Invisible Defects Research Articles

Imaging of Local Stiffness of Damaged Polycrystalline Copper: Nondestructive Evaluation by Resonance Ultrasound Microscopy

The distribution of the local stiffness of a polycrystalline copper exposed to a creep test was studied by resonance ultrasound microscopy. The local effective modulus was evaluated from the resonance frequency of the isolated langasite oscillator touching the specimen. Defects appeared predominantly on grain boundaries, and they were clearly visualized by the stiffness microscopy through the significant decrease of the effective stiffness. The stiffness within the grains becomes lower regardless of invisible defects. The stiffness distribution was quantitatively analyzed by the contact model between two anisotropic bodies and by the micromechanics modeling. The microscopic stiffness shows much higher sensitivity to the defects than the macroscopic stiffness.

Seismic diagnosis of railway substructures by using secondary acoustic emission

One difficult task for the seismic diagnosis of existing structures is how to nondestructively evaluate the damage degree of invisible substructures, such as embedded foundations. To diagnose substructures efficiently, a method for nondestructive inspection is developed by applying acoustic emission (AE) technique. As a newly proposed method, characteristics of secondary AE induced by train operations were investigated, and experiments using model piles and in-situ AE monitoring of in-service railway bridges conducted under railroad traffic, from which it was demonstrated that the proposed method is practicable enough to detect invisible defects in structures. A new index, known as RTRI (ratio of Repeated Train load at the onset of AE activity to Relative maximum load for Inspection period) is proposed for structural damage qualification based on the results of in-situ AE monitoring.

Application of the magneto-optic Faraday effect in NDT

A magneto-optic/eddy current imaging device is presented in this paper to detect invisible defects on the surface and at the subsurface of metallic specimens. The device combines a magnetic inductor to induce eddy currents in the structure under test with an optical set-up to image the resultant magnetic field, thanks to the magneto-optic Faraday effect occurring in a magnetic-optic film which the linear polarised light penetrates. Finally, the image is received by Charge Coupled Device (CCD) to realise visual non-destructive testing. In this paper, the operation principle and the set-up of the new system are described, and the experimental results are discussed, according to which the method presented is proved feasible to non-destructive testing.

The Yield Enhancement Methodology for Invisible Defects Using the MTS+ Method

Whenever we try to enhance the production yield, we have problems identifying the cause of invisible defects over the entire process, even more so for charge-coupled devices (CCD). This time, we utilized the Mahalanobis Taguchi System (MTS) method with several original techniques to identify the cause of failure in the wafer process. We calculated the historical data of CCDs process parameter and took several countermeasures. According to the results, we learned that the invisible defects corresponded to the contamination of organic matter and the front-end process's sensitivity.

Non-destructive evaluation of brazed joints between cooling tube and heat sink by IR thermography and its verification using FE analysis

A non-destructive testing (NDT) and evaluation technique for the assessment of defects in brazed joints is presented in this paper. It is based on the analysis of infrared thermography (IRT) images, which produces two-dimensional temperature fingerprints to qualitatively see the invisible defects. This feature is fruitfully exploited to detect the significant faults in the brazed joints between the cooling tube and heat sink of the plasma facing components (PFC). Three-dimensional finite element (FE) analyses have been performed to simulate the brazing defects. Additional investigations like non-destructive radiographic test also confirms the experimental observations obtained from IRT.

Tampon Inspection Unit – Automation and Image Processing Application in an Industrial Production Process

Customers expect defect-free goods from the manufacturer. Both visible and invisible defects can result in expensive complaints, even if the function of the product is not affected. In many production processes, however, visual inspection is the only step that is still performed manually, which is very time-consuming and often only carried out on a spot check basis. In most cases it would be far more profitable to use machine vision to perform this task automatically. This paper describes a unique tampon inspection system for inline quality control based on image processing. In addition to detailed information about the hardware and software components, the paper also gives an outlook on future optimisation steps.

Damage evaluation of railway structures by using train-induced AE

For efficient maintenance of railway structures, nondestructive inspection for bridge substructures is developed by applying acoustic emission (AE) technique. As a newly proposed method, characteristics of secondary AE induced by a train in service are investigated. Based on AE experiments with model piles, in situ AE monitoring of railway bridges are conducted under railroad traffic. It is demonstrated that the proposed method is practical enough to detect the invisible defects in railway structures. Furthermore, a new index named RTRI (ratio of Repeated Train load at the onset of AE activity to Relative maximum load for Inspection period) is proposed for the evaluation of structural integrity. It is confirmed that RTRI is effective for in situ AE monitoring.

Damage evaluation of railway structures by using train-induced AE

For efficient maintenance of railway structures, nondestructive inspection for bridge substructures is developed by applying acoustic emission (AE) technique. As a newly proposed method, characteristics of secondary AE induced by a train in service are investigated. Based on AE experiments with model piles, in situ AE monitoring of railway bridges are conducted under railroad traffic. It is demonstrated that the proposed method is practical enough to detect the invisible defects in railway structures. Furthermore, a new index named RTRI (ratio of Repeated Train load at the onset of AE activity to Relative maximum load for Inspection period) is proposed for the evaluation of structural integrity. It is confirmed that RTRI is effective for in situ AE monitoring.

Secondary AE Techniques for Non-Destructive Inspection of Railway Structures

In this paper, the authors propose the use of acoustic emission (AE) techniques for the efficient maintenance of railway structures. They investigate the characteristics of secondary AE induced by train loading and describe how experiments were conducted using model piles and in-situ AE monitoring of in-service railway bridges. Results show that the proposed method is suitable enough for detecting invisible defects. Based on the results of the in-situ AE monitoring, the authors propose a new index known as RTRI (the ratio of Repeated Train load at the onset of AE activity to Relative maximum load for Inspection period).

Dynamic properties of injection-moulded nickel-carbon low alloy steel

The mechanical property change and defect structures were investigated on Fe-Cr and Fe-Mn alloys irradiated in the JMTR and the FFTF. Dislocation loop density increases much larger with manganese levels than chromium levels in irradiation in the JMTR, while in the FFTF, dislocation density of the Fe-Cr alloys is much larger than in the Fe-Mn alloys. This reverse trend is due to the saturation in the development of dislocation loops. The Fe-0.1 and 0.4% Cr with dislocation density much lower than that of 2% Cr, and that of the Fe-0.1 and 0.4% Mn much lower than that of 2% Mn showed the increment in yield strength almost the same as that of the Fe-2% Cr and rather larger than that of the Fe-2% Mn, respectively, in the JMTR. Yield strength increase without significant variation in strain hardening exponent is observed in the Fe-0.1% Cr and Fe-0.1% Mn irradiated in the FFTF and very small voids are observed in the Fe-0.1% Mn irradiated in the JMTR. These results suggest the existence of invisible defect clusters produced by irradiation.

Radio-frequency antenna studies for high-current, high-duty-cycle, H− volume sources (abstract)

The Spallation Neutron Source requires an ion source capable of delivering a high-current (∼50 mA) H− beam with a 6% duty cycle continuously for the three weeks between the scheduled maintenance periods. The cesium-enhanced, multicusp volume ion source under development on the integrated test facility at LBNL delivers H− ion currents up to 50 mA, increasing approximately linearly with the rf power. Initial experience using porcelain-coated copper antennas, however, indicates lifetimes will fall below the desired three-week period, mostly limited by antenna failures. In an effort to improve our understanding of the antenna limitations, we are in the process of developing an antenna test dome, which will allow us to visually observe and study the rf-initiated discharge at low-power levels. We hope to be able to test antennas for invisible defects by observing and measuring the onset of the discharge. In addition, we are planning to test different antennas. Results will be presented at the meeting.

Electron Beam Welding of Zr-Based Bulk Metallic Glass to Crystalline Zr Metal

We have tried an electron-beam welding of a Zr-based bulk metallic glass plate to a polycrystalline Zr metal one for a Zr41Ti14Cu12Ni10Be23 (at%) bulk metallic glass having an excellent glass forming ability. We have succeeded in butt-welding the bulk metallic glass and pure Zr metal plates with a thickness of 3 mm. Invisible defect or clack was detected around the bead and heat-affected zone. The bulk metallic glass around the interface kept the amorphous state. Formation of any crystalline phases except for hcp-Zr was not detected in the interface. The interface of the successfully welded sample exhibited enough toughness and joining strength to endure the bending through 90 degrees by hammering.

Diagnostic of the conservation state of antique Italian paintings on panel carried out at the Laboratorio di Restauro dell'Opificio delle Pietre Dure in Florence, Italy with ESPI-based portable instrumentation

The aim of this work was to use non-destructive optical measurement techniques to assess the conservation state of ancient Italian paintings and to experiment outside of the laboratory with the most recent ESPI (electronic speckle pattern interferometry) portable instruments developed within the Photonic Technologies and Diagnostic Laboratory of the European Commission Joint Research Centre of Ispra, Italy. The measurements described here took place at the Laboratori di Restauro dei Dipinti dell'Opificio delle Pietre Dure in Florence, Italy. The technique detects hardly visible and invisible defects on paintings on panel during the restoration phase and allowed the production of both qualitative and quantitative data, owing to its high resolution and sensitivity to thermal deformation. The system used allowed the inspection of a larger area (400×300 mm) in comparison to that reported in literature concerning continuous wave portable ESPI systems applied in the conservation field.

Detection of the nearly invisible defect that disrupts bulk superconductivity inPr1.5Ce0.5Sr2Cu2NbO10

Detection of the nearly invisible defect that disrupts bulk superconductivity in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Pr</mml:mi></mml:mrow><mml:mrow><mml:mn>1.5</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ce</mml:mi></mml:mrow><mml:mrow><mml:mn>0.5</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Sr</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">NbO</mml:mi></mml:mrow><mml:mrow><mml:mn>10</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

815 赤外線非破壊診断基準の確立へ向けた数値シミュレーション

Infrared thermography is one of the most attractive techniques for diagnosing various invisible defects included in objects or bodies, because a two-dimensional field of testing targets can be evaluated nondestructively and instantaneously. In this paper, three-dimensional numerical simulation of thermal conduction is performed for the nondestructive diagnosis using infrared rays to confirm the applicability and to establish the diagnostic standard. It is revealed from a series of numerical simulation and image processing that the infrared thermography is useful in diagnosing invisible defects.

Invisible and visible point defect clusters in neutron irradiated iron

Microstructure evolution in a low-dose neutron-irradiated iron was examined with a transmission electron microscope (TEM). The characteristics of the temperature dependence of defect structures in irradiated iron were as follows, (a) rather lower number density of defect clusters at 473 K than at 573 K, (b) development of dislocation loops and voids at an intermediate temperature of 623 K and (c) formation of irregularly shaped dislocation loops at 673 K. Comparing the defect structures produced by the irradiation with a conventional temperature control and that with an improved temperature control, nucleation of defect clusters was suppressed under neutron irradiation at 473 K. From the defect structures introduced by irradiations in which the irradiation temperature was cyclically changed between two temperatures (T-cycle irradiation), the accumulation of a large number of invisible vacancy type defect clusters by irradiation at 473 K was strongly suggested.

Defect structure development in a pure iron and dilute iron alloys irradiated with neutrons and electrons

The defect structure and mechanical property changes were observed for pure iron of 99.99% purity and a series of Fe–(0.1% and 0.4%) Cr and Fe–(0.1% and 0.4%) Mn dilute alloys irradiated with neutrons. From the comparison of the defect structures with yield strength change, a large contribution of the invisible defect clusters to the irradiation hardening was expected in the specimens irradiated in Japan Materials Test Reactor (JMTR), whereas these clusters are not found after irradiation in the Fast Flux Test Facility (FFTF). The electron irradiation experiments showed that addition of chromium and manganese to 0.1% in pure iron, development of large dislocation loops is suppressed, and frequent nucleation of small loops at the early stage of the electron irradiation is observed, similar to that in ultra-high purity iron of 99.9999% purity. The mechanisms of dislocation loop development in the early stage of irradiation for Fe–Cr and Fe–Mn are considered to be different.

On the NDT and E for the diagnosis of defects using infrared thermography

The increasingly recognized applicability of infrared thermography has caused developments of remote-sensing diagnoses for various engineering applications. A significant advantage of this technique is that we can diagnose invisible defects nondestructively and safely. For maintaining and managing various structures satisfactorily, it is very important to detect many kinds of invisible defects such as separation, cavity, inclusion and so on. Although the infrared thermography for NDT and E has therefore been examined extensively, few fundamental investigations have addressed the numerical computation to evaluate the detection mechanism and the quantitative limit under various conditions. It is important to discuss them theoretically with the aid of the appropriate numerical computation. In this paper, therefore, we certify them using a series of fundamental numerical computation with the aid of the concerned experimental investigation using the infrared thermography. From the numerical and experimental investigations, the effects of defect's depth and size on the detection are elucidated. In addition to the fact, it is obvious that the applicability of the present NDT and E depends on a heating condition and a relative difference of thermophysical property between the defect and its surrounding.

Investigation and control of domain formation in ferroelectric liquid crystal devices

This paper explores the causes of domain nucleation and investigates methods to control the location and threshold of defect sites. By observing the reappearance of invisible defect sites after full annealing it was determined that intrinsic surface features are able to seed nucleation. Intentional modification of the surface topology was investigated and found to have a dramatic influence on domain nucleation and growth. Some applications that might benefit from this direct control over domain nucleation are discussed.

非破壊検査における可視化 見えない傷を診る 非破壊検査と可視化

非破壊検査における可視化 見えない傷を診る 非破壊検査と可視化