Abstract
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.
Highlights
R ECENT progresses in material science and manufacturing techniques have led to a significant increase in the use of carbon fiber reinforced polymer (CFRP) composites for the Manuscript received January 9, 2019; revised April 20, 2019 and May 7, 2019; accepted May 9, 2019
Distributed optical fiber sensing technology with high spatial resolution and fast dynamic sampling rate has demonstrated to be an efficient tool for real-time monitoring of the spatio-temporal evolution of the temperature resulting over CFRP laminates during drilling, as well as of the internal temperature of the workpiece
Experimental results validate the use of optical frequency-domain reflectometry (OFDR) sensing for this novel application of distributed optical fiber sensors, pointing out that the 2D temperature distribution originated during drilling 0°/90 °CFRP plates has a circular zone of high temperature, as seen in the way of a thermal image
Summary
R ECENT progresses in material science and manufacturing techniques have led to a significant increase in the use of carbon fiber reinforced polymer (CFRP) composites for the Manuscript received January 9, 2019; revised April 20, 2019 and May 7, 2019; accepted May 9, 2019. Experimental results demonstrate that the fast interrogation rate of the distributed OFDR sensor allows the detection of the uneven spatial profile of the temperature originated around the borehole when drilling unidirectional carbon fiber laminates. This tilted temperature profile evolution with respect to the carbon fiber direction matches very well with theoretical predictions presented in previous publications [30]; it is believed that the results shown in this paper correspond to the first experimental demonstration of such a phenomenon using a distributed temperature measurement technique
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