applied to finite element meshes in order to produce the desired residual stress distribution. Results from tests are compared to finite element analyses and preliminary results of large scale analyses are presented.

Patterning of Cu, Co, Fe, and Ag for magnetic nanostructures

Wet and dry etching of thin metallic multilayer structures is necessary for the development of sensitive magnetic field sensors and memory devices based on spin–valve giant magnetoresistance elements. While it is well established that Cu, Co, and Fe are soluble in HNO3 and H3PO4 at room temperature, little effort has been made to investigate selective wet and dry etch chemistries. For example, we find Ag is not etched in H2SO4, HCl, or H3PO4 under conditions where etch rates for the other metals are in the range of 2000–60 000 Å/min. Electron cyclotron resonance (ECR) SF6/Ar plasmas provide etch selectivities of ⩾5:1 for Ag over Cu, Co, and Fe, while lower selectivities are obtained with CH4/H2/Ar. Cl2-based plasma chemistries leave significant metal–chlorine surface residues, which can be removed in situ by low ion energy H2 or Ar plasma treatments that eliminate corrosion problems. Cu etch rates in excess of 3000 Å/min at 25 °C can be obtained in ECR Cl2/Ar discharges because the high ion flux prevents formation of a CuClX-rich selvedge layer, which normally only is volatile for etch temperatures ⩾220 °C in conventional reactive ion etch systems. Photoresist masks suffer severe reticulation under ECR conditions, at least for microwave powers &amp;gt;400 W, and SiO2 or SiNX thin films offer much better etch resistance.

Biopsy needle susceptibility artifacts.

Understanding the appearance of thin metallic structures in magnetic resonance imaging is important for evaluating the potential role of MRI in guiding and monitoring percutaneous interventions. As most MR compatible instruments are made from materials with a susceptibility different from water, their visibility is enhanced beyond what is expected on the grounds of displaced water alone. Unfortunately, this artifactually enhanced visibility is not constant, but instead depends on a variety of factors. This article presents computer simulations of the image distortion resulting from magnetic susceptibility differences between a needle and the surrounding tissue. The simulations show not only an artifact size that is dependent on needle composition, orientation, and pulse sequence, but also a corresponding shift of the artifact center away from the actual center of the needle. These effects place limits on the accuracy of MRI-guided needle tip placement.

Structure of PbxSn1−xTe films r.f. sputtered onto thin metallic structures

Structure of PbxSn1−xTe films r.f. sputtered onto thin metallic structures