Surface Adaptive Ultrasonic Testing on Defects in CFRP Radii

The wave propagation behavior is complicated in the radii of carbon fiber reinforced plastics(CFRP), and thus the precise nondestructive testing on defects becomes quite difficult. To improve the testing ability with an ultrasonic linear array probe, surface adaptive ultrasonic (SAUL) testing is performed on a T stringer manufactured with T700/epoxy resin by hot compression curing. Three key issues are studied, including the finite element modeling and experimental verification, the water distance selection and defect imaging, and the quantification methods of planar defects and coverage range in radii. It is indicated that a preset delamination can be effectively identified in both simulation and experiment, but is difficult to be quantified. This is mainly attributed to the strong superficial and interfacial reflection echoes from the ribbed plates, which result in significant noise and poor imaging ability. After optimization of the water distance in SAUL testing, the reflection from the ribbed plates disappears to a great extent, and high-quality imaging of the delamination is obtained. In further, the methods for the sizing of a planar defect and coverage range in radii are proposed. A delamination with a 1.5 mm depth and 4.5 mm length in circumference is quantitatively detected. The errors are 6.7% in depth and 4.4% in circumferential length respectively, which could meet the requirements of engineering applications. The results would give support for the precise inspection of CFRP components. © 2022 Editorial Office of Chinese Journal of Mechanical Engineering. All rights reserved.