Numerical Study on the Formation of Defects During Double Diaphragm Forming Using a Biaxial Non-crimp Fabric

A macroscopic finite element model was employed to investigate the forming-induced macroscale defects during double diaphragm forming (DDF) using a bi-axial non-crimp fabric. The forming related wrinkling behaviour was predicted by the simulation considering the bending stiffness of the fabric. The location of wrinkles was influenced by the in-plane shear deformation and bridging force in the fabric-diaphragm assembly. The severity of wrinkles was influenced by the layup sequence and the frictional resistance at the fabric-fabric and fabric-diaphragm interfaces. The quad-axial layup [+45º/−45º, 0º/90º] was found to produce more wrinkles than the single-orientation layup, indicating that the dissimilar shear deformation between plies at different orientations can contribute to fabric wrinkling. A parametric analysis indicated that reducing the coefficients of friction at fabric-fabric and fabric-diaphragm interfaces can mitigate wrinkles. The deformation of fabric plies can be affected by the in-plane distance between preforms, when forming multiple components in one DDF operation. The component spacing therefore needs to be designed to ensure the quality of each preform is not adversely affected during multi-component forming.