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Aouni A. Lakis - One of the best experts on this subject based on the ideXlab platform.

  • Application of time–frequency analysis for automatic hidden corrosion detection in a multilayer Aluminum Structure using pulsed eddy current
    NDT & E International, 2012
    Co-Authors: Saleh Hosseini, Aouni A. Lakis
    Abstract:

    Abstract Pulsed eddy current (PEC) is a non-destructive testing method used to detect corrosion and cracks in multilayer Aluminum Structures which are typically found in aircraft applications. Corrosion and metal loss in thin multi-layer Structures are complex and variable phenomena that diminish the reliability of pulsed eddy current measurements. In this article, pulsed eddy current signals are processed to improve the accuracy and reliably of these measurements. PEC's results (time domain data) are converted by time–frequency analysis (Rihaczek distribution) to represent data in three dimensions. The time–frequency approach generates a large amount of data. Principal component analysis is applied as feature extraction to reduce redundant data to provide new features for classifiers. K -means clustering and expectation–maximization are applied to classify data and automatically determine corrosion distribution in each layer.

Saleh Hosseini - One of the best experts on this subject based on the ideXlab platform.

  • Application of time–frequency analysis for automatic hidden corrosion detection in a multilayer Aluminum Structure using pulsed eddy current
    NDT & E International, 2012
    Co-Authors: Saleh Hosseini, Aouni A. Lakis
    Abstract:

    Abstract Pulsed eddy current (PEC) is a non-destructive testing method used to detect corrosion and cracks in multilayer Aluminum Structures which are typically found in aircraft applications. Corrosion and metal loss in thin multi-layer Structures are complex and variable phenomena that diminish the reliability of pulsed eddy current measurements. In this article, pulsed eddy current signals are processed to improve the accuracy and reliably of these measurements. PEC's results (time domain data) are converted by time–frequency analysis (Rihaczek distribution) to represent data in three dimensions. The time–frequency approach generates a large amount of data. Principal component analysis is applied as feature extraction to reduce redundant data to provide new features for classifiers. K -means clustering and expectation–maximization are applied to classify data and automatically determine corrosion distribution in each layer.

Lucía Martínez-arcos - One of the best experts on this subject based on the ideXlab platform.

  • Durability of solar reflector materials for secondary concentrators used in CSP systems
    Solar Energy Materials and Solar Cells, 2014
    Co-Authors: Aránzazu Fernández-garcía, Maria Elena Cantos-soto, Christian Hutter, Christian Wieckert, Marc Röger, Lucía Martínez-arcos
    Abstract:

    Abstract Secondary concentrators are used in solar concentrating systems to redirect solar beams reflected by the primary concentrators to the focal point or line. These components allow to increase the concentrated solar flux density and hence to lower thermal radiation losses. Solar reflectors for secondary concentrators are permanently exposed to environmental conditions, high radiation fluxes and elevated temperatures that potentially cause stress and degradation throughout the time. Therefore, analyzing solar reflectors of secondary concentrators by simulating these conditions is crucial. No previous research works about the durability of solar reflector materials for secondary concentrators have been reported. The present work is focused on studying the degradation of the reflector materials by simulating accelerated aging, caused by several ambient parameters and the effect of concentrated radiation. Both cooled and uncooled systems for secondary concentrators are included in this study. According to results obtained, Aluminum reflectors and thin silvered-glass reflectors glued to an Aluminum Structure showed minimum reflectance losses and structural degradation under the operation conditions of cooled 3D secondary concentrators (tower systems). Following critical aspects to avoid reflector degradation were identified: to select a suitable adhesive material to glue the thin silvered-glass reflector to the support Aluminum Structure, to properly protect reflectors edges, to design a suitable cooling system and to avoid the combination of high radiation fluxes with mechanical stress. In addition, laminated silvered-glass reflectors have shown to be suitable for uncooled 2D secondary concentrators (Fresnel collectors). Furthermore, a comparison with naturally aged secondary concentrators using silvered-glass reflectors glued to an Aluminum Structure revealed that the simulated degradation under accelerated conditions performed in this work did reproduce the most frequent degradation patterns suffered in real operating conditions.

Minoru Sasaki - One of the best experts on this subject based on the ideXlab platform.

  • ^27Al MAS-NMR spectra of alumina aerogels
    Journal of Materials Research, 1993
    Co-Authors: Yasuyuki Mizushima, Makoto Hori, Minoru Sasaki
    Abstract:

    The ^27Al MAS-NMR spectra of alumina aerogels were determined. The spectra showed different profiles according to the supercritical methods used during drying. The alumina aerogel supercritically dried in a CO_2 extractor (80 °C, 15.7 MPa) displayed a pentahedral-coordinated Aluminum Structure. On the other hand, the alumina aerogel supercritically dried in an autoclave (270 °C, 26.5 MPa) revealed no pentahedral-coordinated Aluminum Structure. The absence of pentahedral-coordinated Aluminum was one factor for the lower temperature of transformation from the γ to the θ phase.

  • 27 Al MAS-NMR spectra of alumina aerogels
    Journal of Materials Research, 1993
    Co-Authors: Yasuyuki Mizushima, Makoto Hori, Minoru Sasaki
    Abstract:

    The 27 Al MAS-NMR spectra of alumina aerogels were determined. The spectra showed different profiles according to the supercritical methods used during drying. The alumina aerogel supercritically dried in a CO 2 extractor (80 °C, 15.7 MPa) displayed a pentahedral-coordinated Aluminum Structure. On the other hand, the alumina aerogel supercritically dried in an autoclave (270 °C, 26.5 MPa) revealed no pentahedral-coordinated Aluminum Structure. The absence of pentahedral-coordinated Aluminum was one factor for the lower temperature of transformation from the γ to the θ phase.

T. M. Olson - One of the best experts on this subject based on the ideXlab platform.

  • Carbon Nanotube Based Sensor to Monitor Crack Growth in Cracked Aluminum Structures Underneath Composite Patching
    Applied Composite Materials, 2015
    Co-Authors: T. M. Olson, Y. W. Kwon, D. C. Hart, D. C. Loup, E. A. Rasmussen
    Abstract:

    The paper investigates a carbon nanotube-based sensor to detect crack propagation in Aluminum Structures underneath composite patching. Initial tests are conducted to determine the correct procedure and materials to properly fabricate a carbon nanotube (CNT) based sensor, which is then placed in between a composite patch and the Aluminum Structure. The CNTs have been utilized as sensors in previous studies but only for sensing crack propagation within the composite itself. This study focuses on crack propagation in the base material and is not concerned with the composite. In this application, the composite is only a patch and can be replaced if damaged. The study conducts both tension and fatigue testing to determine the usefulness of the CNT sensor. The CNT sensor is shown to be effective in giving an indication of the crack propagation in the Aluminum. Correlation is done between the crack propagation length and the increase in electrical resistance in the CNT sensor under tensile and cyclic loading, respectively.

  • Development of Carbon Nanotube-Based Sensor to Monitor Crack Growth in Cracked Aluminum Structures Underneath Composite Patching
    2014
    Co-Authors: T. M. Olson
    Abstract:

    Abstract : This paper presents the design of a carbon nanotube-based sensor to detect crack propagation in Aluminum Structures underneath composite patching. Initial tests are utilized to determine the correct procedure and materials to properly fabricate a carbon nanotube (CNT) sensor, which is then placed in between a composite patch and the Aluminum Structure. CNTs have been utilized as sensors in previous studies but only for sensing crack propagation within the composite itself. This study focuses on crack propagation in the base material and is not concerned with the composite. In this application, the composite is only a patch and can be replaced if damaged. This study utilizes both tension and fatigue testing to determine the usefulness of the CNT sensor. The CNT sensor is shown to be effective in giving an indication of the crack propagation in the Aluminum. Correlation is done between the propagation length and the increase in resistance in the CNT sensor for tensile testing as the crack width is large enough to obtain an appreciable resistance change.