Distributed internal strain measurement during composite manufacturing using optical fibre sensors

Abstract

Due to the advantageous mechanical properties and lowering production costs, carbon fibre composites have increasingly been used for several applications among different industrial sectors in the last decades. However, after manufacturing, a composite part is inevitably expected to store within residual stresses that might affect the shape and mechanical response of the component itself. Understanding how these internal stresses emerge can suggest improved part design and manufacturing conditions to help lower and/or control the residual stress after the composite conception. In the present work, a fully distributed optical fibre sensor (DOFS) with millimetre spatial resolution was embedded in carbon fibre reinforced epoxy panels, measuring the development and build-up of residual strain by monitoring in-situ and in real-time the manufacturing process, from the resin infusion to the curing cycle, recording the changes experienced internally. A commercial optical distributed sensor interrogator detects and measures changes in strain and temperature along the optical fibre length with high precision and accuracy, making it possible to obtain a full strain/temperature profile. Data acquired from the embedded sensor led to track and characterise the strain profile at every stage of the manufacturing process and the epoxy resin phases along with the temperature variations while curing, helping detect and identify a failure during panel manufacture. Moreover, the results obtained show a quite close relation between the infusion stage and the residual strain measured after the curing process. The DOFS resulted to be an accurate and non-detrimental tool for real-time monitoring of composite manufacture, obtaining similar results shown in previous works which employed single-point fibre Bragg grating (FBG) sensors.

Date of Award	31 Dec 2016
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Matthieu Gresil (Supervisor) & Constantinos Soutis (Supervisor)