Evaluation of manufacturing defects in 3D printed carbon fiber reinforced cylindrical composite structure based on laser ultrasonic testing

Additive manufacturing (AM), also known as three-dimensional (3D) printing technology, has the advantages of rapid modeling of complex shapes and flexibility in design. Nowadays, 3D printing of continuous carbon fiber filaments based on material extrusion (ME) is drawing more attention owing to its advantages in shortening the traditional composite manufacturing process. However, in the 3D printing process, inherent defects occur owing to limitations of the ME-based 3D printing process itself. Because manufacturing defects can deteriorate structural performance, methods for visualizing and minimizing defects are required. In this study, defects in 3D printed cylindrical carbon fiber-reinforced plastic (CFRP) specimens were evaluated using laser ultrasonic testing (LUT) based on the rotational scanning method. From the inspection results of two cylindrical specimens, it was verified that the LUT inspection system and the proposed method are suitable for detecting defects that occur inside the specimen. The process parameters affecting the occurrence of defects are identified through visualization and quantization of inspection results. Research on process parameters that minimize defects can be applied to the continuous fiber 3D printing of complex structures beyond cylindrical structures.