Optimisation of double diaphragm forming process through local adjustment of in-plane constraint

In double diaphragm preforming (DDF) of non-crimp reinforcement fabrics, rigid blocks, called “risers”, were introduced for adjustment of local in-plane constraints to improve fabric forming. Optimisation of the riser arrangement to minimise defect formation was implemented through riser position optimisation and riser height optimisation. A simplified finite element (FE) model was developed to simulate the DDF process for the optimisation employing a genetic algorithm (GA). The fabric behaviour was described by a non-orthogonal constitutive relation. The contribution of the diaphragms was embedded within the fabric model in regions where the diaphragm was in direct contact with the preform; in all other areas, a series of 1D spring elements were used to represent the stiffness of the diaphragm, which were connected to the edge of the fabric plies and to a rigid outer frame. Then, the optimised riser positions were adopted, and simulations were run using a detailed FE model to determine the optimal riser height. Simulations indicate that there is limited space to improve the formability by the introduction of risers in DDF. The development of this optimisation approach facilitates the discovery of the maximum capability of placing risers for defect reduction in this process.