High Quality Ultrasonic Imaging at Low Detection Frequency for Defects in Thick Composites

Abstract

Improving detection accuracy without reducing detection depth has always been a challenge in ultrasound imaging. For multi-layer anisotropic carbon fiber reinforced polymers (CFRPs), the propagation path of ultrasonic waves becomes complex with severe attenuation. To improve the imaging accuracy of defects in CFRPs, a beam multiply and sum method suitable for full matrix data, FM-BMAS, has been proposed. This method introduces the spatial coherence of ultrasonic array signals through cross-multiplication operation. A new harmonic component is generated and high-quality imaging of side-drilled holes (SDHs) is achieved without affecting the detection depth. The FM-BMAS method can detect two SDHs with a diameter of 1 mm at a depth of 8 mm at 2.5 MHz detection frequency. In contrast, these defects cannot be visualized by the classical total focusing method due to ultrasonic attenuation even with 5 MHz detection frequency. Furthermore, FM-BMAS can achieve higher image resolution and superior noise suppression capabilities in CFRPs compared to other methods.