Manufacturing of parts with complex geometries is becoming increasingly popular. The relevant manufacturing processes used to produce such parts include 3D printing, castings, forgings and composites. Parts manufactured using these processes often have complex shapes and features that make the nondestructive testing difficult. Phased array ultrasonic testing of curved parts is typically performed in immersion. However, even in that case, the curvature of the external surface disrupts the image reconstruction, making it harder to detect subsurface flaws. In this context, this paper focuses on the influence of the water path length between the probe and the part as a function of the part’s surface curvature when using the adaptive total focusing method. Simulations of inspection using the CIVA software were conducted for a set of aluminum parts with convex and concave top surfaces. A phased array probe with 64 elements and a centre frequency of 5 MHz was used. Each simulated part contained five side-drilled holes with a diameter of 1 mm. Both sinusoidal concave and convex surfaces were analyzed: varying from a flat surface to a sine amplitude of 25 λ~Aluminum~. In all cases, the wavelength of the sine was fixed to twice the probe aperture.  These sharp curvatures relative to the probe aperture emulate the spectrum of slopes that may be present in the inspection of complex parts. The flat case was used as a benchmark for the following comparison metrics: (1) the signal-to-noise ratio (SNR), (2) the maximum pixel intensity of a reflector and (3) the array performance indicator. Results show that the imaging performance depends on the top surface curvature, the defect position and more importantly on the water path length. The results suggest that the imaging can be greatly improved by adapting the water path length to the curvature. Finally, experiments were carried out to verify the validity of the numerical findings. Five parts were machined with different top surface curvatures. The experimental setup comprised a Verasonics Vantage 64 LE array controller and a 64 element 5 MHz Olympus phased array probe. Full matrix captures were acquired for 10 water path lengths varying from 40 to 130 mm and the adaptive total focusing method images were generated. The experiments and the simulations were found to be in good agreement. As an example, the results show that for a concave sinusoidal top surface with an amplitude of 5 λ~Aluminum~, the pixel intensity at a side-drilled hole can gain up to 19 dB  and the SNR around the defect can be increased by 16 dB when using the optimal water path length.        


Influence of Surface Curvature and Probe Position in Phased Array Ultrasonic Testing

No proceedings papers in 2020. Video only.

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