Complex Shape Forming of Flax Fabrics: Analysis of the Solutions to Prevent Defects
The possibility of manufacturing complex shape composite parts with a good production rate is crucial for the automotive industry. The sheet forming of woven reinforcements is particularly interesting as complex shapes with double or triple curvatures with low curvature radiuses can be obtained. To limit the impact of the part on the environment, the use of flax fiber based reinforcements may be considered for structural or semistructural parts. This study examines the possibility to develop composite parts with complex geometries such as a tetrahedron without defect by using flax based fabrics. An experimental approach is used to identify and quantify the defects that may take place during the sheet forming process of woven natural fiber reinforcements. Wrinkling, tow sliding, tow homogeneity defects and tow buckling are discussed. The origins of the defects are discussed, and solutions to prevent their appearance are proposed. Particularly, solutions to avoid tow buckling caused by the bending of tows during forming are developed. Specially designed flax based reinforcement architecture has been developed. However, if this fabric design has been successful for the tetrahedron shape, it may not be sufficient for other types of shapes and that is why the optimization of the process parameters to prevent occurrence of buckles from a wide range of commercial fabrics was also investigated with success.