Date of Award
Master of Science
Department of Engineering Physics
Timothy W. Zens, PhD.
Polyurethane-based aircraft coating degradation was examined using Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs). Two sample sets were aged in an autoclave; each containing four samples. Sample set A contained two as-cured samples and two samples treated to a level of visual degradation. Sample set B contained one sample left as-cured and three samples of differing degradation. DRIFTs spectra were collected on sample set B and singular value decomposition (SVD) was used to reveal trends between the degradation levels. Linear discriminant analysis (LDA) was then applied to the SVD coefficients to determine the most accurate spectral band for classification of unknown degradation. The 1220-850 cm-1 band proved to be the most accurate at discerning between degradation levels with 98.3% accuracy. The approach was then applied to sample set A using one each of the as-cured and degraded samples as unknown degradation levels. The prediction accuracy of LDA was 100% for the as-cured sample, but only 28% for the visibly degraded sample in the fingerprint region. When the misclassification cost was adjusted, the accuracy improved to 78%. It is recommended that this work continue towards generating a field NDI technique.
DTIC Accession Number
Korth, Hans G., "Investigation of the Potential for FTIR as a Nondestructive Inspection Technique for Aircraft Coating Degradation" (2014). Theses and Dissertations. 652.