Role of resin percolation in gap filling mechanisms during the thin ply thermosetting automated tape placement process

During the automated tape placement process, gaps between adjacent tapes are created due to the limitation of machine accuracy, especially at higher speeds. These gaps are undesirable as they cause porosity, thickness variation, and fiber waviness, introducing defects in the composite part. Applying pressure and temperature to part can assist in partially or completely filling these gaps. For thermosetting resins, such processing is usually required for the material to reach complete consolidation. Modeling the tape deformation as squeeze flow of fibrous suspension in the liquid matrix is usually deployed to determine gap filling and tape deformation. However, existence of resin rich zones in the micrographs of fabricated parts suggests that there may be a second flow process involved which is the percolation of matrix through the fiber bed into the remaining empty space of the gaps. This paper extends the previous work that modeled the cross-ply deformation and squeeze flow as the primary mechanisms in the gap filling process during consolidation of thermosetting composites. Based on our experimental results, this work adds the percolation flow to the model to predict (1) the spread of fiber/matrix suspension into the gap, (2) the resin percolation out of the fiber bed into the gap and (3) the deformation of the cross (bridging) ply or plies. The governing equations are formulated, and scaling analysis is performed to estimate the effect of tape thickness on percolation flow confirming that this mechanism is more significant when thin tapes are employed. Fixed mesh numerical scheme is used to evaluate the deformation and flow progression of both the resin percolation flow and the squeeze flow of fiber/resin suspension during the consolidation process. A parametric study is conducted to evaluate the effect of model parameters. Finally, the predicted percolated resin flow along with squeeze flow advancement is compared with experimental results.