Optimisation of optical fibre using micro-braiding for structural health monitoring

Abstract

Structural health monitoring is a fast growing area used to assess the state of various structures such as aircraft, building, bridge, wind turbine, pipe, automobile through appropriate data processing and interpretation. This article presents a novel technique of optimising the conventional optical fibres used for structural health monitoring, in order to improve their mechanical properties, and handling during the manufacturing process by micro-braiding the optical fibres. This study investigates and compares the tensile properties of the both micro-braided optical fibre and conventional optical fibres through uniaxial tensile tests. Experimental results show 85% improvement in strain at failure for the micro-braided optical fibre when compared to the optical fibres. Moreover, interfacial shear strength comparison, of the braiding yarn, between optical fibres and micro-braided optical fibre (carried out through micro-bond test) has also been conducted. In addition, the effect of embedding both micro-braided and conventional optical fibre in composite was also investigated by three-point bend test. Overall, the mechanical performance of the composite was not affected by the presence of micro-braided optical fibre. This article will also discuss the process and the advantage of micro-braided optical fibre for structural health monitoring.

Cure monitoring and structural health monitoring of composites using micro-braided distributed optical fibre

“…The 47% difference in the residual strain of the bare DOF edge and the MBOF edge could be due to the increase in diameter of the MBOF (~470 µm). The larger diameter introduces resin pockets around the MBOF, as detailed in the authors' previous work [29]. Consequently, this results in more significant compressive strains being recorded when the resin undergoes thermal shrinkage during cooling.…”

“…During the lay-up process, a two-metre length, 155 µm diameter, single-mode, polyimide-coated, silica glass optical fibre sensor, with low-bend-loss, was embedded between the fourth and fifth fibre plies. Part of the DOF length was micro-braided, to facilitate the handling and improve its strength [29], before the embedding process, while the remaining length was left bare. For more details on the microbraiding process, the reader is referred to [29].…”

“…Part of the DOF length was micro-braided, to facilitate the handling and improve its strength [29], before the embedding process, while the remaining length was left bare. For more details on the microbraiding process, the reader is referred to [29]. The DOF was carefully inserted and secured beneath fibre floats in the fabric to remove the need for a bonding agent.…”

“…Optical fibre sensors can be used for in situ composite monitoring since embedding them does not interfere significantly with the structure's mechanical properties [29][30][31]. Insensitivity to electromagnetic interference is another advantage of using optical fibres, compared with other techniques such as dielectric analysis [3,4,32].…”

“…Because of their brittleness and ease of breakage, the handling of these optical fibres during composite manufacture can be challenging [46,47]. Micro-braiding was completed to protect the optical fibres and improve their handling and mechanical properties [29].…”