The Design and Manufacture of Advanced Functional Composite Materials

Abstract

Optical fibre sensors are crucial in Structural Health Monitoring (SHM) applications for quasidistributed and distributed sensing capability. This thesis reports on the progress made in improving the sensing performance of optical fibres (Fibre Bragg grating and distributed optical fibre) through the textile manufacturing process of micro-braiding. A novel microbraiding technique is utilised to optimise the conventional optical fibre to improve their mechanical properties and handling during its installation for the manufacturing process. By comparing the tensile properties of the micro-braided and conventional optical fibres, experimental results show 85% improvement in the strain at failure for the micro-braided optical fibre. Also, the effect of embedding both micro-braided and conventional optical fibre in composite was investigated by a three-point bend test. Overall, the mechanical performance of the composite was not affected by the presence of micro-braided optical fibre. A distributed optical fibre (DOF) sensor was embedded between glass fibre fabric plies during manufacture; part of the DOF length was micro-braided using glass fibres, while the remaining length was left ‘bare’ (as-received condition). In situ and real-time strain measurement during the laminate infusion and curing processes was completed. Cure monitoring of composite materials using different fibre orientations, sensor locations, raw materials, and manufacturing methods has been widely studied. However, no consensus was reached due to differences in raw materials, temperature profile, manufacturing method, fibre orientation, and sensor location. The manufactured composite plate was then subjected to repeated loading during a quasi-static four-point bending test, and the strain development along the length of the DOF was recorded. Comparable results were obtained from the micro-braided and bare sections of the DOF, showing the suitability of micro-braided optical fibres for real-time strain monitoring in composite structures. The micro‐braided DOF facilitates handling for automated manufacturing methods and can be used to follow the full life cycle of a composite from fabrication till end‐of‐life. The use of the micro-braided and conventional optical fibre for strain monitoring during braiding of preforms was also explored. The importance of micro-braiding was displayed on the grating part of the FBG sensor during the interlacement of the braiding yarn. The microbraided and bare optical fibre’s sensitivity to compression between layers, which causes tension in the layer underneath, was displayed.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Prasad Potluri (Supervisor) & Alberto Saiani (Supervisor)