Nondestructive detection of fatigue damage

Abstract

This paper will discuss the various nondestructive techniques which have been used or which are potentially useful for detection of fatigue damage. The ideal nondestructive testing technique would permit very early detection of fatigue damage so that proper assessment of the severity and rate of severity increase of the structural damage leading to failure can be made. Thus, the most sensitive systems would be capable of detecting motion, pileup, and breakaway of dislocations; the next most sensitive systems would be capable of detecting microcracks; the least sensitive systems would only be capable of detecting macrocracks. It is practically expedient to have nondestructive techniques which can successfully detect fatigue damage in each of these regimes since some components can tolerate larger amounts of fatigue damage or larger crack sizes than others without serious concern for the structural integrity of the component. It will be shown that the best nondestructive technique for detecting and sizing of macrocracks is ultrasonics; the best nondestructive techniques for detection of microcrack formation and possible pre‐microcrack fatigue damage are ultrasonic attenuation and acoustic emission; a large number of nondestructive techniques for residual stress (strain) measurements are candidates for extremely early fatigue damage detection, with current interest primarily directed at ultrasonic wave velocity measurements.