Terahertz NDE application for corrosion detection and evaluation under Shuttle tiles

Abstract

Pulsed Terahertz NDE is being examined as a method to inspect for possible corrosion under Space Shuttle Tiles. Other methods such as ultrasonics, infrared, eddy current and microwave technologies have demonstrable shortcomings for tile NDE. This work applies Terahertz NDE, in the frequency range between 50 GHz and 1 THz, for the inspection of manufactured corrosion samples. The samples consist of induced corrosion spots that range in diameter (2.54 to 15.2 mm) and depth (0.036 to 0.787 mm) in an aluminum substrate material covered with tiles. Results of these measurements are presented for known corrosion flaws both covered and uncovered and for blind tests with unknown corrosion flaws covered with attached tiles. The Terahertz NDE system is shown to detect all artificially manufactured corrosion regions under a Shuttle tile with a depth greater than 0.13 mm.

Gas-phase broadband spectroscopy using active sources: progress, status, and applications [Invited]

“…The transmission of THz light through samples opaque in the infrared and visible is also attractive for sensing of concealed explosives, and THz-TDS has been demonstrated as an effective tool for differentiating explosives based on their characteristic vibrational and phonon absorptions [284]. A related application is the non destructive examination of space shuttle tiles with THz-TDS, particularly in corrosion and defect detection [285]. …”

Terahertz Spectroscopy and Brewster Angle Reflection Imaging of Acoustic Tiles

“…For example, it has proven suitable for imaging defects in foam insulation within the fuel tanks of the NASA space shuttle [5]. THz reflection tomography [6] has been demonstrated using coherently detected THz pulses and has been used for applications ranging from the imaging of delaminations [7] and under paint corrosion [8,9] to art conservation [10]. THz radiation is also extremely sensitive to water which absorbs it strongly in the far infrared.…”

Terahertz reflection time-domain spectroscopy for imaging and identifying concealed interfaces in multilayered systems

“…to absorption spectroscopy for the identification of drugs/explosives [18], to security screening applications [11], and finally to the detection of flaws in materials within insulated systems such as submarine hulls [19] and the NASA space shuttle foam insulation [20]. Imaging with THz can be performed in a transmission or reflection geometry, each of these methods specialized for certain applications based on their respective strengths and weaknesses.…”

“…It is also complicated by the fact that a well-defined reference, required for spectroscopy, is not always possible to collect. THz-TDS reflection imaging is involved in art conservation [7], under paint corrosion detection [26], and concealed interface inspection such as foam insulation defect detection in the NASA space shuttle [20] and void detection in submarine acoustic tiles [19]. Fukunaga and Picollo demonstrate the impact that THz reflection spectroscopy could have on art conservation [7].…”

“…In a similar apparatus, NDE for foam insulation and shuttle tiles on the NASA space shuttle has shown to be suitable with THz frequencies. Anastasi et al compare the THz reflection images of corroded aluminum with the same sample concealed by the shuttle tiles [20]. It is concluded that the newfound ability to detect corrosion in a layered system from access to only one side of the sample is more difficult to detect with shuttle tiles that absorb heavily at THz frequencies.…”