An experimental study on filling of gaps and void pockets during vacuum-bag-only consolidation of fiber placed preforms

Gaps and void pockets are inevitably present in tailored thermoplastic composite preforms manufactured via automated fiber placement (AFP). Filling these gaps and voids can be challenging during the consolidation due to the high viscosity of thermoplastic composites, especially in the case of vacuum-bag-only (VBO) consolidation, where the applied pressure is limited. Therefore, the current work investigates whether one bar pressure is sufficient to fill the gaps and voids during VBO consolidation. For this purpose, two experiments are performed. First, a hot plate setup is built and used to capture the real-time gap-filling behavior during the VBO consolidation. Second, VBO consolidation of tailored preforms is performed to study the filling of ply-drop induced void pockets. Here, the tailored preform consists of plies of different orientations dropped at different locations to verify if one bar pressure available during the VBO process is sufficient to fill the void pockets. The results from both experiments answered the main question that one bar pressure is sufficient for filling the gaps and void pockets for the given material systems, and further, it was confirmed that the transverse squeeze flow was dominant in filling gaps. However, in the case of fillings of ply-drop induced void pockets, the orientation of the dropped ply and covering plies majorly dictated the filling behavior.