Strain monitoring by fiber bragg gratings in thick composite cylinders manufacturing

The autoclave process is the main and the most largely diffused technology for high quality polymer composite manufacturing. In autoclave, an heated and highly pressurized air flow allows the curing and the extremely effective compaction of the composite, achieving excellent mechanical properties of the composite. Nevertheless, the high exothermicity of the polymerization and the low thermal conductivity of the thermo-set matrix may increase the risk of the material failure during the manufacturing process. In this paper, the case of a thick composite cylinder that has shown some failures in the real manufacturing process is analysed. Fiber Bragg Gratings (FBG) optical sensors embedded in the composite cylinder during the manufacturing allowed the measurement of process induced strains for the validation of the numerical FEM model of the process, ad-hoc developed. The aim of the model is the evaluation of the risk of failure during cylinder manufacturing. The mechanical model takes into account geometry, stacking sequence, multistep manufacturing process, material thermo viscoelastic anisotropic behaviour and tool-composite interaction as well as heat transfer, cure kinetic and mechanical modelling of gelation during cure.