Enhanced fabrication process for in situ triboluminescent optical fiber sensor for multifunctional composites

The in situ triboluminescent optical fiber (ITOF) sensor is a proprietary sensor developed by High-Performance Materials Institute researchers. The ITOF sensor consists of polymer optical fiber and manganese-doped zinc sulfide (ZnS:Mn) which has the highest triboluminescent (TL) emission capability among all inorganic crystals. An automated fabrication machine was designed to fabricate consistent ITOF sensor, i.e. uniform TL coating on optical fiber, by a continuous dip coating process. The consistency of the coating thickness depends on the stress distribution on the ITOF sensor, and the vertical alignment of the fiber during the coating process. Several batches of ITOF sensors with different thickness were fabricated by the automated coating machine. The average diameter of the ITOF sensor is approximately 1.51 mm and 1.45 mm for 30 wt% and 50 wt% crystals, respectively, at coating speed of 1.618 mm s−1. The ITOF sensors were embedded into the glass fiber composites and tested under flexural loading to detect composite failure. Results showed that ITOF sensors can detect shear failure of the flexural beams, and the TL signals were impeccably aligned with the acoustic signals. The compact ITOF sensor fabrication machine can consistently, continuously produce ITOF sensors with almost zero waste.