In-situ process monitoring in automated fibre placement-based manufacturing of advanced composites

Abstract

The automated fibre placement (AFP) offers high throughput and efficient manufacturing methods for making multi- stiffened laminated composites. This revolutionary technique has opened up a wide range of applications and new markets for fibre-reinforced composite materials in many industrial applications like aerospace. However, processing conditions, machine tolerances and steering of material can induce random defects within the laminate, which may compromise the structural integrity. The presence of such defects may result in catastrophic failure of AFP manufactured laminates, hence identifying them at the earlier stages of manufacturing is critical to ensure the quality of final product. The objective of this thesis is to establish a reliable inspection technique for AFP to ensure the structural integrity. An on-line monitoring technique need to be developed for in-situ health monitoring of AFP composites that has been a major concern of composite manufacturers. In this thesis, a novel method using optical fibre Bragg grating (FBG) sensor is implemented towards the in-situ process monitoring of AFP. As a preliminary study, Carbon/Glass fibre reinforced polymer composite specimens with embedded sensor were made using conventional manufacturing methods and their performance were studied under different loading conditions. Then, the FBGs were embedded within the AFP manufactured laminates for in-situ layup process monitoring and identifying misalignment defects which were artificially created between the plies. Moreover, a new sensing head was utilised to discriminate the strain and temperature effects. Finally, the computational approach is carried out using finite element analysis to validate the experimental results. Through a series of experimental studies it is shown that, the lay-up process conditions and misalignment defects can be monitored successfully using FBGs via measuring the reflected wavelengths, which are related to consolidation pressure and curing temperatures. It can also be witnessed that the effects of stacking plies, recovering time and residual strain on the measured wavelength can be measured in real time. Finally, it is demonstrated that by utilising a new FBG configuration the strain and temperature during the lay-up process can be measured simultaneously. The measured strain and temperature values were in the acceptable range, establishing the close agreement of experimental and simulation results.