Annular Phased Array Probe and Dynamical Depth Focussing for Replacement of Multizone Testing

Köhler, Bernd; Fraunhofer IKTS; Germany

Barth, M.; Fraunhofer Institute for Ceramic Technologies and Systems IKTS; Germany
Beggerow, T.; Büro für Technische Diagnostik; Germany
Bron, M.; ScanMaster Systems Ltd.; Israel
Köhler, B.; Fraunhofer Institute for Ceramic Technologies and Systems IKTS; Germany
Rjelka, M.; Fraunhofer Institute for Ceramic Technologies and Systems IKTS; Germany
Spruch, W.; Büro für Technische Diagnostik; Germany

ID: ECNDT-0363-2018
Session: Ultrasonic Inspection, Transducers
Room: G2
Date: 2018-06-12
Time: 15:40 - 16:00

Ultrasonic testing of airplane jet engine disks pose high challenges in finding very small flaws in highly scattering materials as titanium alloys and nickel based super alloys. At the moment this testing is performed as multizone testing meaning that a series of scans is performed with focusing conventional probes at various depths of the disk. We propose to apply annular phased arrays (APA) together with dynamic depth focusing DDF [1]. This approach is aimed to detect defects equivalent to FBH 0.2 mm in contrast to the currently achievable FBH 0.4 mm. With the help of sound field simulations it is shown, that a non-planar APA of special curvature is more suited for the approach as APA transducers with plane faces, which are commercially available. The sound field of the produced transducer agrees with the predictions of our simulations. The transducer can be successfully applied in the variants (i) standard phased array operation, (ii) transmission as axicon [2,3] and reception with fixed focus and (iii) reception with DDF (Figure 1). With DDF all test flaws over the whole sample depth is sharply mapped with only one shot per position.
In a titanium alloy turbine disc a 0.2 mm FBH could be detected.

Figure 1. Side drilled holes imaged with the APA probe. The steel test specimen has a thickness of 125 mm and hole diameters of 2,5 mm. Left: Standard focussing to the half of the sample thickness, Middle: axicon like transmission and standard receiving (focussing to the sample centre) ; Right: axicon like transmission and DDF receiving;

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