Simultaneous external and internal inspection of a cylindrical CFRP lattice-skin structure based on rotational ultrasonic propagation imaging and laser displacement sensing

Abstract

Composite lattice-skin structures have been widely used in the aerospace industry to reduce structure weight and fabrication cost. The filament winding technique can be used to manufacture them automatically. However, several defects can occur in every manufacturing step, such as outward dimples (in which the skin swells during the curing process) and de-bonding (in which the rib and skin detach). They drastically reduce the buckling strength under compression and should be evaluated before operation. In this study, we simultaneously inspected the outside and inside of a cylindrical composite lattice-skin structure and visualized external and internal defects based on laser displacement sensing and rotational ultrasonic propagation imaging. An external inspection algorithm that used a laser displacement sensor was added to a previously developed internal inspection algorithm. Then, the accuracy of the laser displacement sensor was confirmed by measuring the groove depth of the composite brake disk. Thereafter, external and internal inspection was simultaneously performed on the composite lattice-skin structure. This system can clearly visualize not only external defects (dimples) using laser displacement sensing with 2D median filtering and 2D fast-Fourier transform but also internal defects (de-bonding) using ultrasonic propagation imaging.