Predicting Formation of Manufacturing Defects in Contoured Composites

Composite helicopter rotor components are typically thick and often have areas with a tight radius of curvature, which make them especially prone to process-induced defects, including wrinkles and voids at ply interfaces. Such flaws cause high rejection rates in production of flight-critical components and structure. This work seeks to fill the gaps in understanding generation of the noted defects in contoured polymer-matrix composite (PMC) laminates. In particular, understanding and modelling defect formation at the early stages of the manufacturing process might be the missing link to enable the development of practical engineering solutions allowing for better control of the manufacturing process of contoured composite parts. In this work, an approach based on a continuum description of the uncured prepreg material, including the initial bulk or void content, and finite element modelling (FEM) is used to simulate the consolidation process at the early stages of manufacturing of contoured laminates. The simulation predicts instabilities leading to formation of both wrinkles and voids at ply interfaces during laminate debulking or vacuum consolidation. Applicability of the method to consolidation in both closed-cavity and open-face tooling is also demonstrated. FEM results show good correlation with X-ray Computed Tomography data. This work also introduces a new simulation concept based on finite element and discrete modelling of voids at ply interfaces to improve accuracy of predicting their evolution during the debulking operations.