Thermal NDI of resistance welded composite structures

This paper presents a thermography-based approach for the non-destructive inspection (NDI) of thermoplastic composite welds. Termed HELTHY (Heat Emitting Layer for THermographY), the technique makes use of the heating element that is used in the welding process as the source of heat for thermographic inspection. Two techniques were utilised in observing surface signal variations: direct temperature measurement and lockin. An infrared camera was used to acquire the surface temperatures and lockin post-processing to obtain phase images of the weld. Both glass and carbon fibre reinforced thermoplastics of various thicknesses were investigated to determine material influences on the technique. Defects of different size were simulated using inserts placed at the weld line before consolidation. The resulting images were then compared to those from ultrasonic inspection. It was found that HELTHY shows great potential for application in-service NDI of resistance welded structures.