CORRECT SIZING OF REFLECTORS IN ULTRASONIC INSPECTION OF THE FORGING TITANIUM ALLOY

Abstract

Commercial Ti-6Al-4V forgings are widely used in the rotating components of aircraft engines. The failure of such parts can be quite catastrophic because of the large amount of kinetic energy. To ensure the safety and longer lifetime of these critical parts working in the hostile environments of high temperature and high stress, the need to detect smaller defects becomes more and more important. Ultrasonic inspection is one of the non-destructive evaluation (NDE) methods widely used by the titanium forging’s manufacturers because of its ability to penetrate the interior of a component. Over the last decade, sizing methods were established like DGS (Distance Gain Size) or DAC (Distance Amplitude Correction) for defects smaller than the beam profile. Those methods utilize the echo amplitude and provide results which are proportional to the defect area. In this article, the correct sizing of small defects below one wavelength is investigated. By properly choosing the simulation method, it is ensured that all physical wave modes are included in the simulation and that the discretization error is negligible. A good correspondence between the simulation and classical defect sizing for defects larger than one wavelength is found. In the region between one quarter of a wavelength and one wavelength resonance effects are found, which results in classical defect sizing methods giving conservative results. In the region below one quarter of a wavelength classical DGS and DAC sizing leads to under-sizing.