Resin pressure and resin flow inside tapered laminates during zero-bleeding and bleeding processes

Resin pressure greatly influences resin flow, void defect, and fiber distribution inside the laminates, especially inside the composite with complex geometry. Thus, obtaining a fundamental understanding on the resin pressure inside laminates with complex shapes can provide an important guidance to control these qualities. This article is mainly focused on the resin pressure inside the composite laminates with tapered thickness and its effect on the compaction of fiber bed. The resin pressure variations inside carbon fiber fabric/epoxy resin prepreg stacks during zero-bleeding and bleeding processes were investigated by means of an on-line monitoring method. It is demonstrated that significant differences are found between the two cases. The resin pressure inside tapered stack under zero-bleeding condition evenly distributes throughout the whole cycle and leads to even distribution of fiber content. In the case of bleeding condition, the application of bleeder materials results in through-thickness and in-plane resin pressure gradients, which provide driving forces for resin flow, and it directly results in different level of fiber compaction at different regions. These results provide a basic understanding on the resin pressure characteristic inside tapered laminate during autoclave process.