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Fiber waviness is one of the most significant defects that occurs in composites due to the severe knockdown in mechanical properties that it causes. This paper investigates the mechanisms for the generation of fiber path defects during processing of composites prepreg materials and proposes new predictive numerical models. A key focus of the work was on thick sections, where consolidation of the ply stack leads to out of plane ply movement. This deformation can either directly lead to fiber waviness or can cause excess fiber length in a ply that in turn leads to the formation of wrinkles. The novel predictive model, built on extensive characterization of prepregs in small-scale compaction tests, was implemented in the finite element software ABAQUS as a bespoke user-defined material. A number of industrially relevant case studies were investigated to demonstrate the formation of defects in typical component features. The validated numerical model was used to extend the understanding gained from manufacturing trials to isolate the influence of various material, geometric, and process parameters on defect formation.

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. AbstractThis paper presents a methodology and research study that characterises toughened materials, as is needed for optimisation of composite manufacturing processes. The specific challenge is to cover all of the stages of advanced composite manufacturing: fibre deposition by automatic fibre placement machines, hot or room temperature debulking, and consolidation in an autoclave. In these processes the material experiences a wide range of processing parameters: pressure, load rate, temperatures, and boundary constraints. In these conditions toughened prepregs, exhibit complex rheological behaviour, with diverse flow and deformation mechanisms at various structural scales. Here a series of experimental results are presented in order to describe the temperature, viscosity, flow mechanisms, and scale-effects of simple un-cured prepreg stacks. The driver for this study is to obtain a further understanding of flow mechanisms throughout the consolidation phase of composites manufacture since fibre path defects are most likely to occur during compaction, prior to vitrification.

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