Ultrasonic Imaging for Internal Defects of Aerospace Irregular Surfaces Structures via CO-SAFT

A reliable non-destructive testing technique for complex surface structures of aerospace vehicles is able to effectively detect and quantify defects in safety-critical surface structures. Traditional Ultrasonic Testing(UL) methods rely on known surface contours, but this method has low surface localization accuracy and poor detection results. This paper presents a curvature-optimized synthetic aperture focusing technique (CO-SAFT) for high-resolution ultrasonic imaging of sub-millimeter internal defects in aerospace curved structures with unknown surface profiles. The phased array transducer acquires full matrix capture (FMC) data by B-scan immersion testing. Artifact suppression is achieved through threshold-based filtering and data fusion, followed by reconstruction of the surface morphology using cubic Hermite interpolation. The robotic arm adjusts the orientation of the single-element probe to the reconstructed surface to ensure normal incidence at each scanning position. Experiments performed on a multi-curvature aluminum specimen with 1 mm artificial defects show a positioning error of 0.5 mm.