b'This research developed an integrated procedure to characterize critical cladding features of ATF using guided ultrasonic waves and machine learning.thickness and uniformity of a coatingnonuniform, deep learning, specifi-in a layered system. A finite elementcally a convolutional neural network analysis model is first used to compu- architecture, is used for classification. tationally model transient, guidedThe network is evaluated, tested, Lamb waves propagating in coatedand recommendations on its use are specimens with different coatinggiven. For Objective 2, dispersion thicknesses. These time-domaincurves of guided waves in a coated signals are then processed withplate can be measured by conducting a two-dimensional Fourier trans- guided wave tests. Since these disper-form to obtain the correspondingsion curves are influenced by the frequencywave number relation,quality of interfacial bond between which are the dispersion maps of thethe coating and the substrate, coated specimen. Dispersion mapsanalysis of the dispersion curves may are characteristic and depend on bothreveal the bond quality.the coating thickness and uniformity,However, solving this inverse plus its elastic properties (which areproblem is extremely difficult. taken to be constant). Computation- In this paper, we will develop an ally simulated dispersion maps forinverse method based on the use a variety of coating properties areof deep-learning neural networks. obtained and then further processedBy using a set of experimentally to extract a feature representationmeasured dispersion curves, this for each dispersion curve. Thoseinverse method will yield the quality extracted features are fed intoof the interfacial bond. We assume machine learning classifiers whichthat the coating-substrate interface allow a thickness classification.is modeled as a linear spring layer This machine learning procedure isof zero thickness. The mechanical shown to be effective in classifyingbehavior of the spring layer is the thickness of a uniform coating.characterized by the spring compli-However, if the coating thickness isance. Both tangential and normal 2023|AFC ACCOMPLISHMENTS 157'