Nondestructive monitoring of aircraft composites using terahertz radiation (original) (raw)
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Aeronautics composite material inspection with a terahertz time-domain spectroscopy system
The usability of pulsed broadband terahertz radiation for the inspection of composite materials from the aeronautics industry is investigated, with the goal of developing a mobile time-domain spectroscopy system that operates in reflection geometry. A wide range of samples based on glass and carbon fiber reinforced plastics with various types of defects is examined using an imaging system; the results are evaluated both in time and frequency domain. The conductivity of carbon fibers prevents penetration of the respective samples but also allows analysis of coatings from the reflected THz pulses. Glass fiber composites are, in principle, transparent for THz radiation, but commonly with significant absorption for wavelengths >1 THz. Depending on depth, matrix material, and size, defects like foreign material inserts, delaminations, or moisture contamination can be visu-alized. If a defect is not too deep in the sample, its location can be correctly identified from the delay between partial reflections at the surface and the defect itself. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10 .1117/1.OE.53.3.031208]
Nondestructive evaluation of aircraft composites using reflective terahertz time domain spectroscopy
NDT & E International, 2010
Terahertz time domain spectroscopy in reflection configuration was assessed as a nondestructive evaluation technique for aircraft glass fiber composites. A technique for measuring the material properties of glass fiber composites using reflection geometry was demonstrated in addition to imaging of damaged glass fiber composites. Surface defects such as localized burn damage, puncture holes, and paint/composite removal were detected using amplitude and phase imaging methods. Hidden voids were also detected using the relative amplitude of the first Fabry-Perot reflection. The depths of discontinuities were then measured using a Fourier technique and then subtracting the incident pulse from the reflected pulse. Finally, nondestructive evaluation techniques for transmission and reflection configurations were compared.
Optics Express, 2008
Terahertz time domain spectroscopy (TDS) was assessed as a nondestructive evaluation technique for aircraft composites. Damage to glass fiber was studied including voids, delaminations, mechanical damage, and heat damage. Measurement of the material properties on samples with localized heat damage showed that burning did not change the refractive index or absorption coefficient noticeably; however, material blistering was detected. Voids were located by TDS transmissive imaging using amplitude and phase techniques. The depth of delaminations was measured via the timing of Fabry-Perot reflections after the main pulse. Evidence of bending stress damage and simulated hidden cracks was also detected with terahertz imaging.
Nondestructive evaluation of aircraft composites using terahertz time domain spectroscopy
2008
Terahertz (THz) time domain spectroscopy (TDS) was assessed as a nondestructive evaluation technique for aircraft composites. Material properties of glass fiber composite were measured using both transmission and reflection configuration. The interaction of THz with a glass fiber composite was then analyzed, including the effects of scattering, absorption, and the index of refraction, as well as effective medium approximations. THz TDS, in both transmission and reflection configuration, was used to study composite damage, including voids, delaminations, mechanical damage, and heat damage. Measurement of the material properties on samples with localized heat damage showed that burning did not change the refractive index or absorption coefficient noticeably; however, material blistering was detected. Voids were located by THz TDS transmission and reflection imaging using amplitude and phase techniques. The depth of delaminations was measured via the timing of Fabry-Perot reflections after the main pulse. Evidence of bending stress damage and simulated hidden cracks was also detected with terahertz imaging. v First, I would like to thank my advisor, Lt Col Matt Bohn, for his guidance in this research, offering skillful advice with the laboratory experimental setup and providing expert scientific insight in helping me to resolve research issues. I would also like to thank Dr. Jim Blackshire of AFRL/RXLP for sponsoring this work and for providing us with representative aircraft composite samples which were essential to the research. In addition, I would like to thank Abel Nunez for his help with image processing and to Jeremy Johnson and AFRL/RXLP for the ultrasound and x-ray images. Thanks to Col Brent Richert and my parents for their encouragement to return to school and earn this degree and to my mother for helping to proofread this dissertation. I would like to thank Epiphany Lutheran Church for its spiritual support along the way. I am very grateful for the birth of my two children who have been an inspiration to me and represent promise for the future. Most of all, I would like to thank my wife for her patience and understanding during the difficult days and nights when I was studying, researching, and writing. I also thank her for her strength in enduring an uncomfortable work situation for 4 years.
Teraherz frequencies electromagnetic waves - a new tool for investigating composite defects
2011
In this paper the possibility of using a modern NDT technique THz electromagnetic waves for composite materials defects detection and identification was investigated. Two technological defects were investigated voids and internal delaminating. The composite materials were hand lay up made. Several kinds of reinforcing fibers (glass, basalt, jute) and polyester resin were used. Glass micro spheres and mica plates were placed at different depths in order to simulate technological defects. The specimens were tested using terahertz frequencies electromagnetic waves. The goal was to verify if the NDT method is appropriate to identify technological defects, misuse damage as well as determine parameters such as depth or size.
Inspection of coatings using terahertz time domain spectroscopy system
AIP Conference Proceedings, 2017
There are many methods of examination of coating failures. This paper presents application of a Terahertz Time Domain Spectroscopy for inspection of thin nonconductive coatings. Results of preliminary tests and results of inspection carried for various kinds of coatings were presented. The coatings containing selected kinds of defects were also prepared and evaluated. The presented results show that the terahertz method can be a good alternative in case of coatings testing.
TeraHertz inspections of painted steel samples
2021 IEEE 8th International Workshop on Metrology for AeroSpace (MetroAeroSpace), 2021
Aerospace industry needs accurate coating thickness measurement as well as adhesion testing for preventing the corrosion of wear of metal substrates. Recently, a constant attention is focused towards the potentialities offered by non-invasive sensing techniques and their technological advancements. This communication deals with time of flight THz imaging, enhanced by a noise filtering procedure based on the Singular Value Decomposition of the data matrix. In this work, THz imaging is exploited to analyse painted steel samples in order to detect paint coating layers and provide images of them and of the interface between the coating layer and the steel substrate.
Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications IX, 2016
A fiber-coupled Terahertz time domain spectroscopy (THz-TDS) system based on photoconductive antennas, pumped by a 100-fs fiber laser, has been used to characterize materials in transmission and reflection mode. THz images are acquired by mounting the samples under investigation on an x-y stage, which is stepped through the beam while the transmitted or reflected THz waveform is captured. The samples include a carbon fiber epoxy composite and a sandwich-structured composite panel with an aramid fiber honeycomb core in between two skin layers of fiberglass reinforced plastic. The former has an artificially induced void, and from a comparison of recorded reflected time-domain signals, with and without the void, a simple model for the structure of the composite is proposed that describes the time-domain signals reasonably well.