Thermal wave imaging for defect determination during automated fibre placement

Due to recent advances in automated fibre placement (AFP) methods there is a demand for non-destructive evaluation of fibres during structural fabrication. A thermal wave imaging technique is proposed for the evaluation of defects in the AFP process, such as misaligned fibres, debonding between layers and broken fibres. The method focuses on the evaluation of thermal images taken with infrared cameras during the AFP fibre placement procedure. Thermal wave imaging determines defects/damages by assessing the uniformity of heat dissipating through materials. This work looks at the potential of such a system to accurately map the AFP process one layer at a time and build a threedimensional defect/damage analysis of the final structure, which would provide potential for automated algorithms to locate areas of misaligned fibres, layer debonding or fibre breaks. Defects were evaluated by capturing thermal images in real-time after fibre placement, this was done by evaluating a simulated AFP process, by adding additional layers to a test sample. By parametrically assessing any changes in results between successively captured areas and layers it was possible to identify defects. An X-Y gantry system was used to provide evidence for the concept in terms of real-time adaptability within the production process of structures, yielding layer by layer information of the built structure, while also providing information about part to part repeatability of the process.