Phased Array Ultrasonic Testing for Stiffeners in Diffusible Welding With Cavity

Diffusion welding parts with cavities and a stiffener width of 3mm will fail due to defects such as small holes and inclusions in the welding area. However, the thickness of the blank containing the cavity is 40 mm, and the width of the stiffeners is only 3 mm, making it hard for sound waves to reach the stiffeners in ultrasonic testing process. Additionally, complex acoustic reflection structural waves at the stiffeners make it hard to effective detect the internal weld defects in the stiffeners . To address the above difficulties, this work uses a flat bottom hole with a diameter of 0.4 mm to simulate porosity defects, and phased array sector scanning imaging technology to detect the flat bottom hole defects at the 3 mm wide reinforcing rib weld seam. According to the phase distribution characteristics of sector scanning, a phase coherence weighting method is proposed to suppress the non-defective structural echo caused by the complex reflection of stiffener. The results show that the defect can be separated from the non-defective structural wave when the main acoustic axis direction of the probe is parallel to the weld seam and the probe deviates directly above the defect, i.e. the defect deviating by 19° from the center of the sector scan image. However, the greater the deviation of the probe from the defect top, the lower the defect amplitude. After phase coherence processing, non-defective echoes are suppressed, and defects can only deviate by 13° from the center of fan scan image. Compared with the original sector scan image, the deflection angle decreases and the imaging quality of defects is improved.