Non-destructive thermography-based system for damage localisation and characterisation during induction welding of thermoplastic composites

In the last decades, advanced thermoplastics matrix composites (TPCs) were recognised as a valid alternative to thermosetting matrices for many advanced applications. One of the advantages in the use of TPCs is the capability to perform fusion bonding which avoids the use of external joints. Induction welding of carbon fiber reinforced TPCs has gained large interest thanks to the minimum surface preparation required, high efficiency and capability to localise heat at the welding surface. This study relies on a thermal wave technique for the in-situ and real-time evaluation of defects during electromagnetic induction welding of TPCs. The technique is based on a methodology which analyses thermal images acquired in real-time during the welding process to reveal discontinuities from variations in heat distribution. Furthermore, the proposed apparatus is used to conduct post-welding inspections on the damaged area for more detailed defects characterisation. An induction welding device is used to perform the bonding process and different kinds of defects were tested and evaluated. Real-time thermal images of the welding process of TCP samples were obtained by using Infrared (IR) cameras. The recorded data were elaborated and used to locate and evaluate the different kinds of damaged samples. A post-welding analysis of a detected damaged region was performed using heating parameters optimised for the thermography scan. Results show the reliability of the method in detecting and characterising the presence of defects during the welding process using the available heating source without altering the process parameters.