Structural health monitoring of composite laminates in thermoplastic induction welded joints using electromagnetic field technique

Abstract

This research paper explores the assessment of electrical property changes resulting from damage in a Carbon Fiber Reinforced Polymers (CFRP) laminate and its thermoplastic induction-welded joints. Controlled variations in electrical conductivity and dielectric permittivity were achieved by incorporating square Polytetrafluoroethylene (PTFE) adhesive tapes into both CFRP laminates and the bondline interfaces of induction-welded components. Two elementary and effective sensors, capable of measuring magnetic (Purely Magnetic sensor) and electric fields (Hybrid sensor), were employed to detect these property changes induced by a sinusoidal magnetic field generated by a nearby coil. Both sensors exhibited remarkable sensitivity in identifying variations induced by the smallest artificial defects, measuring 2×2 mm in size. Furthermore, the PM sensor displayed a discernible signal trend corresponding to changes in defect size ranging from 4 to 225 mm square, as well as variations in position within the thickness of the CFRP laminate, extending to a depth of 1.7 mm. These findings underscore the potential of electromagnetic-based structural health monitoring (ESHM) techniques for monitoring the condition of a thermoplastic composite structure and its induction-welded joints.