Optical fibre sensor with 3D printed package configuration: A potential revolution of structural strain testing

Monitoring of stress/strain is of particular importance to understand better the mechanical parameters which underpin the condition of a wide variety of structures. Although they were initially developed some 30 years ago, optical fibre sensors have not been widely used in this field and the traditional strain gauges still dominate the market. During recent years, optical fibre sensors, especially Fibre Brag Grating (FBG) sensors, have received intensive attention with considerable research and development to allow them to be applied successfully in many engineering fields, including in a number of structural health monitoring systems. However, ensuring the structural integrity of the FBG sensor and providing robust ‘packaging’ for the device remains a key issue, which becomes a major concern when applying these in various structural strain test methods. To protect FBG sensors in use, a number of packaging techniques have been proposed, including metal, fibre reinforcement polymers and different types of epoxy. However, often such packaging is either insufficiently flexible or expensive. The recent development of 3D printing technologies provides a new and rapid solution for the packaging of FBG sensors, which allows the user easily to define the size and property of the sensor package tailoring that to the specific application. In this study, to examine the use of these techniques for structural monitoring, several different printing materials were used with FBG-based sensors and their properties compared, with the optimal sizes for the packages used being identified. Experimental studies were conducted on a steel beam under repeated stepped loading and unloading processes with different sensor packages. To compare the performances of the traditional strain gauge and these FBG-based sensors, both types were attached on the beam to record the strain changes during the tests. The results demonstrate that the 3D printed packaged sensor designs are highly suitable for use in structural strain testing, and that the performance of FBG sensor thus configured is as stable and consistent in performance as is the familiar strain gauge counterpart.