Measuring the Two-Dimensional Temperature Profile of Carbon Fiber Reinforced Polymers During Drilling Using Distributed Fiber Sensing

The spatio-temporal evolution of the temperature induced over carbon fiber reinforced polymer (CFRP) laminates during drilling is monitored in real-time using a distributed optical fiber sensor based on optical frequency-domain reflectometry (OFDR). The proposed distributed measurement technique enables the simultaneous monitoring of thousands independent points on a CFRP plate during machining, being of special interest to measure the internal temperature of a workpiece. Experimental results validate the use of distributed OFDR-based sensing for this novel application, demonstrating a precise reconstruction of the two-dimensional (2D) temperature profile around the drilled hole, with a 2 mm spatial resolution and a sampling rate of 23.8 Hz (corresponding to a measurement interval of 42 ms). The high spatial and temporal resolutions provided by OFDR sensing offer unique features for this application, allowing for an accurate identification of the temporal evolution and spatial distribution of the 2D temperature profile originated during drilling. By embedding the sensing optical fiber in the interface between CFRP laminates and metals, a full map of the internal (interlayer) temperature of the CFRP plate can be obtained, demonstrating a feature that cannot be obtained by any other sensing technology. The proposed method can constitute a relevant tool for the identification of potential high temperatures occurring during machining, which could affect the quality of the borehole, induce material defects and compromise the safety of an entire composite structure in service.