Browsing by Author "Davis, Geo"

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    Near-surface defect detection in additively manufactured components using laser induced phased arrays with surface acoustic wave crosstalk suppression
    (Elsevier, 2023-11-24) Davis, Geo; Stratoudaki, Theodosia; Lukacs, Peter; Riding, Matthew W.; Al Fuwaires, Ahmed; Kamintzis, Panagiotis; Pieris, Don; Keenan, Alan; Wilcox, Paul; Pierce, Gareth; MacLeod, Charles; Williams, Stewart
    In-process inspection of the additive manufacturing process requires a technique that can provide reliable measurements given the extreme operating environments, the small size of the defects and the cyclic melting and heating of the material, caused by subsequently deposited layers. A remote and couplant-free ultrasonic inspection technique using bulk waves that can image near-surface defects could address these in-process inspection requirements. Laser induced phased arrays (LIPA) generate and detect ultrasound based on laser ultrasonics principles, while the array is synthesised in post-processing. However, when using LIPAs for inspection, the surface acoustic waves (SAWs) interfere with the bulk wave modes giving rise to crosstalk and artefacts, which makes near-surface defect imaging difficult. This work experimentally validates and compares five techniques for SAW suppression: amplitude thresholding, mean waveform subtraction, principal component subtraction, frequency-wavenumber filtering, and phase coherence imaging. SAW suppression is demonstrated in ultrasonic images of transverse waves based on 71-element LIPA data synthesised on a Ti-6Al-4V directed energy deposition-arc (DED-Arc/Ti6Al4V) sample with a ∼1 mm diameter side drilled hole, located at ∼4 mm below the inspected surface. The reported results show that the principal component subtraction approach achieved the highest ‘signal-to-crosstalk ratio’ improvement of 16 dB, while successfully suppressing the SAW.
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    Remote ultrasonic imaging of a wire arc additive manufactured Ti-6AI-4V component using laser induced phased array
    (IEEE, 2021-06-28) Lukacs, Peter; Davis, Geo; Stratoudaki, Theodosia; Williams, Stewart; MacLeod, Charles N.; Gachagan, Anthony
    Additive manufacturing (AM) has been revolutionizing the manufacturing industry due to its ability to significantly reduce waste and produce components with intricate shapes. Laser Ultrasonics (LU) is a non-contact and couplant free method to generate and detect ultrasound. LU can accommodate complex component shapes; thus, it has the potential to provide a reliable in-process inspection method for AM components. In recent years the development of Laser Induced Phased Arrays (LIPAs) helped overcome the inherently low signal amplitudes of LU at the non-destructive, thermoelastic regime. In this paper, the Full Matrix Capture data acquisition method is used and a LIPA of 68 elements is synthesized in post processing. The Total Focusing Method imaging algorithm is applied for ultrasonic imaging. The technique is demonstrated on a highly scattering titanium alloy Wire Arc Additive Manufactured (WAAM) component producing high quality ultrasonic images, accurately imaging defects at depths up to 10mm below the inspection surface
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    Remote Ultrasonic Imaging of a Wire Arc Additive Manufactured Ti-6Al-4V Component using Laser Induced Phased Array
    (Cranfield University, 2021-08-18 14:42) Lukacs, Peter; Williams, Stewart; Davis, Geo; MacLeod, Charles; Stratoudaki, Theodosia; Gachagan, Anthony
    Supporting dataset for the publication: "Remote Ultrasonic Imaging of a Wire Arc Additive Manufactured Ti-6Al-4V Component using Laser Induced Phased Array".The file contains all the signals used to produce the images in the paper, using information mentioned in the paper, e.g. pitch and filter centre frequency.