Depthwise cure monitoring of UV-curable polymers by fiber optic array sensors

Ultraviolet (UV) curable resins have many advantages such as an energy saving feature. However, it is not easy to know whether the cure process completes because degree of cure differ in depth during cure process. Distributed cure monitoring is the best method to solve this problem. In the present study, an array-type sensor where optical fibers were embedded has been developed for measuring distribution of cure degree. At first, measuring performance of the sensor was confirmed by measuring refractive index of silicon oil and epoxy resin with applying heat. The experimental results showed that the sensor had good performance for monitoring cure degree of thermosetting resin. Next, we applied the sensor to monitor cure degree during UV cure process. Three sensing positions were 1, 3, 5 mm from the surface irradiated by a UV light. The measured results showed that the cure reaction at deeper position started later. In addition, it appeared that the cure process rates at the three positions were almost same while the respective maximum temperatures caused by reaction heat were different. From these results, it can be said that the proposed sensor is powerful for monitoring distribution of cure degree of UV curable resins