Ultrasonic crack monitoring in extreme and inaccessible environments F. B. Cegla, J.Davies, P. Cawley Non-Destructive Testing Group, Department of Mechanical Engineering Imperial College London, SW7 2AZ,United Kingdom

Waveguide transduction Is crack monitoring possible using an array of waveguides that isolates the sensitive transducer element from the harsh environment? specimen Notch or crack Array of waveguides to isolate transducer from specimen Hot Cold

Indirect Imaging (multi skip) No need for scanning Array imaging using SH waves

10mm 20mm 30 Point sources x1mm spacing y x ROI (x = -15 to +15mm) (y = 0 to -35mm) FE model FE simulations

FE simulation results for a 20mm thick plate

MUX toneburst generator Receiver amplifier ADC PC control specimen Notch or crack High temp. array Tx Rx Experimental setup

5mm 30mm 19 waveguides 2mm spacing z x ROI: x = 0 to +60mm y = 0 to -30mm notch specimen IMAGE Experimental results for 30mm thick plate

5mm deep notch10mm deep notch15mm deep notch Depth in image: 7.2mm Depth in image: 10.6mmDepth in image: 14mm 10.6mm 30 mm thick steel specimens with EDM notches More experimental results with notches

60mm Fatigue Crack ~ 15mm deepFatigue Crack ~ 20mm deep 12.8 mm 18 mm 60 mm thick steel specimens. Exact crack depths unknown Experimental results with fatigue crack specimens

5mm deep notch Velocity used = 3100 m/s (velocity is temperature dependent) 6.6 mm 30mm 60mm Experimental with specimen at 290  C

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