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A finite element (FE) material model has been developed to simulate the double diaphragm forming (DDF) process, to identify potential defects when forming complex 3D preforms from 2D biaxial non-crimp fabric plies. Three different metrics have been introduced to predict and characterise defects, which include local shear angles to determine ply wrinkling induced by over-shear, compressive strains in the primary fibre directions to determine bundle wrinkling, and tensile stresses in the primary fibre directions to determine fabric bridging . The FE simulation is in good agreement with experiments performed on a demonstrator component. Results indicate that fabric bridging occurs in large-curvature regions, which is the dominant defect in DDF. The axial tensile stress in fibres has been used as a measure to identify suitable positions and orientations for darts, to alleviate fabric bridging and improve surface conformity, whilst minimising the effect on the mechanical performance of the component.

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