Feasibility of ultrasonic phased array inspection on as-forged components

Abstract

In the context of ultrasonic inspection of aircraft engine components, this work investigates the feasibility of performing ultrasonic non-destructive testing on as-forged parts. In partnership with Pratt and Whitney Canada (P&WC), a case study on fan disk forgings that require an extremely high inspection standard was proposed. Therefore, the challenging ultrasonic inspection of parts with complex geometries was researched and developed in three complementary works. First, the reliability of the total focusing method (TFM) applied to specimens with concave and convex profiles was studied in terms of the probe standoff. Artifacts with high amplitude and resolution loss occurred at some profile-standoff combinations. So, a probe standoff optimization method (PSOM) was introduced to mitigate such effects. As a result, considerable TFM improvements were demonstrated at the optimal standoff. The TFM image of a convex specimen had its array performance indicator (API) improved and the signal-to-artifact ratio (SAR) gained up to 13 dB. Lastly, the image under a concave surface gained up to 33 dB in signal-to-artifact ratio. The second study aimed at optimizing the imaging of defects below parts with concave surfaces. A beamforming strategy was proposed to mitigate the poor ultrasound penetration problem. In this method, the refraction was compensated by focusing the ultrasonic beam on points on the specimen’s surface. Using fewer transmissions, the beam computation showed a gain of 12 dB per transmission, and the imaging of a 1 mm side drilled hole presented an improvement of approximately 11 dB in signal-to-noise ratio. The third article presents a novel global TFM (gTFM) to scan a complex specimen representing an aerospace disk forging mock-up. This specimen contained 30 side-drilled holes as sensitivity targets and a profile geometry comprised of multiple concave and convex surfaces. This study combined both previous works through a digital twin of the inspection to optimize the scan plan. Moreover, the ultrasonic phased array probe was scanned around the specimen using a robotic arm, and all acquisitions were combined to generate the global TFM images. The comparison of different scan plans showed that the optimal one, with the probe position adapted to the surface profile, resulted in the sharpest image of the SDHs. This represents a 40% increase in the mean contrast-to-noise ratio (CNR), a 70% reduction in position error (only 0.1mm), and a 33% reduction in the array performance indicator (API). The inspection coverage was efficient, with only seven probe positions needed to depict the complete cross-section of the specimen. Finally, the results of the research on P&WC forgings are presented. The Ni-alloy was characterized and assessed using standard and phased array ultrasonic testing. Then a bore inspection using TFM was proposed and validated as an alternative to increase the inspection sensitivity. A flaw caused in manufacturing was evaluated and sized using a CT scan, standard ultrasonic testing, and TFM. The latter presented the best results with a size error below 10%. To complete the study, an experiment for comparison of sensitivity was designed for P&WC.

Date	5 Dec 2022
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Pierre Bélanger (Supervisor)