Complex shape forming of flax woven fabrics: Design of specific blank-holder shapes to prevent defects

This study concentrates on the possibility of forming a complex shape such as a tetrahedron using two untwisted commercial flax based fabric reinforcements using the sheet forming process. As some of the defects such as tow buckles or tow sliding cannot be predicted and therefore anticipated using simulation techniques, an experimental approach has been used to optimise the process parameters during forming. Specially designed blank holders were used to apply local adapted pressures to the fabric to reduce the pressure in excessively strained tows and to increase the strain in others. The defects previously encountered using a non-optimised blank holder set have been suppressed to a large extent suggesting that most of the commercial untwisted flax based fabrics that enable the best composite properties and best fibre volume fractions can be used to generate the most complex shapes.