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A significant challenge in non-destructive evaluation is the ability to discern signals, originating from a crack and a geometric feature in a part, that are either closely spaced or superimposed in time. An example problem is the ultrasonic inspection of aircraft holes in vertical riser structures with limited accessibility for a transducer from an external wing surface. Characteristics of the path of the ultrasonic signal and the contact condition between the fastener and hole can hinder the use of traditional amplitude dynamics for signal classification and crack detection. A local correlation method was developed to detect the relative shift of signals in time for adjacent transducer locations due to the varying echo dynamics from crack and part geometries. This approach analyses a series of signals from a moving transducer by first accurately aligning the signals to the primary part signal feature and subsequently measuring the shifting of secondary signals of interest within multiple time windows. A methodology is proposed that supplements amplitude dynamic measures with both the change in time and signal variation measures. Feature maps of these dynamic measures are presented to demonstrate the methodology and provide a practical means for classification. Experimental and simulated studies are presented that validate this methodology for several ultrasonic NDE applications. Lastly, an alternative time delay estimation approach is presented for the local correlation method to improve computation time with comparable performance. [ABSTRACT FROM AUTHOR]

Finite element (FE) modeling has been coupled with resonant ultrasound spectroscopy (RUS) for nondestructive evaluation (NDE) of high temperature damage induced by mechanical loading. Forward FE models predict mode-specific changes in resonance frequencies (Δf R ), inform RUS measurements of mode-type, and identify diagnostic resonance modes sensitive to individual or multiple concurrent damage mechanisms. The magnitude of modeled Δf R correlate very well with the magnitude of measured Δf R from RUS, affording quantitative assessments of damage. This approach was employed to study creep damage in a polycrystalline Ni-based superalloy (Mar-M247) at 950°C. After iterative applications of creep strains up to 8.8%, RUS measurements recorded Δf R that correspond to the accumulation of plastic deformation and cracks in the gauge section of a cylindrical dog-bone specimen. Of the first 50 resonance modes that occur, ranging from 3 to 220kHz, modes classified as longitudinal bending were most sensitive to creep damage while transverse bending modes were found to be largely unaffected. Measure to model comparisons of Δf R show that the deformation experienced by the specimen during creep, specifically uniform elongation of the gauge section, is responsible for a majority of the measured Δf R until at least 6.1% creep strain. After 8.8% strain considerable surface cracking along the gauge section of the dog-bone was observed, for which FE models indicate low-frequency longitudinal bending modes are significantly affected. Key differences between historical implementations of RUS for NDE and the FE model-based framework developed herein are discussed, with attention to general implementation of a FE model-based framework for NDE of damage., (Copyright © 2017 Elsevier B.V. All rights reserved.)