A New Instrument for the Detection of Fatigue Cracks under Airframe Rivets

During the past several years the electromagnetics laboratory at NASA Langley Research Center has focused on the Aging Aircraft Program. A major goal of this program has been the development of easy to use yet highly accurate inspection methods for the detection of flaws in airframe fuselage structures. A major breakthrough in this research came with the discovery of the Self-Nulling Probe Effect in November of 1992 [1]. It was clear that the unambiguous flaw signature of the probe could be developed into a low cost and easy to use fatigue crack detection device. Work toward this goal proceeded quickly, and a prototype hand held crack detector was introduced by mid 1993 [2]. As research into the precise flaw detection mechanism of the probe began to provide a deeper insight into the device [3–4], more sophisticated uses of the probe were conceived [5–6]. In particular, the Rotating Probe Method for the Detection of Fatigue Cracks under Airframe Rivets was beginning to be developed and tested by the end of 1993 [6], less than 1 year after the original discovery of the Self-Nulling Probe Effect

Application of Self-Nulling Eddy Current Probe and Spin-Off Sensor Technologies to Airline Industries and Beyond

As the existing commercial air fleet of the airline industry ages, the major demand on the NDE community is to develop simple, cost effective methodologies of higher detectability and reliability. To satisfy such a demand a focused R&D effort has been performed for the past several years through NASA Airframe Structural Integrity Program (NASIP). This particular program concentrates on the development of methodologies applicable to NDI of aircraft fuselage, which, being a thin metallic structure, is best suited for inspection by various electromagnetic techniques. Such is the direct motivation for the development of the self-nulling eddy current probe technology.</p

Characteristics of Frequency Domain Spectrum of Self-Nulling Eddy Current Probe Output

Since its introduction several years ago, the self-nulling eddy current probe [1–3] technology has been one of the focal points of the aging aircraft related R&D effort. Numerous application areas have broadened the scope of the probe which has also helped in better understanding the underlying principle. As the technology matures, however, deeper understanding on the various details related to the self nulling effect is needed to overcome difficulties associated with the current field tests and expand its application areas. A particular problem to be addressed is in differentiating the effect of small, shallow surface cracks from that of probe wobble during automated data acquisition operation

A New ECT Probe with Rotating Direction Eddy Current

In the eddy current testing, various kinds of noise are generated by variations of many factors such as the probe lift-off and the material configuration. A lot of efforts have been made to develop new probes with little noise[1,2]. The authors think that it is necessary to develop a new noise free ECT probe in order to conduct the quantitative nondestructive testing.</p

Imaging Flaws in Thin Metal Plates Using a Magneto-Optic Device

The ability to quickly detect flaws in thin aluminum alloy sheets is of critical importance to the commercial airline fleets. Current eddy-current methods, although very effective at exposing flawed regions, can be very time consuming when applied to airframe structures. The need for a fast, effective means of detecting critical flaws needs to be met. The purpose of this paper is to present preliminary results describing some capabilities of a new instrument, The Magneto-Optic/Eddy Current Imager, as an NDE tool for use in the Airframe Structural Integrity Program

Performance Management and Stakeholder Groups In Selected Asian Countries

Eddy current techniques are widely used to measure the thickness of electrically conducting materials[1–3]. The approach, however, requires an extensive set of calibration standards and can be quite time consuming to set up and perform. Recently, an electromagnetic sensor was developed which eliminates the need for impedance measurements [4–8]. The ability to monitor the magnitude of a voltage output independent of the phase enables the use of extremely simple instrumentation. Using this new sensor a portable hand-held instrument was developed (Fig. 1). The device makes single point measurements of the thickness of nonferromagnetic conductive materials. The technique utilized by this instrument requires calibration with two samples of known thicknesses that are representative of the upper and lower thickness values to be measured. The accuracy of the instrument depends upon the calibration range, with a larger range giving a larger error. The measured thicknesses are typically within 2–3% of the calibration range (the difference between the thin and thick sample) of their actual values. In this paper the design, operational and performance characteristics of the instrument along with a detailed description of the thickness gauging algorithm used in the device are presented

LPS-induced up-regulation of TGF-β receptor 1 is associated with TNF-α expression in human monocyte-derived macrophages

The immunosuppressive activity of TGF-β-mediated signaling is well documented, but in contrast, its ability to promote proinflammatory responses is less clear. In this study, we report that blockade of TGF-β signaling by a specific inhibitor of the TGF-β receptor I [activin receptor-like kinase 5 (ALK5)] SB431542 significantly reduces the production of TNF-α, a key proinflammatory cytokine, by LPS-stimulated human monocyte-derived macrophages. ALK5 protein was only detectable after LPS stimulation, and the failure of treatment with SB431542 to alter TNF-α mRNA expression indicates that regulation is post-transcriptional. The additive effect of blocking TGF-β and p38 MAPK signaling on reducing TNF-α but not IL-6 production suggests that there is selectivity in pathway signaling. SB431542 had similar inhibitory effects on TNF-α production by human monocytes and endothelial cells as well as macrophages. Furthermore, treatment with SB431542 reduced plasma TNF-α levels and tissue damage and thereby, prevented the lethal effects of LPS in a mouse model of septic shock. Our data demonstrate a direct effect of TGF-β signaling via ALK5 on the regulation of TNF-α synthesis. © Society for Leukocyte Biology.link_to_subscribed_fulltex

The effect of ytterbium fluoride and barium sulphate nanoparticles on the reactivity and strength of a glass-ionomer cement

Objectives: While clinical advantages of glass-ionomers include fluoride release and radiopacity, disadvantages include low strength, slow initial setting times and opacity. The addition of nanoparticles, in particular those containing fluoride and cross-linkable ions, may mitigate the disadvantages while further improving the advantages. This investigation evaluated the effects of the addition of ytterbium fluoride (YbF3) and barium sulphate (BaSO4) on the strength and reactivity of a commercial glass-ionomer cement. Methods: YbF3 and BaSO4 nanoparticles were incorporated into the powder component of Riva SC (SDI Ltd., Bayswater, Australia) at 1, 2, 5, 10, 15, and 25% by weight. Capsules were assembled at a powder:liquid ratio of 2.9:1, activated and mixed, and the resultant pastes evaluated for working time, initial setting time, 24-h surface hardness and 24-h compressive strength. Results: Working and initial setting times were reduced with the addition of YbF3. Addition of BaSO4 at low concentrations reduced working and initial setting times, but further addition delayed the setting reaction. Compressive strength decreased with the addition of either YbF3 or BaSO4, while surface hardness was slightly but insignificantly higher at 1-2% nanoparticles and then decreased with increasing nanoparticle concentrations. Significance: Nanoparticles modified the setting characteristics, strength and surface hardness of a commercial glass-ionomer cement, and may be useful for refining the handling characteristics of these materials. Further improvements in powder blending may result in more significant improvements in mechanical properties. © 2005 Academy of Dental Materials.link_to_subscribed_fulltex

Magneto-Optic Image Classification Using Neural Networks

The aging aircraft program sponsored by the FAA is keen on improving existing technologies and developing new techniques for the detection of cracks and corrosion in aircraft structures. This program is a part of the overall scheme of addressing the global aging infrastructure problem. The authors have been involved in the aging aircraft program through the NASA Langley Research Center (LaRC).</p

Quality Factor And Microslipping Of Fatigue Cracks In Thin Plates At Resonant Vibration

Resonant vibrations have been stimulated in thin metal plates using a non-contacting electromagnetic driver. A sinusoidal force was applied in a swept frequency fashion and the resulting surface displacements were monitored through the use of an acoustic microphone. It has been found that the presence of a fatigue crack in the sample causes a broadening of the second resonance peak. The Q factors of the resonance curves were determined and are directly correlated with the presence of fatigue cracks in the samples. The broadening of the curves is explained in terms of a microslipping at the crack face walls which reduces the amplitude of the resonant vibration by increasing the damping of the system. A comparison is made between the resonance characteristics of fatigue damaged and notched samples, where the stiffness of the two systems is nearly constant while the interaction between crack face walls is eliminated in the latter. INTRODUCTION It has previously been shown that resonant mo..