190 research outputs found
NASA Composite Materials Development: Lessons Learned and Future Challenges
Composite materials have emerged as the materials of choice for increasing the performance and reducing the weight and cost of military, general aviation, and transport aircraft and space launch vehicles. Major advancements have been made in the ability to design, fabricate, and analyze large complex aerospace structures. The recent efforts by Boeing and Airbus to incorporate composite into primary load carrying structures of large commercial transports and to certify the airworthiness of these structures is evidence of the significant advancements made in understanding and use of these materials in real world aircraft. NASA has been engaged in research on composites since the late 1960 s and has worked to address many development issues with these materials in an effort to ensure safety, improve performance, and improve affordability of air travel for the public good. This research has ranged from synthesis of advanced resin chemistries to development of mathematical analyses tools to reliably predict the response of built-up structures under combined load conditions. The lessons learned from this research are highlighted with specific examples to illustrate the problems encountered and solutions to these problems. Examples include specific technologies related to environmental effects, processing science, fabrication technologies, nondestructive inspection, damage tolerance, micromechanics, structural mechanics, and residual life prediction. The current state of the technology is reviewed and key issues requiring additional research identified. Also, grand challenges to be solved for expanded use of composites in aero structures are identified
Microwave NDT&E using open-ended waveguide probe for multilayered structures
Ph. D. Thesis.Microwave NDT&E has been proved to be suitable for inspecting of dielectric structures due
to low attenuation in dielectric materials and free-space. However, the microwave responses
from multilayered structures are complex as an interrogation of scattering electromagnetic
waves among the layers and defects. In many practical applications, electromagnetic analysis
based on analytic- and forward structural models cannot be generalised since the defect shape
and properties are usually unknown and hidden beneath the surface layer.
This research proposes the design and implementation of microwave NDT&E system for
inspection of multilayered structures. Standard microwave open-ended rectangular waveguides
in X, Ku and K bands (frequency range between 8-26.5 GHz) and vector network analyser
(VNA) generating sweep frequency of wideband monochromatic waves have been used to
obtain reflection coefficient responses over three types of challenging multilayered samples: (1)
corrosion progression under coating, (2) woven carbon fibre reinforced polymer (CFRP) with
impact damages, and (3) thermal coated glass fibre reinforced polymer (GFRP) pipe with inner
flat-bottom holes. The obtained data are analysed by the selected feature extraction method
extracting informative features and verify with the sample parameters (defect parameters). In
addition, visualisation methods are utilised to improve the presentation of the defects and
material structures resulting in a better interpretation for quantitative evaluation.
The contributions of this project are summarised as follows: (1) implementation of microwave
NDT&E scanning system using open-ended waveguide with the highest resolution of 0.1mm x
0.1 mm, based on the NDT applications for the three aforementioned samples; (2) corrosion
stages of steel corrosion under coating have been successfully characterised by the principal
component analysis (PCA) method; (3) A frequency selective based PCA feature has been used
to visualise the impact damage at different impact energies with elimination of woven texture
influences; (4) PCA and SAR (synthetic aperture radar) tomography together with time-offlight extraction, have been used for detection and quantitative evaluation of flat-bottom hole
defects (i.e., location, size and depth).
The results conclude that the proposed microwave NDT&E system can be used for detection
and evaluation of multilayered structures, which its major contributions are follows.
(1) The early stages (0-12month) of steel corrosion undercoating has been successfully
characterised by mean of spectral responses from microwave opened rectangular
waveguide probe and PCA.
(2) The detection of low energy impact damages on CFRP as low as 4 Joules has been
archived with microwave opened rectangular waveguide probe raster scan together with
SAR imaging and PCA for feature extraction methods.
(3) The inner flat-bottom holes beneath the thermal coated GFRP up to 11.5 mm depth has
been successfully quantitative evaluated by open-ended waveguide raster scan using
PCA and 3-D reconstruction based on SAR tomography techniques. The evaluation
includes location, sizing and depth.
Nevertheless, the major downside of feature quantities extracted from statistically based
methods such as PCA, is it intensely relies on the correlation of the input dataset, and thus
hardly link them with the physical parameters of the test sample, in particular, the complex
composite architectures. Therefore, there are still challenges of feature extraction and
quantitative evaluation to accurately determine the essential parameters from the samples. This
can be achieved by a future investigation of multiple features fusion and complementary
features.Ministry of Science and Technology of Royal Thai Government
and Office of Educational Affairs, the Royal Thai Embass
Study of shuttle imaging microwave system antenna. Volume 1: Conceptual design
A detailed preliminary design and complete performance evaluation are presented of an 11-channel large aperture scanning radiometer antenna for the shuttle imaging microwave system (SIMS) program. Provisions for interfacing the antenna with the space shuttle orbiter are presented and discussed. A program plan for hardware development and a rough order of magnitude (ROM) cost are also included. The conceptual design of the antenna is presented. It consists of a four-meter diameter parabolic torus main reflector, which is a graphite/epoxy shell supported by a graphite/epoxy truss. A rotating feed wheel assembly supports six Gregorian subreflectors covering the upper eight frequency channels from 6.6 GHz through 118.7 GHz, and two three-channel prime forms feed assemblies for 0.6, 1.4, and 2.7 GHz. The feed wheel assembly also holds the radiometers and power supplies, and a drive system using a 400 Hz synchronous motor is described. The RF analysis of the antenna is performed using physical optics procedures for both the dual reflector Gregorian concept and the single reflector prime focus concept. A unique aberration correcting feed for 2.7 GHz is analyzed. A structural analysis is also included. The analyses indicate that the antenna will meet system requirements
EMI measurement and modeling techniques for complex electronic circuits and modules
This dissertation consists of four papers. In the first paper, a combined model for predicting the most critical radiated emissions and total radiated power due to the display signals in a TV by incorporating the main processing board using the Huygens Equivalence theorem and the radiation due to the flex cable based on active probe measurements was developed.
In the second paper, a frequency-tunable resonant magnetic field probe was designed in the frequency range 900-2260 MHz for near-field scanning applications for the radio frequency interference studies by using a varactor diode providing the required capacitance and the parasitic inductance of a magnetic field loop (i.e., a parallel LC circuit). Measurement results showed good agreement with the simulated results.
In the third paper, a wideband microwave method was developed as a means for rapid detection of slight dissimilarities (including counterfeit) and aging effects in integrated circuits (ICs) based on measuring the complex reflection coefficient of an IC when illuminated with an open-ended rectangular waveguide probe, at K-band (18-26.5 GHz) and Ka-band (26.5-40 GHz) microwave frequencies.
In the fourth paper, a method to predict radiated emissions from DC-DC converters with cables attached on the input side to a LISN and on the output side to a DC brushless motor as load based on linear terminal equivalent circuit modeling was demonstrated. The linear terminal equivalent model was extracted using measured input and output side common mode currents for various characterization impedances connected at the input and output terminals of the converter --Abstract, page iv
Prospect of using machine learning-based microwave nondestructive testing technique for corrosion under insulation: A review
Corrosion under insulations is described as localized corrosion that forms because of moisture penetration through the insulation materials or due to contaminants’ presence within the insulation material. The traditional non-destructive inspection techniques operating at a low frequency require removing insulation material to enable inspection, due to poor signal penetration. Several high-frequency inspection
techniques such as the microwave technique have shown successful inspection in detecting the defect under insulations, without removing the insulations. However, the microwave technique faces several challenges such as poor spatial imaging, large errors in terms of defect size and depth owing to stand-off distance variations, optimal frequency point selection, and the presence of the outlier in microwave measurement data. The microwave technique in conjunction with machine learning approaches has tremendous potential and viability for assessing corrosion under insulation. This paper provides an in-depth review of non-destructive techniques for assessing corrosion under insulation, as well as the possibility of using machine learning approaches in microwave techniques in comparison to other conventional techniques
Aeronautical engineerng: A special bibliography with indexes, supplement 36
This special bibliography lists 628 reports, articles, and other documents introduced into the NASA scientific and technical information system in September 1973
Aeronautical engineering: A special bibliography with indexes, supplement 38, December 1973
This special bibliography lists 473 reports, articles, and other documents introduced into the NASA scientific and technical information system in November 1973
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