Double-diaphragm forming of highly aligned short-fibre preforms for complex composite parts

Forming small to medium composite parts with complex geometries presents significant challenges to engineers, primarily due to material-induced, in-process defects such as fibre bridging and wrinkling, leading to poor mould conformity. These issues are characteristic of continuous fibre preforms and the inextensibility of the fibres. HiPerDiF (High Performance Discontinuous Fibre) technology is a novel manufacturing technique to produce high-performance, aligned discontinuous fibre pre-preg materials. This study investigates the forming characteristics of prepreg manufactured using the HiPerDiF method, highlighting its viability for complex part manufacture where mould conformity is critical. Additionally, a previously developed finite element (FE) model, able to predict the behaviour discontinuous fibre preforms during double diaphragm forming (DDF), was used to obtain insights into the experimentally observed material deformation. The results demonstrated the advantage of the enhanced formability of the HiPerDiF preform, owing to its stretchability in the double-diaphragm vacuum forming process. The FE simulations were shown to be a powerful tool to gain understanding of preforms deformation and thickness variation which are otherwise difficult to measure experimentally.