Mold filling process and simulation of sandwich composites with damping layer

Introducing viscoelastic damping layer into composites is an effective method to improve the vibration characteristics of composite structures. Because viscoelastic damping layer is generally hydrophobic material, which hinders resin flow and easily leads to defects. It is very important to analyze the complex flow behavior of resin in sandwich materials. The resin filling behavior in the vacuum assisted resin transfer molding (VARTM) process of perforated silicone rubber sandwich composite was studied.

Firstly, the equivalent permeability of fiber reinforced materials and its combination with the flow medium were tested under constant pressure injected conditions. Secondly, based on the simulation software RTM-Worx, the control volume/finite element method (CV/FEM) was used to track the resin flow front. A filling model of sandwich composites with damping layer was established to simulate VARTM process. By comparing the experimental and simulated resin flow state diagrams and the filling area with times, the effectiveness of the simulation model was verified. Furthermore, the effects of parameters such as the perforation spacing, row spacing, diameter and “edge effect” of the damping layer on the filling time and flow state of the resin were investigated.

The resin filling experiment showed that the flow behavior of the resin in the filling process of the damping layer sandwich composites was as follows: the resin expanded linearly along the plane direction and quickly filled the entire diversion network. At the same time, the resin in the plane of the diversion network penetrated and infiltrated the top laminate along the thickness direction. Then the resin penetrated through the perforations in the damping layer, and then infiltrated and diffused around the perforations as the center. The flow front of the lower plate presented a certain serration shape. The resin flow state and the filling area at different times were compared between experimental and simulated filling. The form and filling rate of resin filling flow were basically the same. The resin flow front of the top laminate expanded linearly forward, and the resin flow front in the bottom laminate was serrated. The simulation of the top and bottom laminates was consistent with the experimental filling rate change trend, which verified the effectiveness of the model. The resin filling process of preforms with different damping layer perforation parameters was simulated, and the influences of perforation spacing, row spacing, diameter and “edge effect” on resin filling of preforms were obtained. The simulation results showed that with the increase of perforation column spacing, the serrated shape of the resin flow front of the laminate becomes deeper and the resin flow synchronization becomes worse. With the increase of perforation row spacing, the resin flow front of the two rows of holes in the front and back of the laminated plate was easy to form interference, resulting in envelope area, thus accumulating bubbles and manufacturing defects. The perforation diameter mainly affected the filling rate. When the diameter was less than 1mm, the filling time increased sharply. The side flow edge effect leaded to poor resin flow front. Some resin overflowed through the exhaust port in advance, so the envelope phenomenon was easy to occur near the exhaust port of the lower composite plate, which increased the filling time.Conclusions: (1) The flow behavior of resin in the filling process of sandwich composites with damping layer can be divided into three stages: The resin is linearly extended to fill the diversion network and the top laminate. Resin fills and penetrates damping layer perforations. Resin diffuses around the center of the perforations in the laminate. (2) The simulation model considers the equivalent permeability of reinforced fiber and diversion net as well as the edge effect of cavity boundary layer. The simulation results are in good agreement with the experimental results, which verifies the effectiveness of the simulation model. (3) Different damping layer perforation parameters have different effects on the filling process : ① The perforation column spacing affects the serrated depth of the laminate flow, and the increase of the spacing deteriorates the resin flow synchronization ; ② Increasing of perforation row spacing leads to interference due to the resin flow front of the adjacent rows holes of the laminate , resulting in envelope area and manufacturing defects ; ③ Perforation diameter mainly affects the filling rate. When the diameter is less than 1mm, a significant increase in the filling time because the resin hardly pass through the hole into the lower laminates; ④ Side flow edge effect leads to poor resin flow front and increase filling time, the lower laminates near the exhaust port position prone to envelope phenomenon.