Induction thermography for unidirectional CFRP composites: A novel inspection approach through global current path integration

In the evolving field of non-destructive testing of composite materials, induction thermography offers significant potential. However, its application to Unidirectional Carbon Fiber Reinforced Polymer (UD CFRP) composites remains challenging due to the unavailability of global current paths. This study introduces a novel methodology to inspect UD CFRP composites using Induction Thermography by incorporating an additional conduction current loop between the composite layers. Initial proof-of-concept experiments were conducted on fiber tow and further validated on laminates. The findings substantiate that the integration of a global current path notably facilitates laminate heating, enhancing the induction thermographic inspection capability. An unexpected discovery in our research is the ability of a circular coil to detect fiber breakage in a laminate that is nearly an order of magnitude wider than the coil diameter, thus demonstrating the approach's high sensitivity. The practical applicability of the proposed methodology was demonstrated using an external fixture. Moreover, this work proposes an innovative modification to the manufacturing process of non-crimp textiles by incorporating a conductive thread, envisaged to bolster the induction thermographic inspection efficiency further. Numerical modeling, closely aligning with experimental observations, provides a robust theoretical foundation for our work.