In-Process Monitoring of Induction Welding of Thermoplastic Composites Based on Fiber Optics

Successful induction welding of thermoplastic composites relies on assuring temperature and applied pressure to be in a certain window for a specific time period. Qualifying an induction welding process therefore requires measurement and control of these parameters.


A novel fiber optic based temperature sensor that can be left in the composite part after manufacturing has been developed and tested. The new sensor allows for quality inspection at the weldline during welding of each part, including the series components and therefore reduces uncertainty in joint strength. This will ease process control and design changes, and will allow for feedback control in the welding process.

Standard fiber optic based sensors do not allow for this. Their diameter is too large and will act as a stress raiser in the weld, causing potential failure under cyclic loading. The proposed concept features a sensor with a coating that dissolves (diffuses) during the welding process, having the coating on the sensor blending into the base polymer. The remaining optical fiber is much smaller in diameter and leaves the strength of the part unchanged. The sensor has been successfully used to visualize the temperature distribution in different work pieces during welding in real time.

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This research was performed by a team of researchers and sponsored by the South Carolina Research Authority (SCRA).

Jaspreet Pandher, Dr. Michel van Tooren
SmartState Center for Multifunctional Materials and Structures, University of South Carolina
Mathew Davis
Luna Innovations Incorporated
Jason Fant
Zeus Industrial Products

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