This paper presents the development of a new non-contact acousto-thermal signature (NCATS) nondestructive evaluation technique. The physical basis of the method is the measurement of the efficiency of the material to convert acoustic energy into heat, and a theoretical model has been used to evaluate this. The increase in temperature due to conversion of acoustic energy injected into the material without direct contact was found to depend on the thermal and elastic properties of the material. In addition, it depends on the experimental parameters of the acoustic source power, the distance between sample and acoustic source, and the period of acoustic excitation. Systematic experimental approaches to optimize each of the experimental variables to maximize the observed temperature changes are described. The potential of the NCATS technique to detect microstructural-level changes in materials is demonstrated by evaluating accumulated damage due to plasticity in Ti-6Al-4V and low level thermal damage in polymer matrix composites. The ability of the technique for macroscopic applications in nondestructive evaluation is demonstrated by imaging a crack in an aluminum test sample.

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In an effort to meet the needs for high frequency eddy current measurements and be able to distinguish small conductivity variations in different materials, a new eddy current module capable of measuring magnitude, phase, and frequency shift was developed and integrated into a general-purpose scanning system. Comparisons of three different parameter images are presented. The potential application of the multi-frequency, multi-parameter eddy current measurement technique for materials characterization to discriminate small conductivity changes is discussed.

Conductivity profile determination by eddy current for shot-peened superalloy surfaces toward residual stress assessment ABSTRACT. The shot peening intensity of nickel base materials has been examined with an innovative eddy current measurement. The goal is to provide a nondestructive tool to quantitatively evaluate the surface conditions after shot peening. Traditionally, the residual stress caused by the shot peening process can be examined by X-ray diffraction. Recent eddy current works have shown promising results in evaluating the small conductivity variation due to the residual stress. This study explores the feasibility of utilizing the cable which connects to a network analyzer and a conventional eddy current probe to monitor the surface conditions due to the shot peening.