Corner inspection method for L-shaped composite structures using laser ultrasonic rotational scanning technique

Composite primary structures that can sustain high loads are used to reduce the weight of structures in various industries. Composite primary structures that are L-shaped or T-shaped have a right-angled corner, and phased-array ultrasonic inspection or water squirt robotic C-scan is mainly used for the corners. However, using a customized transducer has restrictions depending on the size and shape of the corner. In this paper, we propose a novel approach based on rotational laser ultrasonic inspection for even narrow corner sections regardless of size and angle. In the rotational scanning method, the target structure is rotated for inspection, which is different from conventional scanning methods in which transducers or a scanning head are moved along the inspection area. The rotational scanning method is designed to solve the problem of signal-to-noise ratio deterioration that occurs when the ultrasonic sensing laser scans a curved surface. The corner sections of two L-shaped specimens fabricated by autoclave curing and resin transfer molding were inspected using the rotational scanning method. Using the proposed method, all of the artificial defects inserted into the corner section of the specimens were clearly visualized. Then, the inspection results were compared with water squirt C-scan inspection results. The test results showed that the proposed method is highly reliable and useful for inspecting the corner sections.