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

The automated fibre placement (AFP) offers high throughput and efficient manufacturing methods for making multi- stiffenedlaminated composites. This revolutionary technique has opened up a wide range of applications and newmarkets for fibre-reinforced composite materials in many industrial applications like aerospace. However, processingconditions, machine tolerances and steering of material can induce random defects within the laminate, which maycompromise the structural integrity. The presence of such defects may result in catastrophic failure of AFPmanufactured laminates, hence identifying them at the earlier stages of manufacturing is critical to ensure the qualityof final product. The objective of this thesis is to establish a reliable inspection technique for AFP to ensure thestructural integrity. An on-line monitoring technique need to be developed for in-situ health monitoring of AFPcomposites 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-situprocess monitoring of AFP. As a preliminary study, Carbon/Glass fibre reinforced polymer composite specimens withembedded sensor were made using conventional manufacturing methods and their performance were studied underdifferent loading conditions. Then, the FBGs were embedded within the AFP manufactured laminates for in-situ layupprocess 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, thecomputational 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 canbe monitored successfully using FBGs via measuring the reflected wavelengths, which are related to consolidationpressure and curing temperatures. It can also be witnessed that the effects of stacking plies, recovering time andresidual strain on the measured wavelength can be measured in real time. Finally, it is demonstrated that by utilising anew FBG configuration the strain and temperature during the lay-up process can be measured simultaneously. Themeasured strain and temperature values were in the acceptable range, establishing the close agreement ofexperimental and simulation results