Characterisation of process-induced variability in wrinkle defects during double diaphragm forming of non-crimp fabric

Experiments and numerical simulations are employed to determine the critical process variables that affect the quality of a two-layer biaxial non-crimp fabric (NCF) preformed using the double diaphragm forming (DDF) process. To prevent wrinkling defects, the process variables must be controlled, including the vacuum pressure, diaphragm tension, and ply-tool alignment. Inter-ply friction plays a critical role in the deformation mechanism, while the frictional interaction between the diaphragm and tool has a limited impact. The study also reveals that geometrical features have an impact on the variability induced by the forming process. Preforms deformed to tools with geometrical features of higher asymmetry or Gaussian curvatures reduce the uncertainty of the forming process by maintaining the same preform quality despite changes in forming variables.