Experimental and numerical investigations on formability of out-of-autoclave thermoset prepreg using a double diaphragm process

The formability of textile out-of-autoclave thermoset prepreg using double diaphragm forming has been investigated to produce a component for aerospace applications. A one-step procedure has been used for both the forming and curing processes using the same experimental setup. A finite element model has been developed to simulate the double diaphragm forming process, with consideration for the diaphragm material properties at forming conditions. To identify potential causes for wrinkle development, important considerations, such as local fiber compressive stresses, shear angle distributions, and stacking lay-up sequences, have been analyzed. Furthermore, different forming simulation scenarios were applied to reduce the wrinkle defects. Results indicate that a change in lay-up sequences significantly affects the formability; thus, wrinkle formations cannot be avoided at challenging locations for some lay-up arrangements. The forming simulations are in agreement with the experimental results in terms of prediction of large wrinkles and intra-ply shear. Meanwhile, high local compressive stress regions provide a good indication for where the critical areas appear, which can be considered when the small wrinkles cannot be predicted with the element size used.