Phased Array Ultrasonic Sector Scan Imaging of Helicopter Damper Bolts Based on Vector Coherence Factor

Abstract

Non-destructive testing of the cracks on the in-service bolt’s shank with size M18 is a challenging technical problem. Due to the weak echo energy of cracks with large buried depths, the conventional phased array ultrasonic sector scan imaging has a low signal-to-noise ratio, resulting in the effective defect echo submerged in the structural wave of bolts. This work proposes a method of phased array ultrasonic sector scan imaging based on vector coherence factors to detect the microcracks on the surface of the bolt shank. This is achieved by weighting the phased array sector scan imaging with the vector coherence factor to detect the microcracks of the in-service helicopter damper bolt. Experimental work is also carried out to contrast the SNR value of cracks at buried depths of 70 mm and 90 mm with traditional phased array ultrasonic sector scanning images. This demonstrates that the proposed phased array ultrasonic sector scan imaging based on vector coherence factors detected the cracks with a depth of 0.1 mm at the buried depth of 90 mm. The SNR value of the cracks at the buried depth 70 mm in DAS_VCF images is improved by 11.67 dB, compared with the traditional DAS images, in the case of the focus depth at 60 mm.