Non-contact detection of the interfacial microdefects in metal/CFRP hybrid composites using air-coupled laser ultrasound

Metal/CFRP (carbon fiber reinforced plastic) hybrid composites are crucial in aerospace applications, demanding non-contact, high-resolution inspection. Traditional non-destructive testing methods face daunting technical challenges due to varying densities and impedance between fiber and metal layers. Here, a hybrid air-coupled laser-ultrasound (ACLU) system was presented for non-contact detection of internal microdefects on the non-homogeneous metal/CFRP interface. The near-surface resolution of the system can reach as high as 80 µm on a long effective working distance of 50 mm. Three types of experiments, specifically ACLU, phased-array, and X-ray inspection, were performed in Al/CFRP composites with the interfacial microdefects located in Al, bonded, and CFRP layers respectively. Comparing with traditional methods, the proposed ACLU system can detect the microdefects of bonding failure, cohesive failure, and delamination at the Al/CFRP interface with higher contrast, resolution, and sensitivity. A significant advantage of the ACLU system is its ability to detect defects on curved surface structure materials, making it highly versatile for various composite configurations. Our eventual goal is to offer an affordable non-contact laser-ultrasound approach for quality and damage inspection of metal/CFRP hybrid composites.