Defect Generation Mechanisms in Thick and Variable Thickness Composite Parts - Understanding, Predicting and Mitigation

This project addresses one of the major problems in composite manufacturing: formation of defects and optimisation of processing parameters to mitigate against it. The pre-preg material from which composite components are made can be easily distorted by mechanical action or thermal influence. The final composite undergoes several thermo-mechanical operations where the pre-impregnated system (pre-preg) may be affected: fibre deposition, air removal, consolidation, mould closure, curing under pressure. Each of these operations may result in the deviation of fibres from a determined path. Upon curing the fibrous architecture solidifies and “freezes” all the geometry features which occur at the manufacturing stage. Small (sometimes invisible) fibre path defects have a significantly detrimental effect on the performance of the entire composite structure.
The requirement for sophisticated material control to produce a defect free component is the major impediment to the automation of composite manufacture. The machines handling the pre-preg have to avoid fibre path distortion and yet be able to deform the material in a controllable manner. This requires complete understanding of the defect formation mechanisms, the material properties at all the processing stages, and modelling tools to predict the risk of defect formation for arbitrary tool geometry, materials system, and processing parameters. At present, the processing routes largely rely on intuitive designs. The current project undertakes the analysis of defect occurrence through the entire chain of manufacturing processes with the focus on modern material systems. It aims to create predictive numerical tools which will then in turn be used to develop mitigation strategies for elimination or reduction of defect formation.

EPSRC Centre for Innovative Manufacturing in Composites